reorderbuffer.c

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/*-------------------------------------------------------------------------
 *
 * reorderbuffer.c
 *    PostgreSQL logical replay/reorder buffer management
 *
 *
 * Copyright (c) 2012-2024, PostgreSQL Global Development Group
 *
 *
 * IDENTIFICATION
 *    src/backend/replication/logical/reorderbuffer.c
 *
 * NOTES
 *    This module gets handed individual pieces of transactions in the order
 *    they are written to the WAL and is responsible to reassemble them into
 *    toplevel transaction sized pieces. When a transaction is completely
 *    reassembled - signaled by reading the transaction commit record - it
 *    will then call the output plugin (cf. ReorderBufferCommit()) with the
 *    individual changes. The output plugins rely on snapshots built by
 *    snapbuild.c which hands them to us.
 *
 *    Transactions and subtransactions/savepoints in postgres are not
 *    immediately linked to each other from outside the performing
 *    backend. Only at commit/abort (or special xact_assignment records) they
 *    are linked together. Which means that we will have to splice together a
 *    toplevel transaction from its subtransactions. To do that efficiently we
 *    build a binary heap indexed by the smallest current lsn of the individual
 *    subtransactions' changestreams. As the individual streams are inherently
 *    ordered by LSN - since that is where we build them from - the transaction
 *    can easily be reassembled by always using the subtransaction with the
 *    smallest current LSN from the heap.
 *
 *    In order to cope with large transactions - which can be several times as
 *    big as the available memory - this module supports spooling the contents
 *    of large transactions to disk. When the transaction is replayed the
 *    contents of individual (sub-)transactions will be read from disk in
 *    chunks.
 *
 *    This module also has to deal with reassembling toast records from the
 *    individual chunks stored in WAL. When a new (or initial) version of a
 *    tuple is stored in WAL it will always be preceded by the toast chunks
 *    emitted for the columns stored out of line. Within a single toplevel
 *    transaction there will be no other data carrying records between a row's
 *    toast chunks and the row data itself. See ReorderBufferToast* for
 *    details.
 *
 *    ReorderBuffer uses two special memory context types - SlabContext for
 *    allocations of fixed-length structures (changes and transactions), and
 *    GenerationContext for the variable-length transaction data (allocated
 *    and freed in groups with similar lifespans).
 *
 *    To limit the amount of memory used by decoded changes, we track memory
 *    used at the reorder buffer level (i.e. total amount of memory), and for
 *    each transaction. When the total amount of used memory exceeds the
 *    limit, the transaction consuming the most memory is then serialized to
 *    disk.
 *
 *    Only decoded changes are evicted from memory (spilled to disk), not the
 *    transaction records. The number of toplevel transactions is limited,
 *    but a transaction with many subtransactions may still consume significant
 *    amounts of memory. However, the transaction records are fairly small and
 *    are not included in the memory limit.
 *
 *    The current eviction algorithm is very simple - the transaction is
 *    picked merely by size, while it might be useful to also consider age
 *    (LSN) of the changes for example. With the new Generational memory
 *    allocator, evicting the oldest changes would make it more likely the
 *    memory gets actually freed.
 *
 *    We use a max-heap with transaction size as the key to efficiently find
 *    the largest transaction. We update the max-heap whenever the memory
 *    counter is updated; however transactions with size 0 are not stored in
 *    the heap, because they have no changes to evict.
 *
 *    We still rely on max_changes_in_memory when loading serialized changes
 *    back into memory. At that point we can't use the memory limit directly
 *    as we load the subxacts independently. One option to deal with this
 *    would be to count the subxacts, and allow each to allocate 1/N of the
 *    memory limit. That however does not seem very appealing, because with
 *    many subtransactions it may easily cause thrashing (short cycles of
 *    deserializing and applying very few changes). We probably should give
 *    a bit more memory to the oldest subtransactions, because it's likely
 *    they are the source for the next sequence of changes.
 *
 * -------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <unistd.h>
#include <sys/stat.h>
 
#include "access/detoast.h"
#include "access/heapam.h"
#include "access/rewriteheap.h"
#include "access/transam.h"
#include "access/xact.h"
#include "access/xlog_internal.h"
#include "catalog/catalog.h"
#include "common/int.h"
#include "lib/binaryheap.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "replication/logical.h"
#include "replication/reorderbuffer.h"
#include "replication/slot.h"
#include "replication/snapbuild.h"  /* just for SnapBuildSnapDecRefcount */
#include "storage/bufmgr.h"
#include "storage/fd.h"
#include "storage/sinval.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
#include "utils/rel.h"
#include "utils/relfilenumbermap.h"
 
/* entry for a hash table we use to map from xid to our transaction state */
typedef struct ReorderBufferTXNByIdEnt
{
    TransactionId xid;
    ReorderBufferTXN *txn;
} ReorderBufferTXNByIdEnt;
 
/* data structures for (relfilelocator, ctid) => (cmin, cmax) mapping */
typedef struct ReorderBufferTupleCidKey
{
    RelFileLocator rlocator;
    ItemPointerData tid;
} ReorderBufferTupleCidKey;
 
typedef struct ReorderBufferTupleCidEnt
{
    ReorderBufferTupleCidKey key;
    CommandId   cmin;
    CommandId   cmax;
    CommandId   combocid;       /* just for debugging */
} ReorderBufferTupleCidEnt;
 
/* Virtual file descriptor with file offset tracking */
typedef struct TXNEntryFile
{
    File        vfd;            /* -1 when the file is closed */
    off_t       curOffset;      /* offset for next write or read. Reset to 0
                                 * when vfd is opened. */
} TXNEntryFile;
 
/* k-way in-order change iteration support structures */
typedef struct ReorderBufferIterTXNEntry
{
    XLogRecPtr  lsn;
    ReorderBufferChange *change;
    ReorderBufferTXN *txn;
    TXNEntryFile file;
    XLogSegNo   segno;
} ReorderBufferIterTXNEntry;
 
typedef struct ReorderBufferIterTXNState
{
    binaryheap *heap;
    Size        nr_txns;
    dlist_head  old_change;
    ReorderBufferIterTXNEntry entries[FLEXIBLE_ARRAY_MEMBER];
} ReorderBufferIterTXNState;
 
/* toast datastructures */
typedef struct ReorderBufferToastEnt
{
    Oid         chunk_id;       /* toast_table.chunk_id */
    int32       last_chunk_seq; /* toast_table.chunk_seq of the last chunk we
                                 * have seen */
    Size        num_chunks;     /* number of chunks we've already seen */
    Size        size;           /* combined size of chunks seen */
    dlist_head  chunks;         /* linked list of chunks */
    struct varlena *reconstructed;  /* reconstructed varlena now pointed to in
                                     * main tup */
} ReorderBufferToastEnt;
 
/* Disk serialization support datastructures */
typedef struct ReorderBufferDiskChange
{
    Size        size;
    ReorderBufferChange change;
    /* data follows */
} ReorderBufferDiskChange;
 
#define IsSpecInsert(action) \
( \
    ((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT) \
)
#define IsSpecConfirmOrAbort(action) \
( \
    (((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM) || \
    ((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT)) \
)
#define IsInsertOrUpdate(action) \
( \
    (((action) == REORDER_BUFFER_CHANGE_INSERT) || \
    ((action) == REORDER_BUFFER_CHANGE_UPDATE) || \
    ((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT)) \
)
 
/*
 * Maximum number of changes kept in memory, per transaction. After that,
 * changes are spooled to disk.
 *
 * The current value should be sufficient to decode the entire transaction
 * without hitting disk in OLTP workloads, while starting to spool to disk in
 * other workloads reasonably fast.
 *
 * At some point in the future it probably makes sense to have a more elaborate
 * resource management here, but it's not entirely clear what that would look
 * like.
 */
int         logical_decoding_work_mem;
static const Size max_changes_in_memory = 4096; /* XXX for restore only */
 
/* GUC variable */
int         debug_logical_replication_streaming = DEBUG_LOGICAL_REP_STREAMING_BUFFERED;
 
/* ---------------------------------------
 * primary reorderbuffer support routines
 * ---------------------------------------
 */
static ReorderBufferTXN *ReorderBufferGetTXN(ReorderBuffer *rb);
static void ReorderBufferReturnTXN(ReorderBuffer *rb, ReorderBufferTXN *txn);
static ReorderBufferTXN *ReorderBufferTXNByXid(ReorderBuffer *rb,
                                               TransactionId xid, bool create, bool *is_new,
                                               XLogRecPtr lsn, bool create_as_top);
static void ReorderBufferTransferSnapToParent(ReorderBufferTXN *txn,
                                              ReorderBufferTXN *subtxn);
 
static void AssertTXNLsnOrder(ReorderBuffer *rb);
 
/* ---------------------------------------
 * support functions for lsn-order iterating over the ->changes of a
 * transaction and its subtransactions
 *
 * used for iteration over the k-way heap merge of a transaction and its
 * subtransactions
 * ---------------------------------------
 */
static void ReorderBufferIterTXNInit(ReorderBuffer *rb, ReorderBufferTXN *txn,
                                     ReorderBufferIterTXNState *volatile *iter_state);
static ReorderBufferChange *ReorderBufferIterTXNNext(ReorderBuffer *rb, ReorderBufferIterTXNState *state);
static void ReorderBufferIterTXNFinish(ReorderBuffer *rb,
                                       ReorderBufferIterTXNState *state);
static void ReorderBufferExecuteInvalidations(uint32 nmsgs, SharedInvalidationMessage *msgs);
 
/*
 * ---------------------------------------
 * Disk serialization support functions
 * ---------------------------------------
 */
static void ReorderBufferCheckMemoryLimit(ReorderBuffer *rb);
static void ReorderBufferSerializeTXN(ReorderBuffer *rb, ReorderBufferTXN *txn);
static void ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
                                         int fd, ReorderBufferChange *change);
static Size ReorderBufferRestoreChanges(ReorderBuffer *rb, ReorderBufferTXN *txn,
                                        TXNEntryFile *file, XLogSegNo *segno);
static void ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
                                       char *data);
static void ReorderBufferRestoreCleanup(ReorderBuffer *rb, ReorderBufferTXN *txn);
static void ReorderBufferTruncateTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
                                     bool txn_prepared);
static void ReorderBufferCleanupSerializedTXNs(const char *slotname);
static void ReorderBufferSerializedPath(char *path, ReplicationSlot *slot,
                                        TransactionId xid, XLogSegNo segno);
static int  ReorderBufferTXNSizeCompare(const pairingheap_node *a, const pairingheap_node *b, void *arg);
 
static void ReorderBufferFreeSnap(ReorderBuffer *rb, Snapshot snap);
static Snapshot ReorderBufferCopySnap(ReorderBuffer *rb, Snapshot orig_snap,
                                      ReorderBufferTXN *txn, CommandId cid);
 
/*
 * ---------------------------------------
 * Streaming support functions
 * ---------------------------------------
 */
static inline bool ReorderBufferCanStream(ReorderBuffer *rb);
static inline bool ReorderBufferCanStartStreaming(ReorderBuffer *rb);
static void ReorderBufferStreamTXN(ReorderBuffer *rb, ReorderBufferTXN *txn);
static void ReorderBufferStreamCommit(ReorderBuffer *rb, ReorderBufferTXN *txn);
 
/* ---------------------------------------
 * toast reassembly support
 * ---------------------------------------
 */
static void ReorderBufferToastInitHash(ReorderBuffer *rb, ReorderBufferTXN *txn);
static void ReorderBufferToastReset(ReorderBuffer *rb, ReorderBufferTXN *txn);
static void ReorderBufferToastReplace(ReorderBuffer *rb, ReorderBufferTXN *txn,
                                      Relation relation, ReorderBufferChange *change);
static void ReorderBufferToastAppendChunk(ReorderBuffer *rb, ReorderBufferTXN *txn,
                                          Relation relation, ReorderBufferChange *change);
 
/*
 * ---------------------------------------
 * memory accounting
 * ---------------------------------------
 */
static Size ReorderBufferChangeSize(ReorderBufferChange *change);
static void ReorderBufferChangeMemoryUpdate(ReorderBuffer *rb,
                                            ReorderBufferChange *change,
                                            ReorderBufferTXN *txn,
                                            bool addition, Size sz);
 
/*
 * Allocate a new ReorderBuffer and clean out any old serialized state from
 * prior ReorderBuffer instances for the same slot.
 */
ReorderBuffer *
ReorderBufferAllocate(void)
{
    ReorderBuffer *buffer;
    HASHCTL     hash_ctl;
    MemoryContext new_ctx;
 
    Assert(MyReplicationSlot != NULL);
 
    /* allocate memory in own context, to have better accountability */
    new_ctx = AllocSetContextCreate(CurrentMemoryContext,
                                    "ReorderBuffer",
                                    ALLOCSET_DEFAULT_SIZES);
 
    buffer =
        (ReorderBuffer *) MemoryContextAlloc(new_ctx, sizeof(ReorderBuffer));
 
    memset(&hash_ctl, 0, sizeof(hash_ctl));
 
    buffer->context = new_ctx;
 
    buffer->change_context = SlabContextCreate(new_ctx,
                                               "Change",
                                               SLAB_DEFAULT_BLOCK_SIZE,
                                               sizeof(ReorderBufferChange));
 
    buffer->txn_context = SlabContextCreate(new_ctx,
                                            "TXN",
                                            SLAB_DEFAULT_BLOCK_SIZE,
                                            sizeof(ReorderBufferTXN));
 
    /*
     * To minimize memory fragmentation caused by long-running transactions
     * with changes spanning multiple memory blocks, we use a single
     * fixed-size memory block for decoded tuple storage. The performance
     * testing showed that the default memory block size maintains logical
     * decoding performance without causing fragmentation due to concurrent
     * transactions. One might think that we can use the max size as
     * SLAB_LARGE_BLOCK_SIZE but the test also showed it doesn't help resolve
     * the memory fragmentation.
     */
    buffer->tup_context = GenerationContextCreate(new_ctx,
                                                  "Tuples",
                                                  SLAB_DEFAULT_BLOCK_SIZE,
                                                  SLAB_DEFAULT_BLOCK_SIZE,
                                                  SLAB_DEFAULT_BLOCK_SIZE);
 
    hash_ctl.keysize = sizeof(TransactionId);
    hash_ctl.entrysize = sizeof(ReorderBufferTXNByIdEnt);
    hash_ctl.hcxt = buffer->context;
 
    buffer->by_txn = hash_create("ReorderBufferByXid", 1000, &hash_ctl,
                                 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
 
    buffer->by_txn_last_xid = InvalidTransactionId;
    buffer->by_txn_last_txn = NULL;
 
    buffer->outbuf = NULL;
    buffer->outbufsize = 0;
    buffer->size = 0;
 
    /* txn_heap is ordered by transaction size */
    buffer->txn_heap = pairingheap_allocate(ReorderBufferTXNSizeCompare, NULL);
 
    buffer->spillTxns = 0;
    buffer->spillCount = 0;
    buffer->spillBytes = 0;
    buffer->streamTxns = 0;
    buffer->streamCount = 0;
    buffer->streamBytes = 0;
    buffer->totalTxns = 0;
    buffer->totalBytes = 0;
 
    buffer->current_restart_decoding_lsn = InvalidXLogRecPtr;
 
    dlist_init(&buffer->toplevel_by_lsn);
    dlist_init(&buffer->txns_by_base_snapshot_lsn);
    dclist_init(&buffer->catchange_txns);
 
    /*
     * Ensure there's no stale data from prior uses of this slot, in case some
     * prior exit avoided calling ReorderBufferFree. Failure to do this can
     * produce duplicated txns, and it's very cheap if there's nothing there.
     */
    ReorderBufferCleanupSerializedTXNs(NameStr(MyReplicationSlot->data.name));
 
    return buffer;
}
 
/*
 * Free a ReorderBuffer
 */
void
ReorderBufferFree(ReorderBuffer *rb)
{
    MemoryContext context = rb->context;
 
    /*
     * We free separately allocated data by entirely scrapping reorderbuffer's
     * memory context.
     */
    MemoryContextDelete(context);
 
    /* Free disk space used by unconsumed reorder buffers */
    ReorderBufferCleanupSerializedTXNs(NameStr(MyReplicationSlot->data.name));
}
 
/*
 * Get an unused, possibly preallocated, ReorderBufferTXN.
 */
static ReorderBufferTXN *
ReorderBufferGetTXN(ReorderBuffer *rb)
{
    ReorderBufferTXN *txn;
 
    txn = (ReorderBufferTXN *)
        MemoryContextAlloc(rb->txn_context, sizeof(ReorderBufferTXN));
 
    memset(txn, 0, sizeof(ReorderBufferTXN));
 
    dlist_init(&txn->changes);
    dlist_init(&txn->tuplecids);
    dlist_init(&txn->subtxns);
 
    /* InvalidCommandId is not zero, so set it explicitly */
    txn->command_id = InvalidCommandId;
    txn->output_plugin_private = NULL;
 
    return txn;
}
 
/*
 * Free a ReorderBufferTXN.
 */
static void
ReorderBufferReturnTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
{
    /* clean the lookup cache if we were cached (quite likely) */
    if (rb->by_txn_last_xid == txn->xid)
    {
        rb->by_txn_last_xid = InvalidTransactionId;
        rb->by_txn_last_txn = NULL;
    }
 
    /* free data that's contained */
 
    if (txn->gid != NULL)
    {
        pfree(txn->gid);
        txn->gid = NULL;
    }
 
    if (txn->tuplecid_hash != NULL)
    {
        hash_destroy(txn->tuplecid_hash);
        txn->tuplecid_hash = NULL;
    }
 
    if (txn->invalidations)
    {
        pfree(txn->invalidations);
        txn->invalidations = NULL;
    }
 
    /* Reset the toast hash */
    ReorderBufferToastReset(rb, txn);
 
    /* All changes must be deallocated */
    Assert(txn->size == 0);
 
    pfree(txn);
}
 
/*
 * Get a fresh ReorderBufferChange.
 */
ReorderBufferChange *
ReorderBufferGetChange(ReorderBuffer *rb)
{
    ReorderBufferChange *change;
 
    change = (ReorderBufferChange *)
        MemoryContextAlloc(rb->change_context, sizeof(ReorderBufferChange));
 
    memset(change, 0, sizeof(ReorderBufferChange));
    return change;
}
 
/*
 * Free a ReorderBufferChange and update memory accounting, if requested.
 */
void
ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change,
                          bool upd_mem)
{
    /* update memory accounting info */
    if (upd_mem)
        ReorderBufferChangeMemoryUpdate(rb, change, NULL, false,
                                        ReorderBufferChangeSize(change));
 
    /* free contained data */
    switch (change->action)
    {
        case REORDER_BUFFER_CHANGE_INSERT:
        case REORDER_BUFFER_CHANGE_UPDATE:
        case REORDER_BUFFER_CHANGE_DELETE:
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
            if (change->data.tp.newtuple)
            {
                ReorderBufferReturnTupleBuf(change->data.tp.newtuple);
                change->data.tp.newtuple = NULL;
            }
 
            if (change->data.tp.oldtuple)
            {
                ReorderBufferReturnTupleBuf(change->data.tp.oldtuple);
                change->data.tp.oldtuple = NULL;
            }
            break;
        case REORDER_BUFFER_CHANGE_MESSAGE:
            if (change->data.msg.prefix != NULL)
                pfree(change->data.msg.prefix);
            change->data.msg.prefix = NULL;
            if (change->data.msg.message != NULL)
                pfree(change->data.msg.message);
            change->data.msg.message = NULL;
            break;
        case REORDER_BUFFER_CHANGE_INVALIDATION:
            if (change->data.inval.invalidations)
                pfree(change->data.inval.invalidations);
            change->data.inval.invalidations = NULL;
            break;
        case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
            if (change->data.snapshot)
            {
                ReorderBufferFreeSnap(rb, change->data.snapshot);
                change->data.snapshot = NULL;
            }
            break;
            /* no data in addition to the struct itself */
        case REORDER_BUFFER_CHANGE_TRUNCATE:
            if (change->data.truncate.relids != NULL)
            {
                ReorderBufferReturnRelids(rb, change->data.truncate.relids);
                change->data.truncate.relids = NULL;
            }
            break;
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
        case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
        case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
            break;
    }
 
    pfree(change);
}
 
/*
 * Get a fresh HeapTuple fitting a tuple of size tuple_len (excluding header
 * overhead).
 */
HeapTuple
ReorderBufferGetTupleBuf(ReorderBuffer *rb, Size tuple_len)
{
    HeapTuple   tuple;
    Size        alloc_len;
 
    alloc_len = tuple_len + SizeofHeapTupleHeader;
 
    tuple = (HeapTuple) MemoryContextAlloc(rb->tup_context,
                                           HEAPTUPLESIZE + alloc_len);
    tuple->t_data = (HeapTupleHeader) ((char *) tuple + HEAPTUPLESIZE);
 
    return tuple;
}
 
/*
 * Free a HeapTuple returned by ReorderBufferGetTupleBuf().
 */
void
ReorderBufferReturnTupleBuf(HeapTuple tuple)
{
    pfree(tuple);
}
 
/*
 * Get an array for relids of truncated relations.
 *
 * We use the global memory context (for the whole reorder buffer), because
 * none of the existing ones seems like a good match (some are SLAB, so we
 * can't use those, and tup_context is meant for tuple data, not relids). We
 * could add yet another context, but it seems like an overkill - TRUNCATE is
 * not particularly common operation, so it does not seem worth it.
 */
Oid *
ReorderBufferGetRelids(ReorderBuffer *rb, int nrelids)
{
    Oid        *relids;
    Size        alloc_len;
 
    alloc_len = sizeof(Oid) * nrelids;
 
    relids = (Oid *) MemoryContextAlloc(rb->context, alloc_len);
 
    return relids;
}
 
/*
 * Free an array of relids.
 */
void
ReorderBufferReturnRelids(ReorderBuffer *rb, Oid *relids)
{
    pfree(relids);
}
 
/*
 * Return the ReorderBufferTXN from the given buffer, specified by Xid.
 * If create is true, and a transaction doesn't already exist, create it
 * (with the given LSN, and as top transaction if that's specified);
 * when this happens, is_new is set to true.
 */
static ReorderBufferTXN *
ReorderBufferTXNByXid(ReorderBuffer *rb, TransactionId xid, bool create,
                      bool *is_new, XLogRecPtr lsn, bool create_as_top)
{
    ReorderBufferTXN *txn;
    ReorderBufferTXNByIdEnt *ent;
    bool        found;
 
    Assert(TransactionIdIsValid(xid));
 
    /*
     * Check the one-entry lookup cache first
     */
    if (TransactionIdIsValid(rb->by_txn_last_xid) &&
        rb->by_txn_last_xid == xid)
    {
        txn = rb->by_txn_last_txn;
 
        if (txn != NULL)
        {
            /* found it, and it's valid */
            if (is_new)
                *is_new = false;
            return txn;
        }
 
        /*
         * cached as non-existent, and asked not to create? Then nothing else
         * to do.
         */
        if (!create)
            return NULL;
        /* otherwise fall through to create it */
    }
 
    /*
     * If the cache wasn't hit or it yielded a "does-not-exist" and we want to
     * create an entry.
     */
 
    /* search the lookup table */
    ent = (ReorderBufferTXNByIdEnt *)
        hash_search(rb->by_txn,
                    &xid,
                    create ? HASH_ENTER : HASH_FIND,
                    &found);
    if (found)
        txn = ent->txn;
    else if (create)
    {
        /* initialize the new entry, if creation was requested */
        Assert(ent != NULL);
        Assert(lsn != InvalidXLogRecPtr);
 
        ent->txn = ReorderBufferGetTXN(rb);
        ent->txn->xid = xid;
        txn = ent->txn;
        txn->first_lsn = lsn;
        txn->restart_decoding_lsn = rb->current_restart_decoding_lsn;
 
        if (create_as_top)
        {
            dlist_push_tail(&rb->toplevel_by_lsn, &txn->node);
            AssertTXNLsnOrder(rb);
        }
    }
    else
        txn = NULL;             /* not found and not asked to create */
 
    /* update cache */
    rb->by_txn_last_xid = xid;
    rb->by_txn_last_txn = txn;
 
    if (is_new)
        *is_new = !found;
 
    Assert(!create || txn != NULL);
    return txn;
}
 
/*
 * Record the partial change for the streaming of in-progress transactions.  We
 * can stream only complete changes so if we have a partial change like toast
 * table insert or speculative insert then we mark such a 'txn' so that it
 * can't be streamed.  We also ensure that if the changes in such a 'txn' can
 * be streamed and are above logical_decoding_work_mem threshold then we stream
 * them as soon as we have a complete change.
 */
static void
ReorderBufferProcessPartialChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
                                  ReorderBufferChange *change,
                                  bool toast_insert)
{
    ReorderBufferTXN *toptxn;
 
    /*
     * The partial changes need to be processed only while streaming
     * in-progress transactions.
     */
    if (!ReorderBufferCanStream(rb))
        return;
 
    /* Get the top transaction. */
    toptxn = rbtxn_get_toptxn(txn);
 
    /*
     * Indicate a partial change for toast inserts.  The change will be
     * considered as complete once we get the insert or update on the main
     * table and we are sure that the pending toast chunks are not required
     * anymore.
     *
     * If we allow streaming when there are pending toast chunks then such
     * chunks won't be released till the insert (multi_insert) is complete and
     * we expect the txn to have streamed all changes after streaming.  This
     * restriction is mainly to ensure the correctness of streamed
     * transactions and it doesn't seem worth uplifting such a restriction
     * just to allow this case because anyway we will stream the transaction
     * once such an insert is complete.
     */
    if (toast_insert)
        toptxn->txn_flags |= RBTXN_HAS_PARTIAL_CHANGE;
    else if (rbtxn_has_partial_change(toptxn) &&
             IsInsertOrUpdate(change->action) &&
             change->data.tp.clear_toast_afterwards)
        toptxn->txn_flags &= ~RBTXN_HAS_PARTIAL_CHANGE;
 
    /*
     * Indicate a partial change for speculative inserts.  The change will be
     * considered as complete once we get the speculative confirm or abort
     * token.
     */
    if (IsSpecInsert(change->action))
        toptxn->txn_flags |= RBTXN_HAS_PARTIAL_CHANGE;
    else if (rbtxn_has_partial_change(toptxn) &&
             IsSpecConfirmOrAbort(change->action))
        toptxn->txn_flags &= ~RBTXN_HAS_PARTIAL_CHANGE;
 
    /*
     * Stream the transaction if it is serialized before and the changes are
     * now complete in the top-level transaction.
     *
     * The reason for doing the streaming of such a transaction as soon as we
     * get the complete change for it is that previously it would have reached
     * the memory threshold and wouldn't get streamed because of incomplete
     * changes.  Delaying such transactions would increase apply lag for them.
     */
    if (ReorderBufferCanStartStreaming(rb) &&
        !(rbtxn_has_partial_change(toptxn)) &&
        rbtxn_is_serialized(txn) &&
        rbtxn_has_streamable_change(toptxn))
        ReorderBufferStreamTXN(rb, toptxn);
}
 
/*
 * Queue a change into a transaction so it can be replayed upon commit or will be
 * streamed when we reach logical_decoding_work_mem threshold.
 */
void
ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
                         ReorderBufferChange *change, bool toast_insert)
{
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
 
    /*
     * While streaming the previous changes we have detected that the
     * transaction is aborted.  So there is no point in collecting further
     * changes for it.
     */
    if (txn->concurrent_abort)
    {
        /*
         * We don't need to update memory accounting for this change as we
         * have not added it to the queue yet.
         */
        ReorderBufferReturnChange(rb, change, false);
        return;
    }
 
    /*
     * The changes that are sent downstream are considered streamable.  We
     * remember such transactions so that only those will later be considered
     * for streaming.
     */
    if (change->action == REORDER_BUFFER_CHANGE_INSERT ||
        change->action == REORDER_BUFFER_CHANGE_UPDATE ||
        change->action == REORDER_BUFFER_CHANGE_DELETE ||
        change->action == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT ||
        change->action == REORDER_BUFFER_CHANGE_TRUNCATE ||
        change->action == REORDER_BUFFER_CHANGE_MESSAGE)
    {
        ReorderBufferTXN *toptxn = rbtxn_get_toptxn(txn);
 
        toptxn->txn_flags |= RBTXN_HAS_STREAMABLE_CHANGE;
    }
 
    change->lsn = lsn;
    change->txn = txn;
 
    Assert(InvalidXLogRecPtr != lsn);
    dlist_push_tail(&txn->changes, &change->node);
    txn->nentries++;
    txn->nentries_mem++;
 
    /* update memory accounting information */
    ReorderBufferChangeMemoryUpdate(rb, change, NULL, true,
                                    ReorderBufferChangeSize(change));
 
    /* process partial change */
    ReorderBufferProcessPartialChange(rb, txn, change, toast_insert);
 
    /* check the memory limits and evict something if needed */
    ReorderBufferCheckMemoryLimit(rb);
}
 
/*
 * A transactional message is queued to be processed upon commit and a
 * non-transactional message gets processed immediately.
 */
void
ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid,
                          Snapshot snap, XLogRecPtr lsn,
                          bool transactional, const char *prefix,
                          Size message_size, const char *message)
{
    if (transactional)
    {
        MemoryContext oldcontext;
        ReorderBufferChange *change;
 
        Assert(xid != InvalidTransactionId);
 
        /*
         * We don't expect snapshots for transactional changes - we'll use the
         * snapshot derived later during apply (unless the change gets
         * skipped).
         */
        Assert(!snap);
 
        oldcontext = MemoryContextSwitchTo(rb->context);
 
        change = ReorderBufferGetChange(rb);
        change->action = REORDER_BUFFER_CHANGE_MESSAGE;
        change->data.msg.prefix = pstrdup(prefix);
        change->data.msg.message_size = message_size;
        change->data.msg.message = palloc(message_size);
        memcpy(change->data.msg.message, message, message_size);
 
        ReorderBufferQueueChange(rb, xid, lsn, change, false);
 
        MemoryContextSwitchTo(oldcontext);
    }
    else
    {
        ReorderBufferTXN *txn = NULL;
        volatile Snapshot snapshot_now = snap;
 
        /* Non-transactional changes require a valid snapshot. */
        Assert(snapshot_now);
 
        if (xid != InvalidTransactionId)
            txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
 
        /* setup snapshot to allow catalog access */
        SetupHistoricSnapshot(snapshot_now, NULL);
        PG_TRY();
        {
            rb->message(rb, txn, lsn, false, prefix, message_size, message);
 
            TeardownHistoricSnapshot(false);
        }
        PG_CATCH();
        {
            TeardownHistoricSnapshot(true);
            PG_RE_THROW();
        }
        PG_END_TRY();
    }
}
 
/*
 * AssertTXNLsnOrder
 *      Verify LSN ordering of transaction lists in the reorderbuffer
 *
 * Other LSN-related invariants are checked too.
 *
 * No-op if assertions are not in use.
 */
static void
AssertTXNLsnOrder(ReorderBuffer *rb)
{
#ifdef USE_ASSERT_CHECKING
    LogicalDecodingContext *ctx = rb->private_data;
    dlist_iter  iter;
    XLogRecPtr  prev_first_lsn = InvalidXLogRecPtr;
    XLogRecPtr  prev_base_snap_lsn = InvalidXLogRecPtr;
 
    /*
     * Skip the verification if we don't reach the LSN at which we start
     * decoding the contents of transactions yet because until we reach the
     * LSN, we could have transactions that don't have the association between
     * the top-level transaction and subtransaction yet and consequently have
     * the same LSN.  We don't guarantee this association until we try to
     * decode the actual contents of transaction. The ordering of the records
     * prior to the start_decoding_at LSN should have been checked before the
     * restart.
     */
    if (SnapBuildXactNeedsSkip(ctx->snapshot_builder, ctx->reader->EndRecPtr))
        return;
 
    dlist_foreach(iter, &rb->toplevel_by_lsn)
    {
        ReorderBufferTXN *cur_txn = dlist_container(ReorderBufferTXN, node,
                                                    iter.cur);
 
        /* start LSN must be set */
        Assert(cur_txn->first_lsn != InvalidXLogRecPtr);
 
        /* If there is an end LSN, it must be higher than start LSN */
        if (cur_txn->end_lsn != InvalidXLogRecPtr)
            Assert(cur_txn->first_lsn <= cur_txn->end_lsn);
 
        /* Current initial LSN must be strictly higher than previous */
        if (prev_first_lsn != InvalidXLogRecPtr)
            Assert(prev_first_lsn < cur_txn->first_lsn);
 
        /* known-as-subtxn txns must not be listed */
        Assert(!rbtxn_is_known_subxact(cur_txn));
 
        prev_first_lsn = cur_txn->first_lsn;
    }
 
    dlist_foreach(iter, &rb->txns_by_base_snapshot_lsn)
    {
        ReorderBufferTXN *cur_txn = dlist_container(ReorderBufferTXN,
                                                    base_snapshot_node,
                                                    iter.cur);
 
        /* base snapshot (and its LSN) must be set */
        Assert(cur_txn->base_snapshot != NULL);
        Assert(cur_txn->base_snapshot_lsn != InvalidXLogRecPtr);
 
        /* current LSN must be strictly higher than previous */
        if (prev_base_snap_lsn != InvalidXLogRecPtr)
            Assert(prev_base_snap_lsn < cur_txn->base_snapshot_lsn);
 
        /* known-as-subtxn txns must not be listed */
        Assert(!rbtxn_is_known_subxact(cur_txn));
 
        prev_base_snap_lsn = cur_txn->base_snapshot_lsn;
    }
#endif
}
 
/*
 * AssertChangeLsnOrder
 *
 * Check ordering of changes in the (sub)transaction.
 */
static void
AssertChangeLsnOrder(ReorderBufferTXN *txn)
{
#ifdef USE_ASSERT_CHECKING
    dlist_iter  iter;
    XLogRecPtr  prev_lsn = txn->first_lsn;
 
    dlist_foreach(iter, &txn->changes)
    {
        ReorderBufferChange *cur_change;
 
        cur_change = dlist_container(ReorderBufferChange, node, iter.cur);
 
        Assert(txn->first_lsn != InvalidXLogRecPtr);
        Assert(cur_change->lsn != InvalidXLogRecPtr);
        Assert(txn->first_lsn <= cur_change->lsn);
 
        if (txn->end_lsn != InvalidXLogRecPtr)
            Assert(cur_change->lsn <= txn->end_lsn);
 
        Assert(prev_lsn <= cur_change->lsn);
 
        prev_lsn = cur_change->lsn;
    }
#endif
}
 
/*
 * ReorderBufferGetOldestTXN
 *      Return oldest transaction in reorderbuffer
 */
ReorderBufferTXN *
ReorderBufferGetOldestTXN(ReorderBuffer *rb)
{
    ReorderBufferTXN *txn;
 
    AssertTXNLsnOrder(rb);
 
    if (dlist_is_empty(&rb->toplevel_by_lsn))
        return NULL;
 
    txn = dlist_head_element(ReorderBufferTXN, node, &rb->toplevel_by_lsn);
 
    Assert(!rbtxn_is_known_subxact(txn));
    Assert(txn->first_lsn != InvalidXLogRecPtr);
    return txn;
}
 
/*
 * ReorderBufferGetOldestXmin
 *      Return oldest Xmin in reorderbuffer
 *
 * Returns oldest possibly running Xid from the point of view of snapshots
 * used in the transactions kept by reorderbuffer, or InvalidTransactionId if
 * there are none.
 *
 * Since snapshots are assigned monotonically, this equals the Xmin of the
 * base snapshot with minimal base_snapshot_lsn.
 */
TransactionId
ReorderBufferGetOldestXmin(ReorderBuffer *rb)
{
    ReorderBufferTXN *txn;
 
    AssertTXNLsnOrder(rb);
 
    if (dlist_is_empty(&rb->txns_by_base_snapshot_lsn))
        return InvalidTransactionId;
 
    txn = dlist_head_element(ReorderBufferTXN, base_snapshot_node,
                             &rb->txns_by_base_snapshot_lsn);
    return txn->base_snapshot->xmin;
}
 
void
ReorderBufferSetRestartPoint(ReorderBuffer *rb, XLogRecPtr ptr)
{
    rb->current_restart_decoding_lsn = ptr;
}
 
/*
 * ReorderBufferAssignChild
 *
 * Make note that we know that subxid is a subtransaction of xid, seen as of
 * the given lsn.
 */
void
ReorderBufferAssignChild(ReorderBuffer *rb, TransactionId xid,
                         TransactionId subxid, XLogRecPtr lsn)
{
    ReorderBufferTXN *txn;
    ReorderBufferTXN *subtxn;
    bool        new_top;
    bool        new_sub;
 
    txn = ReorderBufferTXNByXid(rb, xid, true, &new_top, lsn, true);
    subtxn = ReorderBufferTXNByXid(rb, subxid, true, &new_sub, lsn, false);
 
    if (!new_sub)
    {
        if (rbtxn_is_known_subxact(subtxn))
        {
            /* already associated, nothing to do */
            return;
        }
        else
        {
            /*
             * We already saw this transaction, but initially added it to the
             * list of top-level txns.  Now that we know it's not top-level,
             * remove it from there.
             */
            dlist_delete(&subtxn->node);
        }
    }
 
    subtxn->txn_flags |= RBTXN_IS_SUBXACT;
    subtxn->toplevel_xid = xid;
    Assert(subtxn->nsubtxns == 0);
 
    /* set the reference to top-level transaction */
    subtxn->toptxn = txn;
 
    /* add to subtransaction list */
    dlist_push_tail(&txn->subtxns, &subtxn->node);
    txn->nsubtxns++;
 
    /* Possibly transfer the subtxn's snapshot to its top-level txn. */
    ReorderBufferTransferSnapToParent(txn, subtxn);
 
    /* Verify LSN-ordering invariant */
    AssertTXNLsnOrder(rb);
}
 
/*
 * ReorderBufferTransferSnapToParent
 *      Transfer base snapshot from subtxn to top-level txn, if needed
 *
 * This is done if the top-level txn doesn't have a base snapshot, or if the
 * subtxn's base snapshot has an earlier LSN than the top-level txn's base
 * snapshot's LSN.  This can happen if there are no changes in the toplevel
 * txn but there are some in the subtxn, or the first change in subtxn has
 * earlier LSN than first change in the top-level txn and we learned about
 * their kinship only now.
 *
 * The subtransaction's snapshot is cleared regardless of the transfer
 * happening, since it's not needed anymore in either case.
 *
 * We do this as soon as we become aware of their kinship, to avoid queueing
 * extra snapshots to txns known-as-subtxns -- only top-level txns will
 * receive further snapshots.
 */
static void
ReorderBufferTransferSnapToParent(ReorderBufferTXN *txn,
                                  ReorderBufferTXN *subtxn)
{
    Assert(subtxn->toplevel_xid == txn->xid);
 
    if (subtxn->base_snapshot != NULL)
    {
        if (txn->base_snapshot == NULL ||
            subtxn->base_snapshot_lsn < txn->base_snapshot_lsn)
        {
            /*
             * If the toplevel transaction already has a base snapshot but
             * it's newer than the subxact's, purge it.
             */
            if (txn->base_snapshot != NULL)
            {
                SnapBuildSnapDecRefcount(txn->base_snapshot);
                dlist_delete(&txn->base_snapshot_node);
            }
 
            /*
             * The snapshot is now the top transaction's; transfer it, and
             * adjust the list position of the top transaction in the list by
             * moving it to where the subtransaction is.
             */
            txn->base_snapshot = subtxn->base_snapshot;
            txn->base_snapshot_lsn = subtxn->base_snapshot_lsn;
            dlist_insert_before(&subtxn->base_snapshot_node,
                                &txn->base_snapshot_node);
 
            /*
             * The subtransaction doesn't have a snapshot anymore (so it
             * mustn't be in the list.)
             */
            subtxn->base_snapshot = NULL;
            subtxn->base_snapshot_lsn = InvalidXLogRecPtr;
            dlist_delete(&subtxn->base_snapshot_node);
        }
        else
        {
            /* Base snap of toplevel is fine, so subxact's is not needed */
            SnapBuildSnapDecRefcount(subtxn->base_snapshot);
            dlist_delete(&subtxn->base_snapshot_node);
            subtxn->base_snapshot = NULL;
            subtxn->base_snapshot_lsn = InvalidXLogRecPtr;
        }
    }
}
 
/*
 * Associate a subtransaction with its toplevel transaction at commit
 * time. There may be no further changes added after this.
 */
void
ReorderBufferCommitChild(ReorderBuffer *rb, TransactionId xid,
                         TransactionId subxid, XLogRecPtr commit_lsn,
                         XLogRecPtr end_lsn)
{
    ReorderBufferTXN *subtxn;
 
    subtxn = ReorderBufferTXNByXid(rb, subxid, false, NULL,
                                   InvalidXLogRecPtr, false);
 
    /*
     * No need to do anything if that subtxn didn't contain any changes
     */
    if (!subtxn)
        return;
 
    subtxn->final_lsn = commit_lsn;
    subtxn->end_lsn = end_lsn;
 
    /*
     * Assign this subxact as a child of the toplevel xact (no-op if already
     * done.)
     */
    ReorderBufferAssignChild(rb, xid, subxid, InvalidXLogRecPtr);
}
 
 
/*
 * Support for efficiently iterating over a transaction's and its
 * subtransactions' changes.
 *
 * We do by doing a k-way merge between transactions/subtransactions. For that
 * we model the current heads of the different transactions as a binary heap
 * so we easily know which (sub-)transaction has the change with the smallest
 * lsn next.
 *
 * We assume the changes in individual transactions are already sorted by LSN.
 */
 
/*
 * Binary heap comparison function.
 */
static int
ReorderBufferIterCompare(Datum a, Datum b, void *arg)
{
    ReorderBufferIterTXNState *state = (ReorderBufferIterTXNState *) arg;
    XLogRecPtr  pos_a = state->entries[DatumGetInt32(a)].lsn;
    XLogRecPtr  pos_b = state->entries[DatumGetInt32(b)].lsn;
 
    if (pos_a < pos_b)
        return 1;
    else if (pos_a == pos_b)
        return 0;
    return -1;
}
 
/*
 * Allocate & initialize an iterator which iterates in lsn order over a
 * transaction and all its subtransactions.
 *
 * Note: The iterator state is returned through iter_state parameter rather
 * than the function's return value.  This is because the state gets cleaned up
 * in a PG_CATCH block in the caller, so we want to make sure the caller gets
 * back the state even if this function throws an exception.
 */
static void
ReorderBufferIterTXNInit(ReorderBuffer *rb, ReorderBufferTXN *txn,
                         ReorderBufferIterTXNState *volatile *iter_state)
{
    Size        nr_txns = 0;
    ReorderBufferIterTXNState *state;
    dlist_iter  cur_txn_i;
    int32       off;
 
    *iter_state = NULL;
 
    /* Check ordering of changes in the toplevel transaction. */
    AssertChangeLsnOrder(txn);
 
    /*
     * Calculate the size of our heap: one element for every transaction that
     * contains changes.  (Besides the transactions already in the reorder
     * buffer, we count the one we were directly passed.)
     */
    if (txn->nentries > 0)
        nr_txns++;
 
    dlist_foreach(cur_txn_i, &txn->subtxns)
    {
        ReorderBufferTXN *cur_txn;
 
        cur_txn = dlist_container(ReorderBufferTXN, node, cur_txn_i.cur);
 
        /* Check ordering of changes in this subtransaction. */
        AssertChangeLsnOrder(cur_txn);
 
        if (cur_txn->nentries > 0)
            nr_txns++;
    }
 
    /* allocate iteration state */
    state = (ReorderBufferIterTXNState *)
        MemoryContextAllocZero(rb->context,
                               sizeof(ReorderBufferIterTXNState) +
                               sizeof(ReorderBufferIterTXNEntry) * nr_txns);
 
    state->nr_txns = nr_txns;
    dlist_init(&state->old_change);
 
    for (off = 0; off < state->nr_txns; off++)
    {
        state->entries[off].file.vfd = -1;
        state->entries[off].segno = 0;
    }
 
    /* allocate heap */
    state->heap = binaryheap_allocate(state->nr_txns,
                                      ReorderBufferIterCompare,
                                      state);
 
    /* Now that the state fields are initialized, it is safe to return it. */
    *iter_state = state;
 
    /*
     * Now insert items into the binary heap, in an unordered fashion.  (We
     * will run a heap assembly step at the end; this is more efficient.)
     */
 
    off = 0;
 
    /* add toplevel transaction if it contains changes */
    if (txn->nentries > 0)
    {
        ReorderBufferChange *cur_change;
 
        if (rbtxn_is_serialized(txn))
        {
            /* serialize remaining changes */
            ReorderBufferSerializeTXN(rb, txn);
            ReorderBufferRestoreChanges(rb, txn, &state->entries[off].file,
                                        &state->entries[off].segno);
        }
 
        cur_change = dlist_head_element(ReorderBufferChange, node,
                                        &txn->changes);
 
        state->entries[off].lsn = cur_change->lsn;
        state->entries[off].change = cur_change;
        state->entries[off].txn = txn;
 
        binaryheap_add_unordered(state->heap, Int32GetDatum(off++));
    }
 
    /* add subtransactions if they contain changes */
    dlist_foreach(cur_txn_i, &txn->subtxns)
    {
        ReorderBufferTXN *cur_txn;
 
        cur_txn = dlist_container(ReorderBufferTXN, node, cur_txn_i.cur);
 
        if (cur_txn->nentries > 0)
        {
            ReorderBufferChange *cur_change;
 
            if (rbtxn_is_serialized(cur_txn))
            {
                /* serialize remaining changes */
                ReorderBufferSerializeTXN(rb, cur_txn);
                ReorderBufferRestoreChanges(rb, cur_txn,
                                            &state->entries[off].file,
                                            &state->entries[off].segno);
            }
            cur_change = dlist_head_element(ReorderBufferChange, node,
                                            &cur_txn->changes);
 
            state->entries[off].lsn = cur_change->lsn;
            state->entries[off].change = cur_change;
            state->entries[off].txn = cur_txn;
 
            binaryheap_add_unordered(state->heap, Int32GetDatum(off++));
        }
    }
 
    /* assemble a valid binary heap */
    binaryheap_build(state->heap);
}
 
/*
 * Return the next change when iterating over a transaction and its
 * subtransactions.
 *
 * Returns NULL when no further changes exist.
 */
static ReorderBufferChange *
ReorderBufferIterTXNNext(ReorderBuffer *rb, ReorderBufferIterTXNState *state)
{
    ReorderBufferChange *change;
    ReorderBufferIterTXNEntry *entry;
    int32       off;
 
    /* nothing there anymore */
    if (state->heap->bh_size == 0)
        return NULL;
 
    off = DatumGetInt32(binaryheap_first(state->heap));
    entry = &state->entries[off];
 
    /* free memory we might have "leaked" in the previous *Next call */
    if (!dlist_is_empty(&state->old_change))
    {
        change = dlist_container(ReorderBufferChange, node,
                                 dlist_pop_head_node(&state->old_change));
        ReorderBufferReturnChange(rb, change, true);
        Assert(dlist_is_empty(&state->old_change));
    }
 
    change = entry->change;
 
    /*
     * update heap with information about which transaction has the next
     * relevant change in LSN order
     */
 
    /* there are in-memory changes */
    if (dlist_has_next(&entry->txn->changes, &entry->change->node))
    {
        dlist_node *next = dlist_next_node(&entry->txn->changes, &change->node);
        ReorderBufferChange *next_change =
            dlist_container(ReorderBufferChange, node, next);
 
        /* txn stays the same */
        state->entries[off].lsn = next_change->lsn;
        state->entries[off].change = next_change;
 
        binaryheap_replace_first(state->heap, Int32GetDatum(off));
        return change;
    }
 
    /* try to load changes from disk */
    if (entry->txn->nentries != entry->txn->nentries_mem)
    {
        /*
         * Ugly: restoring changes will reuse *Change records, thus delete the
         * current one from the per-tx list and only free in the next call.
         */
        dlist_delete(&change->node);
        dlist_push_tail(&state->old_change, &change->node);
 
        /*
         * Update the total bytes processed by the txn for which we are
         * releasing the current set of changes and restoring the new set of
         * changes.
         */
        rb->totalBytes += entry->txn->size;
        if (ReorderBufferRestoreChanges(rb, entry->txn, &entry->file,
                                        &state->entries[off].segno))
        {
            /* successfully restored changes from disk */
            ReorderBufferChange *next_change =
                dlist_head_element(ReorderBufferChange, node,
                                   &entry->txn->changes);
 
            elog(DEBUG2, "restored %u/%u changes from disk",
                 (uint32) entry->txn->nentries_mem,
                 (uint32) entry->txn->nentries);
 
            Assert(entry->txn->nentries_mem);
            /* txn stays the same */
            state->entries[off].lsn = next_change->lsn;
            state->entries[off].change = next_change;
            binaryheap_replace_first(state->heap, Int32GetDatum(off));
 
            return change;
        }
    }
 
    /* ok, no changes there anymore, remove */
    binaryheap_remove_first(state->heap);
 
    return change;
}
 
/*
 * Deallocate the iterator
 */
static void
ReorderBufferIterTXNFinish(ReorderBuffer *rb,
                           ReorderBufferIterTXNState *state)
{
    int32       off;
 
    for (off = 0; off < state->nr_txns; off++)
    {
        if (state->entries[off].file.vfd != -1)
            FileClose(state->entries[off].file.vfd);
    }
 
    /* free memory we might have "leaked" in the last *Next call */
    if (!dlist_is_empty(&state->old_change))
    {
        ReorderBufferChange *change;
 
        change = dlist_container(ReorderBufferChange, node,
                                 dlist_pop_head_node(&state->old_change));
        ReorderBufferReturnChange(rb, change, true);
        Assert(dlist_is_empty(&state->old_change));
    }
 
    binaryheap_free(state->heap);
    pfree(state);
}
 
/*
 * Cleanup the contents of a transaction, usually after the transaction
 * committed or aborted.
 */
static void
ReorderBufferCleanupTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
{
    bool        found;
    dlist_mutable_iter iter;
    Size        mem_freed = 0;
 
    /* cleanup subtransactions & their changes */
    dlist_foreach_modify(iter, &txn->subtxns)
    {
        ReorderBufferTXN *subtxn;
 
        subtxn = dlist_container(ReorderBufferTXN, node, iter.cur);
 
        /*
         * Subtransactions are always associated to the toplevel TXN, even if
         * they originally were happening inside another subtxn, so we won't
         * ever recurse more than one level deep here.
         */
        Assert(rbtxn_is_known_subxact(subtxn));
        Assert(subtxn->nsubtxns == 0);
 
        ReorderBufferCleanupTXN(rb, subtxn);
    }
 
    /* cleanup changes in the txn */
    dlist_foreach_modify(iter, &txn->changes)
    {
        ReorderBufferChange *change;
 
        change = dlist_container(ReorderBufferChange, node, iter.cur);
 
        /* Check we're not mixing changes from different transactions. */
        Assert(change->txn == txn);
 
        /*
         * Instead of updating the memory counter for individual changes, we
         * sum up the size of memory to free so we can update the memory
         * counter all together below. This saves costs of maintaining the
         * max-heap.
         */
        mem_freed += ReorderBufferChangeSize(change);
 
        ReorderBufferReturnChange(rb, change, false);
    }
 
    /* Update the memory counter */
    ReorderBufferChangeMemoryUpdate(rb, NULL, txn, false, mem_freed);
 
    /*
     * Cleanup the tuplecids we stored for decoding catalog snapshot access.
     * They are always stored in the toplevel transaction.
     */
    dlist_foreach_modify(iter, &txn->tuplecids)
    {
        ReorderBufferChange *change;
 
        change = dlist_container(ReorderBufferChange, node, iter.cur);
 
        /* Check we're not mixing changes from different transactions. */
        Assert(change->txn == txn);
        Assert(change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
 
        ReorderBufferReturnChange(rb, change, true);
    }
 
    /*
     * Cleanup the base snapshot, if set.
     */
    if (txn->base_snapshot != NULL)
    {
        SnapBuildSnapDecRefcount(txn->base_snapshot);
        dlist_delete(&txn->base_snapshot_node);
    }
 
    /*
     * Cleanup the snapshot for the last streamed run.
     */
    if (txn->snapshot_now != NULL)
    {
        Assert(rbtxn_is_streamed(txn));
        ReorderBufferFreeSnap(rb, txn->snapshot_now);
    }
 
    /*
     * Remove TXN from its containing lists.
     *
     * Note: if txn is known as subxact, we are deleting the TXN from its
     * parent's list of known subxacts; this leaves the parent's nsubxacts
     * count too high, but we don't care.  Otherwise, we are deleting the TXN
     * from the LSN-ordered list of toplevel TXNs. We remove the TXN from the
     * list of catalog modifying transactions as well.
     */
    dlist_delete(&txn->node);
    if (rbtxn_has_catalog_changes(txn))
        dclist_delete_from(&rb->catchange_txns, &txn->catchange_node);
 
    /* now remove reference from buffer */
    hash_search(rb->by_txn, &txn->xid, HASH_REMOVE, &found);
    Assert(found);
 
    /* remove entries spilled to disk */
    if (rbtxn_is_serialized(txn))
        ReorderBufferRestoreCleanup(rb, txn);
 
    /* deallocate */
    ReorderBufferReturnTXN(rb, txn);
}
 
/*
 * Discard changes from a transaction (and subtransactions), either after
 * streaming or decoding them at PREPARE. Keep the remaining info -
 * transactions, tuplecids, invalidations and snapshots.
 *
 * We additionally remove tuplecids after decoding the transaction at prepare
 * time as we only need to perform invalidation at rollback or commit prepared.
 *
 * 'txn_prepared' indicates that we have decoded the transaction at prepare
 * time.
 */
static void
ReorderBufferTruncateTXN(ReorderBuffer *rb, ReorderBufferTXN *txn, bool txn_prepared)
{
    dlist_mutable_iter iter;
    Size        mem_freed = 0;
 
    /* cleanup subtransactions & their changes */
    dlist_foreach_modify(iter, &txn->subtxns)
    {
        ReorderBufferTXN *subtxn;
 
        subtxn = dlist_container(ReorderBufferTXN, node, iter.cur);
 
        /*
         * Subtransactions are always associated to the toplevel TXN, even if
         * they originally were happening inside another subtxn, so we won't
         * ever recurse more than one level deep here.
         */
        Assert(rbtxn_is_known_subxact(subtxn));
        Assert(subtxn->nsubtxns == 0);
 
        ReorderBufferTruncateTXN(rb, subtxn, txn_prepared);
    }
 
    /* cleanup changes in the txn */
    dlist_foreach_modify(iter, &txn->changes)
    {
        ReorderBufferChange *change;
 
        change = dlist_container(ReorderBufferChange, node, iter.cur);
 
        /* Check we're not mixing changes from different transactions. */
        Assert(change->txn == txn);
 
        /* remove the change from it's containing list */
        dlist_delete(&change->node);
 
        /*
         * Instead of updating the memory counter for individual changes, we
         * sum up the size of memory to free so we can update the memory
         * counter all together below. This saves costs of maintaining the
         * max-heap.
         */
        mem_freed += ReorderBufferChangeSize(change);
 
        ReorderBufferReturnChange(rb, change, false);
    }
 
    /* Update the memory counter */
    ReorderBufferChangeMemoryUpdate(rb, NULL, txn, false, mem_freed);
 
    /*
     * Mark the transaction as streamed.
     *
     * The top-level transaction, is marked as streamed always, even if it
     * does not contain any changes (that is, when all the changes are in
     * subtransactions).
     *
     * For subtransactions, we only mark them as streamed when there are
     * changes in them.
     *
     * We do it this way because of aborts - we don't want to send aborts for
     * XIDs the downstream is not aware of. And of course, it always knows
     * about the toplevel xact (we send the XID in all messages), but we never
     * stream XIDs of empty subxacts.
     */
    if ((!txn_prepared) && (rbtxn_is_toptxn(txn) || (txn->nentries_mem != 0)))
        txn->txn_flags |= RBTXN_IS_STREAMED;
 
    if (txn_prepared)
    {
        /*
         * If this is a prepared txn, cleanup the tuplecids we stored for
         * decoding catalog snapshot access. They are always stored in the
         * toplevel transaction.
         */
        dlist_foreach_modify(iter, &txn->tuplecids)
        {
            ReorderBufferChange *change;
 
            change = dlist_container(ReorderBufferChange, node, iter.cur);
 
            /* Check we're not mixing changes from different transactions. */
            Assert(change->txn == txn);
            Assert(change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
 
            /* Remove the change from its containing list. */
            dlist_delete(&change->node);
 
            ReorderBufferReturnChange(rb, change, true);
        }
    }
 
    /*
     * Destroy the (relfilelocator, ctid) hashtable, so that we don't leak any
     * memory. We could also keep the hash table and update it with new ctid
     * values, but this seems simpler and good enough for now.
     */
    if (txn->tuplecid_hash != NULL)
    {
        hash_destroy(txn->tuplecid_hash);
        txn->tuplecid_hash = NULL;
    }
 
    /* If this txn is serialized then clean the disk space. */
    if (rbtxn_is_serialized(txn))
    {
        ReorderBufferRestoreCleanup(rb, txn);
        txn->txn_flags &= ~RBTXN_IS_SERIALIZED;
 
        /*
         * We set this flag to indicate if the transaction is ever serialized.
         * We need this to accurately update the stats as otherwise the same
         * transaction can be counted as serialized multiple times.
         */
        txn->txn_flags |= RBTXN_IS_SERIALIZED_CLEAR;
    }
 
    /* also reset the number of entries in the transaction */
    txn->nentries_mem = 0;
    txn->nentries = 0;
}
 
/*
 * Build a hash with a (relfilelocator, ctid) -> (cmin, cmax) mapping for use by
 * HeapTupleSatisfiesHistoricMVCC.
 */
static void
ReorderBufferBuildTupleCidHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
{
    dlist_iter  iter;
    HASHCTL     hash_ctl;
 
    if (!rbtxn_has_catalog_changes(txn) || dlist_is_empty(&txn->tuplecids))
        return;
 
    hash_ctl.keysize = sizeof(ReorderBufferTupleCidKey);
    hash_ctl.entrysize = sizeof(ReorderBufferTupleCidEnt);
    hash_ctl.hcxt = rb->context;
 
    /*
     * create the hash with the exact number of to-be-stored tuplecids from
     * the start
     */
    txn->tuplecid_hash =
        hash_create("ReorderBufferTupleCid", txn->ntuplecids, &hash_ctl,
                    HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
 
    dlist_foreach(iter, &txn->tuplecids)
    {
        ReorderBufferTupleCidKey key;
        ReorderBufferTupleCidEnt *ent;
        bool        found;
        ReorderBufferChange *change;
 
        change = dlist_container(ReorderBufferChange, node, iter.cur);
 
        Assert(change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
 
        /* be careful about padding */
        memset(&key, 0, sizeof(ReorderBufferTupleCidKey));
 
        key.rlocator = change->data.tuplecid.locator;
 
        ItemPointerCopy(&change->data.tuplecid.tid,
                        &key.tid);
 
        ent = (ReorderBufferTupleCidEnt *)
            hash_search(txn->tuplecid_hash, &key, HASH_ENTER, &found);
        if (!found)
        {
            ent->cmin = change->data.tuplecid.cmin;
            ent->cmax = change->data.tuplecid.cmax;
            ent->combocid = change->data.tuplecid.combocid;
        }
        else
        {
            /*
             * Maybe we already saw this tuple before in this transaction, but
             * if so it must have the same cmin.
             */
            Assert(ent->cmin == change->data.tuplecid.cmin);
 
            /*
             * cmax may be initially invalid, but once set it can only grow,
             * and never become invalid again.
             */
            Assert((ent->cmax == InvalidCommandId) ||
                   ((change->data.tuplecid.cmax != InvalidCommandId) &&
                    (change->data.tuplecid.cmax > ent->cmax)));
            ent->cmax = change->data.tuplecid.cmax;
        }
    }
}
 
/*
 * Copy a provided snapshot so we can modify it privately. This is needed so
 * that catalog modifying transactions can look into intermediate catalog
 * states.
 */
static Snapshot
ReorderBufferCopySnap(ReorderBuffer *rb, Snapshot orig_snap,
                      ReorderBufferTXN *txn, CommandId cid)
{
    Snapshot    snap;
    dlist_iter  iter;
    int         i = 0;
    Size        size;
 
    size = sizeof(SnapshotData) +
        sizeof(TransactionId) * orig_snap->xcnt +
        sizeof(TransactionId) * (txn->nsubtxns + 1);
 
    snap = MemoryContextAllocZero(rb->context, size);
    memcpy(snap, orig_snap, sizeof(SnapshotData));
 
    snap->copied = true;
    snap->active_count = 1;     /* mark as active so nobody frees it */
    snap->regd_count = 0;
    snap->xip = (TransactionId *) (snap + 1);
 
    memcpy(snap->xip, orig_snap->xip, sizeof(TransactionId) * snap->xcnt);
 
    /*
     * snap->subxip contains all txids that belong to our transaction which we
     * need to check via cmin/cmax. That's why we store the toplevel
     * transaction in there as well.
     */
    snap->subxip = snap->xip + snap->xcnt;
    snap->subxip[i++] = txn->xid;
 
    /*
     * subxcnt isn't decreased when subtransactions abort, so count manually.
     * Since it's an upper boundary it is safe to use it for the allocation
     * above.
     */
    snap->subxcnt = 1;
 
    dlist_foreach(iter, &txn->subtxns)
    {
        ReorderBufferTXN *sub_txn;
 
        sub_txn = dlist_container(ReorderBufferTXN, node, iter.cur);
        snap->subxip[i++] = sub_txn->xid;
        snap->subxcnt++;
    }
 
    /* sort so we can bsearch() later */
    qsort(snap->subxip, snap->subxcnt, sizeof(TransactionId), xidComparator);
 
    /* store the specified current CommandId */
    snap->curcid = cid;
 
    return snap;
}
 
/*
 * Free a previously ReorderBufferCopySnap'ed snapshot
 */
static void
ReorderBufferFreeSnap(ReorderBuffer *rb, Snapshot snap)
{
    if (snap->copied)
        pfree(snap);
    else
        SnapBuildSnapDecRefcount(snap);
}
 
/*
 * If the transaction was (partially) streamed, we need to prepare or commit
 * it in a 'streamed' way.  That is, we first stream the remaining part of the
 * transaction, and then invoke stream_prepare or stream_commit message as per
 * the case.
 */
static void
ReorderBufferStreamCommit(ReorderBuffer *rb, ReorderBufferTXN *txn)
{
    /* we should only call this for previously streamed transactions */
    Assert(rbtxn_is_streamed(txn));
 
    ReorderBufferStreamTXN(rb, txn);
 
    if (rbtxn_prepared(txn))
    {
        /*
         * Note, we send stream prepare even if a concurrent abort is
         * detected. See DecodePrepare for more information.
         */
        rb->stream_prepare(rb, txn, txn->final_lsn);
 
        /*
         * This is a PREPARED transaction, part of a two-phase commit. The
         * full cleanup will happen as part of the COMMIT PREPAREDs, so now
         * just truncate txn by removing changes and tuplecids.
         */
        ReorderBufferTruncateTXN(rb, txn, true);
        /* Reset the CheckXidAlive */
        CheckXidAlive = InvalidTransactionId;
    }
    else
    {
        rb->stream_commit(rb, txn, txn->final_lsn);
        ReorderBufferCleanupTXN(rb, txn);
    }
}
 
/*
 * Set xid to detect concurrent aborts.
 *
 * While streaming an in-progress transaction or decoding a prepared
 * transaction there is a possibility that the (sub)transaction might get
 * aborted concurrently.  In such case if the (sub)transaction has catalog
 * update then we might decode the tuple using wrong catalog version.  For
 * example, suppose there is one catalog tuple with (xmin: 500, xmax: 0).  Now,
 * the transaction 501 updates the catalog tuple and after that we will have
 * two tuples (xmin: 500, xmax: 501) and (xmin: 501, xmax: 0).  Now, if 501 is
 * aborted and some other transaction say 502 updates the same catalog tuple
 * then the first tuple will be changed to (xmin: 500, xmax: 502).  So, the
 * problem is that when we try to decode the tuple inserted/updated in 501
 * after the catalog update, we will see the catalog tuple with (xmin: 500,
 * xmax: 502) as visible because it will consider that the tuple is deleted by
 * xid 502 which is not visible to our snapshot.  And when we will try to
 * decode with that catalog tuple, it can lead to a wrong result or a crash.
 * So, it is necessary to detect concurrent aborts to allow streaming of
 * in-progress transactions or decoding of prepared transactions.
 *
 * For detecting the concurrent abort we set CheckXidAlive to the current
 * (sub)transaction's xid for which this change belongs to.  And, during
 * catalog scan we can check the status of the xid and if it is aborted we will
 * report a specific error so that we can stop streaming current transaction
 * and discard the already streamed changes on such an error.  We might have
 * already streamed some of the changes for the aborted (sub)transaction, but
 * that is fine because when we decode the abort we will stream abort message
 * to truncate the changes in the subscriber. Similarly, for prepared
 * transactions, we stop decoding if concurrent abort is detected and then
 * rollback the changes when rollback prepared is encountered. See
 * DecodePrepare.
 */
static inline void
SetupCheckXidLive(TransactionId xid)
{
    /*
     * If the input transaction id is already set as a CheckXidAlive then
     * nothing to do.
     */
    if (TransactionIdEquals(CheckXidAlive, xid))
        return;
 
    /*
     * setup CheckXidAlive if it's not committed yet.  We don't check if the
     * xid is aborted.  That will happen during catalog access.
     */
    if (!TransactionIdDidCommit(xid))
        CheckXidAlive = xid;
    else
        CheckXidAlive = InvalidTransactionId;
}
 
/*
 * Helper function for ReorderBufferProcessTXN for applying change.
 */
static inline void
ReorderBufferApplyChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
                         Relation relation, ReorderBufferChange *change,
                         bool streaming)
{
    if (streaming)
        rb->stream_change(rb, txn, relation, change);
    else
        rb->apply_change(rb, txn, relation, change);
}
 
/*
 * Helper function for ReorderBufferProcessTXN for applying the truncate.
 */
static inline void
ReorderBufferApplyTruncate(ReorderBuffer *rb, ReorderBufferTXN *txn,
                           int nrelations, Relation *relations,
                           ReorderBufferChange *change, bool streaming)
{
    if (streaming)
        rb->stream_truncate(rb, txn, nrelations, relations, change);
    else
        rb->apply_truncate(rb, txn, nrelations, relations, change);
}
 
/*
 * Helper function for ReorderBufferProcessTXN for applying the message.
 */
static inline void
ReorderBufferApplyMessage(ReorderBuffer *rb, ReorderBufferTXN *txn,
                          ReorderBufferChange *change, bool streaming)
{
    if (streaming)
        rb->stream_message(rb, txn, change->lsn, true,
                           change->data.msg.prefix,
                           change->data.msg.message_size,
                           change->data.msg.message);
    else
        rb->message(rb, txn, change->lsn, true,
                    change->data.msg.prefix,
                    change->data.msg.message_size,
                    change->data.msg.message);
}
 
/*
 * Function to store the command id and snapshot at the end of the current
 * stream so that we can reuse the same while sending the next stream.
 */
static inline void
ReorderBufferSaveTXNSnapshot(ReorderBuffer *rb, ReorderBufferTXN *txn,
                             Snapshot snapshot_now, CommandId command_id)
{
    txn->command_id = command_id;
 
    /* Avoid copying if it's already copied. */
    if (snapshot_now->copied)
        txn->snapshot_now = snapshot_now;
    else
        txn->snapshot_now = ReorderBufferCopySnap(rb, snapshot_now,
                                                  txn, command_id);
}
 
/*
 * Helper function for ReorderBufferProcessTXN to handle the concurrent
 * abort of the streaming transaction.  This resets the TXN such that it
 * can be used to stream the remaining data of transaction being processed.
 * This can happen when the subtransaction is aborted and we still want to
 * continue processing the main or other subtransactions data.
 */
static void
ReorderBufferResetTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
                      Snapshot snapshot_now,
                      CommandId command_id,
                      XLogRecPtr last_lsn,
                      ReorderBufferChange *specinsert)
{
    /* Discard the changes that we just streamed */
    ReorderBufferTruncateTXN(rb, txn, rbtxn_prepared(txn));
 
    /* Free all resources allocated for toast reconstruction */
    ReorderBufferToastReset(rb, txn);
 
    /* Return the spec insert change if it is not NULL */
    if (specinsert != NULL)
    {
        ReorderBufferReturnChange(rb, specinsert, true);
        specinsert = NULL;
    }
 
    /*
     * For the streaming case, stop the stream and remember the command ID and
     * snapshot for the streaming run.
     */
    if (rbtxn_is_streamed(txn))
    {
        rb->stream_stop(rb, txn, last_lsn);
        ReorderBufferSaveTXNSnapshot(rb, txn, snapshot_now, command_id);
    }
 
    /* All changes must be deallocated */
    Assert(txn->size == 0);
}
 
/*
 * Helper function for ReorderBufferReplay and ReorderBufferStreamTXN.
 *
 * Send data of a transaction (and its subtransactions) to the
 * output plugin. We iterate over the top and subtransactions (using a k-way
 * merge) and replay the changes in lsn order.
 *
 * If streaming is true then data will be sent using stream API.
 *
 * Note: "volatile" markers on some parameters are to avoid trouble with
 * PG_TRY inside the function.
 */
static void
ReorderBufferProcessTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
                        XLogRecPtr commit_lsn,
                        volatile Snapshot snapshot_now,
                        volatile CommandId command_id,
                        bool streaming)
{
    bool        using_subtxn;
    MemoryContext ccxt = CurrentMemoryContext;
    ReorderBufferIterTXNState *volatile iterstate = NULL;
    volatile XLogRecPtr prev_lsn = InvalidXLogRecPtr;
    ReorderBufferChange *volatile specinsert = NULL;
    volatile bool stream_started = false;
    ReorderBufferTXN *volatile curtxn = NULL;
 
    /* build data to be able to lookup the CommandIds of catalog tuples */
    ReorderBufferBuildTupleCidHash(rb, txn);
 
    /* setup the initial snapshot */
    SetupHistoricSnapshot(snapshot_now, txn->tuplecid_hash);
 
    /*
     * Decoding needs access to syscaches et al., which in turn use
     * heavyweight locks and such. Thus we need to have enough state around to
     * keep track of those.  The easiest way is to simply use a transaction
     * internally.  That also allows us to easily enforce that nothing writes
     * to the database by checking for xid assignments.
     *
     * When we're called via the SQL SRF there's already a transaction
     * started, so start an explicit subtransaction there.
     */
    using_subtxn = IsTransactionOrTransactionBlock();
 
    PG_TRY();
    {
        ReorderBufferChange *change;
        int         changes_count = 0;  /* used to accumulate the number of
                                         * changes */
 
        if (using_subtxn)
            BeginInternalSubTransaction(streaming ? "stream" : "replay");
        else
            StartTransactionCommand();
 
        /*
         * We only need to send begin/begin-prepare for non-streamed
         * transactions.
         */
        if (!streaming)
        {
            if (rbtxn_prepared(txn))
                rb->begin_prepare(rb, txn);
            else
                rb->begin(rb, txn);
        }
 
        ReorderBufferIterTXNInit(rb, txn, &iterstate);
        while ((change = ReorderBufferIterTXNNext(rb, iterstate)) != NULL)
        {
            Relation    relation = NULL;
            Oid         reloid;
 
            CHECK_FOR_INTERRUPTS();
 
            /*
             * We can't call start stream callback before processing first
             * change.
             */
            if (prev_lsn == InvalidXLogRecPtr)
            {
                if (streaming)
                {
                    txn->origin_id = change->origin_id;
                    rb->stream_start(rb, txn, change->lsn);
                    stream_started = true;
                }
            }
 
            /*
             * Enforce correct ordering of changes, merged from multiple
             * subtransactions. The changes may have the same LSN due to
             * MULTI_INSERT xlog records.
             */
            Assert(prev_lsn == InvalidXLogRecPtr || prev_lsn <= change->lsn);
 
            prev_lsn = change->lsn;
 
            /*
             * Set the current xid to detect concurrent aborts. This is
             * required for the cases when we decode the changes before the
             * COMMIT record is processed.
             */
            if (streaming || rbtxn_prepared(change->txn))
            {
                curtxn = change->txn;
                SetupCheckXidLive(curtxn->xid);
            }
 
            switch (change->action)
            {
                case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
 
                    /*
                     * Confirmation for speculative insertion arrived. Simply
                     * use as a normal record. It'll be cleaned up at the end
                     * of INSERT processing.
                     */
                    if (specinsert == NULL)
                        elog(ERROR, "invalid ordering of speculative insertion changes");
                    Assert(specinsert->data.tp.oldtuple == NULL);
                    change = specinsert;
                    change->action = REORDER_BUFFER_CHANGE_INSERT;
 
                    /* intentionally fall through */
                case REORDER_BUFFER_CHANGE_INSERT:
                case REORDER_BUFFER_CHANGE_UPDATE:
                case REORDER_BUFFER_CHANGE_DELETE:
                    Assert(snapshot_now);
 
                    reloid = RelidByRelfilenumber(change->data.tp.rlocator.spcOid,
                                                  change->data.tp.rlocator.relNumber);
 
                    /*
                     * Mapped catalog tuple without data, emitted while
                     * catalog table was in the process of being rewritten. We
                     * can fail to look up the relfilenumber, because the
                     * relmapper has no "historic" view, in contrast to the
                     * normal catalog during decoding. Thus repeated rewrites
                     * can cause a lookup failure. That's OK because we do not
                     * decode catalog changes anyway. Normally such tuples
                     * would be skipped over below, but we can't identify
                     * whether the table should be logically logged without
                     * mapping the relfilenumber to the oid.
                     */
                    if (reloid == InvalidOid &&
                        change->data.tp.newtuple == NULL &&
                        change->data.tp.oldtuple == NULL)
                        goto change_done;
                    else if (reloid == InvalidOid)
                        elog(ERROR, "could not map filenumber \"%s\" to relation OID",
                             relpathperm(change->data.tp.rlocator,
                                         MAIN_FORKNUM));
 
                    relation = RelationIdGetRelation(reloid);
 
                    if (!RelationIsValid(relation))
                        elog(ERROR, "could not open relation with OID %u (for filenumber \"%s\")",
                             reloid,
                             relpathperm(change->data.tp.rlocator,
                                         MAIN_FORKNUM));
 
                    if (!RelationIsLogicallyLogged(relation))
                        goto change_done;
 
                    /*
                     * Ignore temporary heaps created during DDL unless the
                     * plugin has asked for them.
                     */
                    if (relation->rd_rel->relrewrite && !rb->output_rewrites)
                        goto change_done;
 
                    /*
                     * For now ignore sequence changes entirely. Most of the
                     * time they don't log changes using records we
                     * understand, so it doesn't make sense to handle the few
                     * cases we do.
                     */
                    if (relation->rd_rel->relkind == RELKIND_SEQUENCE)
                        goto change_done;
 
                    /* user-triggered change */
                    if (!IsToastRelation(relation))
                    {
                        ReorderBufferToastReplace(rb, txn, relation, change);
                        ReorderBufferApplyChange(rb, txn, relation, change,
                                                 streaming);
 
                        /*
                         * Only clear reassembled toast chunks if we're sure
                         * they're not required anymore. The creator of the
                         * tuple tells us.
                         */
                        if (change->data.tp.clear_toast_afterwards)
                            ReorderBufferToastReset(rb, txn);
                    }
                    /* we're not interested in toast deletions */
                    else if (change->action == REORDER_BUFFER_CHANGE_INSERT)
                    {
                        /*
                         * Need to reassemble the full toasted Datum in
                         * memory, to ensure the chunks don't get reused till
                         * we're done remove it from the list of this
                         * transaction's changes. Otherwise it will get
                         * freed/reused while restoring spooled data from
                         * disk.
                         */
                        Assert(change->data.tp.newtuple != NULL);
 
                        dlist_delete(&change->node);
                        ReorderBufferToastAppendChunk(rb, txn, relation,
                                                      change);
                    }
 
            change_done:
 
                    /*
                     * If speculative insertion was confirmed, the record
                     * isn't needed anymore.
                     */
                    if (specinsert != NULL)
                    {
                        ReorderBufferReturnChange(rb, specinsert, true);
                        specinsert = NULL;
                    }
 
                    if (RelationIsValid(relation))
                    {
                        RelationClose(relation);
                        relation = NULL;
                    }
                    break;
 
                case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
 
                    /*
                     * Speculative insertions are dealt with by delaying the
                     * processing of the insert until the confirmation record
                     * arrives. For that we simply unlink the record from the
                     * chain, so it does not get freed/reused while restoring
                     * spooled data from disk.
                     *
                     * This is safe in the face of concurrent catalog changes
                     * because the relevant relation can't be changed between
                     * speculative insertion and confirmation due to
                     * CheckTableNotInUse() and locking.
                     */
 
                    /* clear out a pending (and thus failed) speculation */
                    if (specinsert != NULL)
                    {
                        ReorderBufferReturnChange(rb, specinsert, true);
                        specinsert = NULL;
                    }
 
                    /* and memorize the pending insertion */
                    dlist_delete(&change->node);
                    specinsert = change;
                    break;
 
                case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
 
                    /*
                     * Abort for speculative insertion arrived. So cleanup the
                     * specinsert tuple and toast hash.
                     *
                     * Note that we get the spec abort change for each toast
                     * entry but we need to perform the cleanup only the first
                     * time we get it for the main table.
                     */
                    if (specinsert != NULL)
                    {
                        /*
                         * We must clean the toast hash before processing a
                         * completely new tuple to avoid confusion about the
                         * previous tuple's toast chunks.
                         */
                        Assert(change->data.tp.clear_toast_afterwards);
                        ReorderBufferToastReset(rb, txn);
 
                        /* We don't need this record anymore. */
                        ReorderBufferReturnChange(rb, specinsert, true);
                        specinsert = NULL;
                    }
                    break;
 
                case REORDER_BUFFER_CHANGE_TRUNCATE:
                    {
                        int         i;
                        int         nrelids = change->data.truncate.nrelids;
                        int         nrelations = 0;
                        Relation   *relations;
 
                        relations = palloc0(nrelids * sizeof(Relation));
                        for (i = 0; i < nrelids; i++)
                        {
                            Oid         relid = change->data.truncate.relids[i];
                            Relation    rel;
 
                            rel = RelationIdGetRelation(relid);
 
                            if (!RelationIsValid(rel))
                                elog(ERROR, "could not open relation with OID %u", relid);
 
                            if (!RelationIsLogicallyLogged(rel))
                                continue;
 
                            relations[nrelations++] = rel;
                        }
 
                        /* Apply the truncate. */
                        ReorderBufferApplyTruncate(rb, txn, nrelations,
                                                   relations, change,
                                                   streaming);
 
                        for (i = 0; i < nrelations; i++)
                            RelationClose(relations[i]);
 
                        break;
                    }
 
                case REORDER_BUFFER_CHANGE_MESSAGE:
                    ReorderBufferApplyMessage(rb, txn, change, streaming);
                    break;
 
                case REORDER_BUFFER_CHANGE_INVALIDATION:
                    /* Execute the invalidation messages locally */
                    ReorderBufferExecuteInvalidations(change->data.inval.ninvalidations,
                                                      change->data.inval.invalidations);
                    break;
 
                case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
                    /* get rid of the old */
                    TeardownHistoricSnapshot(false);
 
                    if (snapshot_now->copied)
                    {
                        ReorderBufferFreeSnap(rb, snapshot_now);
                        snapshot_now =
                            ReorderBufferCopySnap(rb, change->data.snapshot,
                                                  txn, command_id);
                    }
 
                    /*
                     * Restored from disk, need to be careful not to double
                     * free. We could introduce refcounting for that, but for
                     * now this seems infrequent enough not to care.
                     */
                    else if (change->data.snapshot->copied)
                    {
                        snapshot_now =
                            ReorderBufferCopySnap(rb, change->data.snapshot,
                                                  txn, command_id);
                    }
                    else
                    {
                        snapshot_now = change->data.snapshot;
                    }
 
                    /* and continue with the new one */
                    SetupHistoricSnapshot(snapshot_now, txn->tuplecid_hash);
                    break;
 
                case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
                    Assert(change->data.command_id != InvalidCommandId);
 
                    if (command_id < change->data.command_id)
                    {
                        command_id = change->data.command_id;
 
                        if (!snapshot_now->copied)
                        {
                            /* we don't use the global one anymore */
                            snapshot_now = ReorderBufferCopySnap(rb, snapshot_now,
                                                                 txn, command_id);
                        }
 
                        snapshot_now->curcid = command_id;
 
                        TeardownHistoricSnapshot(false);
                        SetupHistoricSnapshot(snapshot_now, txn->tuplecid_hash);
                    }
 
                    break;
 
                case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
                    elog(ERROR, "tuplecid value in changequeue");
                    break;
            }
 
            /*
             * It is possible that the data is not sent to downstream for a
             * long time either because the output plugin filtered it or there
             * is a DDL that generates a lot of data that is not processed by
             * the plugin. So, in such cases, the downstream can timeout. To
             * avoid that we try to send a keepalive message if required.
             * Trying to send a keepalive message after every change has some
             * overhead, but testing showed there is no noticeable overhead if
             * we do it after every ~100 changes.
             */
#define CHANGES_THRESHOLD 100
 
            if (++changes_count >= CHANGES_THRESHOLD)
            {
                rb->update_progress_txn(rb, txn, change->lsn);
                changes_count = 0;
            }
        }
 
        /* speculative insertion record must be freed by now */
        Assert(!specinsert);
 
        /* clean up the iterator */
        ReorderBufferIterTXNFinish(rb, iterstate);
        iterstate = NULL;
 
        /*
         * Update total transaction count and total bytes processed by the
         * transaction and its subtransactions. Ensure to not count the
         * streamed transaction multiple times.
         *
         * Note that the statistics computation has to be done after
         * ReorderBufferIterTXNFinish as it releases the serialized change
         * which we have already accounted in ReorderBufferIterTXNNext.
         */
        if (!rbtxn_is_streamed(txn))
            rb->totalTxns++;
 
        rb->totalBytes += txn->total_size;
 
        /*
         * Done with current changes, send the last message for this set of
         * changes depending upon streaming mode.
         */
        if (streaming)
        {
            if (stream_started)
            {
                rb->stream_stop(rb, txn, prev_lsn);
                stream_started = false;
            }
        }
        else
        {
            /*
             * Call either PREPARE (for two-phase transactions) or COMMIT (for
             * regular ones).
             */
            if (rbtxn_prepared(txn))
                rb->prepare(rb, txn, commit_lsn);
            else
                rb->commit(rb, txn, commit_lsn);
        }
 
        /* this is just a sanity check against bad output plugin behaviour */
        if (GetCurrentTransactionIdIfAny() != InvalidTransactionId)
            elog(ERROR, "output plugin used XID %u",
                 GetCurrentTransactionId());
 
        /*
         * Remember the command ID and snapshot for the next set of changes in
         * streaming mode.
         */
        if (streaming)
            ReorderBufferSaveTXNSnapshot(rb, txn, snapshot_now, command_id);
        else if (snapshot_now->copied)
            ReorderBufferFreeSnap(rb, snapshot_now);
 
        /* cleanup */
        TeardownHistoricSnapshot(false);
 
        /*
         * Aborting the current (sub-)transaction as a whole has the right
         * semantics. We want all locks acquired in here to be released, not
         * reassigned to the parent and we do not want any database access
         * have persistent effects.
         */
        AbortCurrentTransaction();
 
        /* make sure there's no cache pollution */
        ReorderBufferExecuteInvalidations(txn->ninvalidations, txn->invalidations);
 
        if (using_subtxn)
            RollbackAndReleaseCurrentSubTransaction();
 
        /*
         * We are here due to one of the four reasons: 1. Decoding an
         * in-progress txn. 2. Decoding a prepared txn. 3. Decoding of a
         * prepared txn that was (partially) streamed. 4. Decoding a committed
         * txn.
         *
         * For 1, we allow truncation of txn data by removing the changes
         * already streamed but still keeping other things like invalidations,
         * snapshot, and tuplecids. For 2 and 3, we indicate
         * ReorderBufferTruncateTXN to do more elaborate truncation of txn
         * data as the entire transaction has been decoded except for commit.
         * For 4, as the entire txn has been decoded, we can fully clean up
         * the TXN reorder buffer.
         */
        if (streaming || rbtxn_prepared(txn))
        {
            ReorderBufferTruncateTXN(rb, txn, rbtxn_prepared(txn));
            /* Reset the CheckXidAlive */
            CheckXidAlive = InvalidTransactionId;
        }
        else
            ReorderBufferCleanupTXN(rb, txn);
    }
    PG_CATCH();
    {
        MemoryContext ecxt = MemoryContextSwitchTo(ccxt);
        ErrorData  *errdata = CopyErrorData();
 
        /* TODO: Encapsulate cleanup from the PG_TRY and PG_CATCH blocks */
        if (iterstate)
            ReorderBufferIterTXNFinish(rb, iterstate);
 
        TeardownHistoricSnapshot(true);
 
        /*
         * Force cache invalidation to happen outside of a valid transaction
         * to prevent catalog access as we just caught an error.
         */
        AbortCurrentTransaction();
 
        /* make sure there's no cache pollution */
        ReorderBufferExecuteInvalidations(txn->ninvalidations,
                                          txn->invalidations);
 
        if (using_subtxn)
            RollbackAndReleaseCurrentSubTransaction();
 
        /*
         * The error code ERRCODE_TRANSACTION_ROLLBACK indicates a concurrent
         * abort of the (sub)transaction we are streaming or preparing. We
         * need to do the cleanup and return gracefully on this error, see
         * SetupCheckXidLive.
         *
         * This error code can be thrown by one of the callbacks we call
         * during decoding so we need to ensure that we return gracefully only
         * when we are sending the data in streaming mode and the streaming is
         * not finished yet or when we are sending the data out on a PREPARE
         * during a two-phase commit.
         */
        if (errdata->sqlerrcode == ERRCODE_TRANSACTION_ROLLBACK &&
            (stream_started || rbtxn_prepared(txn)))
        {
            /* curtxn must be set for streaming or prepared transactions */
            Assert(curtxn);
 
            /* Cleanup the temporary error state. */
            FlushErrorState();
            FreeErrorData(errdata);
            errdata = NULL;
            curtxn->concurrent_abort = true;
 
            /* Reset the TXN so that it is allowed to stream remaining data. */
            ReorderBufferResetTXN(rb, txn, snapshot_now,
                                  command_id, prev_lsn,
                                  specinsert);
        }
        else
        {
            ReorderBufferCleanupTXN(rb, txn);
            MemoryContextSwitchTo(ecxt);
            PG_RE_THROW();
        }
    }
    PG_END_TRY();
}
 
/*
 * Perform the replay of a transaction and its non-aborted subtransactions.
 *
 * Subtransactions previously have to be processed by
 * ReorderBufferCommitChild(), even if previously assigned to the toplevel
 * transaction with ReorderBufferAssignChild.
 *
 * This interface is called once a prepare or toplevel commit is read for both
 * streamed as well as non-streamed transactions.
 */
static void
ReorderBufferReplay(ReorderBufferTXN *txn,
                    ReorderBuffer *rb, TransactionId xid,
                    XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
                    TimestampTz commit_time,
                    RepOriginId origin_id, XLogRecPtr origin_lsn)
{
    Snapshot    snapshot_now;
    CommandId   command_id = FirstCommandId;
 
    txn->final_lsn = commit_lsn;
    txn->end_lsn = end_lsn;
    txn->xact_time.commit_time = commit_time;
    txn->origin_id = origin_id;
    txn->origin_lsn = origin_lsn;
 
    /*
     * If the transaction was (partially) streamed, we need to commit it in a
     * 'streamed' way. That is, we first stream the remaining part of the
     * transaction, and then invoke stream_commit message.
     *
     * Called after everything (origin ID, LSN, ...) is stored in the
     * transaction to avoid passing that information directly.
     */
    if (rbtxn_is_streamed(txn))
    {
        ReorderBufferStreamCommit(rb, txn);
        return;
    }
 
    /*
     * If this transaction has no snapshot, it didn't make any changes to the
     * database, so there's nothing to decode.  Note that
     * ReorderBufferCommitChild will have transferred any snapshots from
     * subtransactions if there were any.
     */
    if (txn->base_snapshot == NULL)
    {
        Assert(txn->ninvalidations == 0);
 
        /*
         * Removing this txn before a commit might result in the computation
         * of an incorrect restart_lsn. See SnapBuildProcessRunningXacts.
         */
        if (!rbtxn_prepared(txn))
            ReorderBufferCleanupTXN(rb, txn);
        return;
    }
 
    snapshot_now = txn->base_snapshot;
 
    /* Process and send the changes to output plugin. */
    ReorderBufferProcessTXN(rb, txn, commit_lsn, snapshot_now,
                            command_id, false);
}
 
/*
 * Commit a transaction.
 *
 * See comments for ReorderBufferReplay().
 */
void
ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
                    XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
                    TimestampTz commit_time,
                    RepOriginId origin_id, XLogRecPtr origin_lsn)
{
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
                                false);
 
    /* unknown transaction, nothing to replay */
    if (txn == NULL)
        return;
 
    ReorderBufferReplay(txn, rb, xid, commit_lsn, end_lsn, commit_time,
                        origin_id, origin_lsn);
}
 
/*
 * Record the prepare information for a transaction.
 */
bool
ReorderBufferRememberPrepareInfo(ReorderBuffer *rb, TransactionId xid,
                                 XLogRecPtr prepare_lsn, XLogRecPtr end_lsn,
                                 TimestampTz prepare_time,
                                 RepOriginId origin_id, XLogRecPtr origin_lsn)
{
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr, false);
 
    /* unknown transaction, nothing to do */
    if (txn == NULL)
        return false;
 
    /*
     * Remember the prepare information to be later used by commit prepared in
     * case we skip doing prepare.
     */
    txn->final_lsn = prepare_lsn;
    txn->end_lsn = end_lsn;
    txn->xact_time.prepare_time = prepare_time;
    txn->origin_id = origin_id;
    txn->origin_lsn = origin_lsn;
 
    return true;
}
 
/* Remember that we have skipped prepare */
void
ReorderBufferSkipPrepare(ReorderBuffer *rb, TransactionId xid)
{
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr, false);
 
    /* unknown transaction, nothing to do */
    if (txn == NULL)
        return;
 
    txn->txn_flags |= RBTXN_SKIPPED_PREPARE;
}
 
/*
 * Prepare a two-phase transaction.
 *
 * See comments for ReorderBufferReplay().
 */
void
ReorderBufferPrepare(ReorderBuffer *rb, TransactionId xid,
                     char *gid)
{
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
                                false);
 
    /* unknown transaction, nothing to replay */
    if (txn == NULL)
        return;
 
    txn->txn_flags |= RBTXN_PREPARE;
    txn->gid = pstrdup(gid);
 
    /* The prepare info must have been updated in txn by now. */
    Assert(txn->final_lsn != InvalidXLogRecPtr);
 
    ReorderBufferReplay(txn, rb, xid, txn->final_lsn, txn->end_lsn,
                        txn->xact_time.prepare_time, txn->origin_id, txn->origin_lsn);
 
    /*
     * We send the prepare for the concurrently aborted xacts so that later
     * when rollback prepared is decoded and sent, the downstream should be
     * able to rollback such a xact. See comments atop DecodePrepare.
     *
     * Note, for the concurrent_abort + streaming case a stream_prepare was
     * already sent within the ReorderBufferReplay call above.
     */
    if (txn->concurrent_abort && !rbtxn_is_streamed(txn))
        rb->prepare(rb, txn, txn->final_lsn);
}
 
/*
 * This is used to handle COMMIT/ROLLBACK PREPARED.
 */
void
ReorderBufferFinishPrepared(ReorderBuffer *rb, TransactionId xid,
                            XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
                            XLogRecPtr two_phase_at,
                            TimestampTz commit_time, RepOriginId origin_id,
                            XLogRecPtr origin_lsn, char *gid, bool is_commit)
{
    ReorderBufferTXN *txn;
    XLogRecPtr  prepare_end_lsn;
    TimestampTz prepare_time;
 
    txn = ReorderBufferTXNByXid(rb, xid, false, NULL, commit_lsn, false);
 
    /* unknown transaction, nothing to do */
    if (txn == NULL)
        return;
 
    /*
     * By this time the txn has the prepare record information, remember it to
     * be later used for rollback.
     */
    prepare_end_lsn = txn->end_lsn;
    prepare_time = txn->xact_time.prepare_time;
 
    /* add the gid in the txn */
    txn->gid = pstrdup(gid);
 
    /*
     * It is possible that this transaction is not decoded at prepare time
     * either because by that time we didn't have a consistent snapshot, or
     * two_phase was not enabled, or it was decoded earlier but we have
     * restarted. We only need to send the prepare if it was not decoded
     * earlier. We don't need to decode the xact for aborts if it is not done
     * already.
     */
    if ((txn->final_lsn < two_phase_at) && is_commit)
    {
        txn->txn_flags |= RBTXN_PREPARE;
 
        /*
         * The prepare info must have been updated in txn even if we skip
         * prepare.
         */
        Assert(txn->final_lsn != InvalidXLogRecPtr);
 
        /*
         * By this time the txn has the prepare record information and it is
         * important to use that so that downstream gets the accurate
         * information. If instead, we have passed commit information here
         * then downstream can behave as it has already replayed commit
         * prepared after the restart.
         */
        ReorderBufferReplay(txn, rb, xid, txn->final_lsn, txn->end_lsn,
                            txn->xact_time.prepare_time, txn->origin_id, txn->origin_lsn);
    }
 
    txn->final_lsn = commit_lsn;
    txn->end_lsn = end_lsn;
    txn->xact_time.commit_time = commit_time;
    txn->origin_id = origin_id;
    txn->origin_lsn = origin_lsn;
 
    if (is_commit)
        rb->commit_prepared(rb, txn, commit_lsn);
    else
        rb->rollback_prepared(rb, txn, prepare_end_lsn, prepare_time);
 
    /* cleanup: make sure there's no cache pollution */
    ReorderBufferExecuteInvalidations(txn->ninvalidations,
                                      txn->invalidations);
    ReorderBufferCleanupTXN(rb, txn);
}
 
/*
 * Abort a transaction that possibly has previous changes. Needs to be first
 * called for subtransactions and then for the toplevel xid.
 *
 * NB: Transactions handled here have to have actively aborted (i.e. have
 * produced an abort record). Implicitly aborted transactions are handled via
 * ReorderBufferAbortOld(); transactions we're just not interested in, but
 * which have committed are handled in ReorderBufferForget().
 *
 * This function purges this transaction and its contents from memory and
 * disk.
 */
void
ReorderBufferAbort(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
                   TimestampTz abort_time)
{
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
                                false);
 
    /* unknown, nothing to remove */
    if (txn == NULL)
        return;
 
    txn->xact_time.abort_time = abort_time;
 
    /* For streamed transactions notify the remote node about the abort. */
    if (rbtxn_is_streamed(txn))
    {
        rb->stream_abort(rb, txn, lsn);
 
        /*
         * We might have decoded changes for this transaction that could load
         * the cache as per the current transaction's view (consider DDL's
         * happened in this transaction). We don't want the decoding of future
         * transactions to use those cache entries so execute invalidations.
         */
        if (txn->ninvalidations > 0)
            ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
                                               txn->invalidations);
    }
 
    /* cosmetic... */
    txn->final_lsn = lsn;
 
    /* remove potential on-disk data, and deallocate */
    ReorderBufferCleanupTXN(rb, txn);
}
 
/*
 * Abort all transactions that aren't actually running anymore because the
 * server restarted.
 *
 * NB: These really have to be transactions that have aborted due to a server
 * crash/immediate restart, as we don't deal with invalidations here.
 */
void
ReorderBufferAbortOld(ReorderBuffer *rb, TransactionId oldestRunningXid)
{
    dlist_mutable_iter it;
 
    /*
     * Iterate through all (potential) toplevel TXNs and abort all that are
     * older than what possibly can be running. Once we've found the first
     * that is alive we stop, there might be some that acquired an xid earlier
     * but started writing later, but it's unlikely and they will be cleaned
     * up in a later call to this function.
     */
    dlist_foreach_modify(it, &rb->toplevel_by_lsn)
    {
        ReorderBufferTXN *txn;
 
        txn = dlist_container(ReorderBufferTXN, node, it.cur);
 
        if (TransactionIdPrecedes(txn->xid, oldestRunningXid))
        {
            elog(DEBUG2, "aborting old transaction %u", txn->xid);
 
            /* Notify the remote node about the crash/immediate restart. */
            if (rbtxn_is_streamed(txn))
                rb->stream_abort(rb, txn, InvalidXLogRecPtr);
 
            /* remove potential on-disk data, and deallocate this tx */
            ReorderBufferCleanupTXN(rb, txn);
        }
        else
            return;
    }
}
 
/*
 * Forget the contents of a transaction if we aren't interested in its
 * contents. Needs to be first called for subtransactions and then for the
 * toplevel xid.
 *
 * This is significantly different to ReorderBufferAbort() because
 * transactions that have committed need to be treated differently from aborted
 * ones since they may have modified the catalog.
 *
 * Note that this is only allowed to be called in the moment a transaction
 * commit has just been read, not earlier; otherwise later records referring
 * to this xid might re-create the transaction incompletely.
 */
void
ReorderBufferForget(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
{
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
                                false);
 
    /* unknown, nothing to forget */
    if (txn == NULL)
        return;
 
    /* this transaction mustn't be streamed */
    Assert(!rbtxn_is_streamed(txn));
 
    /* cosmetic... */
    txn->final_lsn = lsn;
 
    /*
     * Process cache invalidation messages if there are any. Even if we're not
     * interested in the transaction's contents, it could have manipulated the
     * catalog and we need to update the caches according to that.
     */
    if (txn->base_snapshot != NULL && txn->ninvalidations > 0)
        ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
                                           txn->invalidations);
    else
        Assert(txn->ninvalidations == 0);
 
    /* remove potential on-disk data, and deallocate */
    ReorderBufferCleanupTXN(rb, txn);
}
 
/*
 * Invalidate cache for those transactions that need to be skipped just in case
 * catalogs were manipulated as part of the transaction.
 *
 * Note that this is a special-purpose function for prepared transactions where
 * we don't want to clean up the TXN even when we decide to skip it. See
 * DecodePrepare.
 */
void
ReorderBufferInvalidate(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
{
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
                                false);
 
    /* unknown, nothing to do */
    if (txn == NULL)
        return;
 
    /*
     * Process cache invalidation messages if there are any. Even if we're not
     * interested in the transaction's contents, it could have manipulated the
     * catalog and we need to update the caches according to that.
     */
    if (txn->base_snapshot != NULL && txn->ninvalidations > 0)
        ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
                                           txn->invalidations);
    else
        Assert(txn->ninvalidations == 0);
}
 
 
/*
 * Execute invalidations happening outside the context of a decoded
 * transaction. That currently happens either for xid-less commits
 * (cf. RecordTransactionCommit()) or for invalidations in uninteresting
 * transactions (via ReorderBufferForget()).
 */
void
ReorderBufferImmediateInvalidation(ReorderBuffer *rb, uint32 ninvalidations,
                                   SharedInvalidationMessage *invalidations)
{
    bool        use_subtxn = IsTransactionOrTransactionBlock();
    int         i;
 
    if (use_subtxn)
        BeginInternalSubTransaction("replay");
 
    /*
     * Force invalidations to happen outside of a valid transaction - that way
     * entries will just be marked as invalid without accessing the catalog.
     * That's advantageous because we don't need to setup the full state
     * necessary for catalog access.
     */
    if (use_subtxn)
        AbortCurrentTransaction();
 
    for (i = 0; i < ninvalidations; i++)
        LocalExecuteInvalidationMessage(&invalidations[i]);
 
    if (use_subtxn)
        RollbackAndReleaseCurrentSubTransaction();
}
 
/*
 * Tell reorderbuffer about an xid seen in the WAL stream. Has to be called at
 * least once for every xid in XLogRecord->xl_xid (other places in records
 * may, but do not have to be passed through here).
 *
 * Reorderbuffer keeps some data structures about transactions in LSN order,
 * for efficiency. To do that it has to know about when transactions are seen
 * first in the WAL. As many types of records are not actually interesting for
 * logical decoding, they do not necessarily pass through here.
 */
void
ReorderBufferProcessXid(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
{
    /* many records won't have an xid assigned, centralize check here */
    if (xid != InvalidTransactionId)
        ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
}
 
/*
 * Add a new snapshot to this transaction that may only used after lsn 'lsn'
 * because the previous snapshot doesn't describe the catalog correctly for
 * following rows.
 */
void
ReorderBufferAddSnapshot(ReorderBuffer *rb, TransactionId xid,
                         XLogRecPtr lsn, Snapshot snap)
{
    ReorderBufferChange *change = ReorderBufferGetChange(rb);
 
    change->data.snapshot = snap;
    change->action = REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT;
 
    ReorderBufferQueueChange(rb, xid, lsn, change, false);
}
 
/*
 * Set up the transaction's base snapshot.
 *
 * If we know that xid is a subtransaction, set the base snapshot on the
 * top-level transaction instead.
 */
void
ReorderBufferSetBaseSnapshot(ReorderBuffer *rb, TransactionId xid,
                             XLogRecPtr lsn, Snapshot snap)
{
    ReorderBufferTXN *txn;
    bool        is_new;
 
    Assert(snap != NULL);
 
    /*
     * Fetch the transaction to operate on.  If we know it's a subtransaction,
     * operate on its top-level transaction instead.
     */
    txn = ReorderBufferTXNByXid(rb, xid, true, &is_new, lsn, true);
    if (rbtxn_is_known_subxact(txn))
        txn = ReorderBufferTXNByXid(rb, txn->toplevel_xid, false,
                                    NULL, InvalidXLogRecPtr, false);
    Assert(txn->base_snapshot == NULL);
 
    txn->base_snapshot = snap;
    txn->base_snapshot_lsn = lsn;
    dlist_push_tail(&rb->txns_by_base_snapshot_lsn, &txn->base_snapshot_node);
 
    AssertTXNLsnOrder(rb);
}
 
/*
 * Access the catalog with this CommandId at this point in the changestream.
 *
 * May only be called for command ids > 1
 */
void
ReorderBufferAddNewCommandId(ReorderBuffer *rb, TransactionId xid,
                             XLogRecPtr lsn, CommandId cid)
{
    ReorderBufferChange *change = ReorderBufferGetChange(rb);
 
    change->data.command_id = cid;
    change->action = REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID;
 
    ReorderBufferQueueChange(rb, xid, lsn, change, false);
}
 
/*
 * Update memory counters to account for the new or removed change.
 *
 * We update two counters - in the reorder buffer, and in the transaction
 * containing the change. The reorder buffer counter allows us to quickly
 * decide if we reached the memory limit, the transaction counter allows
 * us to quickly pick the largest transaction for eviction.
 *
 * Either txn or change must be non-NULL at least. We update the memory
 * counter of txn if it's non-NULL, otherwise change->txn.
 *
 * When streaming is enabled, we need to update the toplevel transaction
 * counters instead - we don't really care about subtransactions as we
 * can't stream them individually anyway, and we only pick toplevel
 * transactions for eviction. So only toplevel transactions matter.
 */
static void
ReorderBufferChangeMemoryUpdate(ReorderBuffer *rb,
                                ReorderBufferChange *change,
                                ReorderBufferTXN *txn,
                                bool addition, Size sz)
{
    ReorderBufferTXN *toptxn;
 
    Assert(txn || change);
 
    /*
     * Ignore tuple CID changes, because those are not evicted when reaching
     * memory limit. So we just don't count them, because it might easily
     * trigger a pointless attempt to spill.
     */
    if (change && change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID)
        return;
 
    if (sz == 0)
        return;
 
    if (txn == NULL)
        txn = change->txn;
    Assert(txn != NULL);
 
    /*
     * Update the total size in top level as well. This is later used to
     * compute the decoding stats.
     */
    toptxn = rbtxn_get_toptxn(txn);
 
    if (addition)
    {
        Size        oldsize = txn->size;
 
        txn->size += sz;
        rb->size += sz;
 
        /* Update the total size in the top transaction. */
        toptxn->total_size += sz;
 
        /* Update the max-heap */
        if (oldsize != 0)
            pairingheap_remove(rb->txn_heap, &txn->txn_node);
        pairingheap_add(rb->txn_heap, &txn->txn_node);
    }
    else
    {
        Assert((rb->size >= sz) && (txn->size >= sz));
        txn->size -= sz;
        rb->size -= sz;
 
        /* Update the total size in the top transaction. */
        toptxn->total_size -= sz;
 
        /* Update the max-heap */
        pairingheap_remove(rb->txn_heap, &txn->txn_node);
        if (txn->size != 0)
            pairingheap_add(rb->txn_heap, &txn->txn_node);
    }
 
    Assert(txn->size <= rb->size);
}
 
/*
 * Add new (relfilelocator, tid) -> (cmin, cmax) mappings.
 *
 * We do not include this change type in memory accounting, because we
 * keep CIDs in a separate list and do not evict them when reaching
 * the memory limit.
 */
void
ReorderBufferAddNewTupleCids(ReorderBuffer *rb, TransactionId xid,
                             XLogRecPtr lsn, RelFileLocator locator,
                             ItemPointerData tid, CommandId cmin,
                             CommandId cmax, CommandId combocid)
{
    ReorderBufferChange *change = ReorderBufferGetChange(rb);
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
 
    change->data.tuplecid.locator = locator;
    change->data.tuplecid.tid = tid;
    change->data.tuplecid.cmin = cmin;
    change->data.tuplecid.cmax = cmax;
    change->data.tuplecid.combocid = combocid;
    change->lsn = lsn;
    change->txn = txn;
    change->action = REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID;
 
    dlist_push_tail(&txn->tuplecids, &change->node);
    txn->ntuplecids++;
}
 
/*
 * Accumulate the invalidations for executing them later.
 *
 * This needs to be called for each XLOG_XACT_INVALIDATIONS message and
 * accumulates all the invalidation messages in the toplevel transaction, if
 * available, otherwise in the current transaction, as well as in the form of
 * change in reorder buffer.  We require to record it in form of the change
 * so that we can execute only the required invalidations instead of executing
 * all the invalidations on each CommandId increment.  We also need to
 * accumulate these in the txn buffer because in some cases where we skip
 * processing the transaction (see ReorderBufferForget), we need to execute
 * all the invalidations together.
 */
void
ReorderBufferAddInvalidations(ReorderBuffer *rb, TransactionId xid,
                              XLogRecPtr lsn, Size nmsgs,
                              SharedInvalidationMessage *msgs)
{
    ReorderBufferTXN *txn;
    MemoryContext oldcontext;
    ReorderBufferChange *change;
 
    txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
 
    oldcontext = MemoryContextSwitchTo(rb->context);
 
    /*
     * Collect all the invalidations under the top transaction, if available,
     * so that we can execute them all together.  See comments atop this
     * function.
     */
    txn = rbtxn_get_toptxn(txn);
 
    Assert(nmsgs > 0);
 
    /* Accumulate invalidations. */
    if (txn->ninvalidations == 0)
    {
        txn->ninvalidations = nmsgs;
        txn->invalidations = (SharedInvalidationMessage *)
            palloc(sizeof(SharedInvalidationMessage) * nmsgs);
        memcpy(txn->invalidations, msgs,
               sizeof(SharedInvalidationMessage) * nmsgs);
    }
    else
    {
        txn->invalidations = (SharedInvalidationMessage *)
            repalloc(txn->invalidations, sizeof(SharedInvalidationMessage) *
                     (txn->ninvalidations + nmsgs));
 
        memcpy(txn->invalidations + txn->ninvalidations, msgs,
               nmsgs * sizeof(SharedInvalidationMessage));
        txn->ninvalidations += nmsgs;
    }
 
    change = ReorderBufferGetChange(rb);
    change->action = REORDER_BUFFER_CHANGE_INVALIDATION;
    change->data.inval.ninvalidations = nmsgs;
    change->data.inval.invalidations = (SharedInvalidationMessage *)
        palloc(sizeof(SharedInvalidationMessage) * nmsgs);
    memcpy(change->data.inval.invalidations, msgs,
           sizeof(SharedInvalidationMessage) * nmsgs);
 
    ReorderBufferQueueChange(rb, xid, lsn, change, false);
 
    MemoryContextSwitchTo(oldcontext);
}
 
/*
 * Apply all invalidations we know. Possibly we only need parts at this point
 * in the changestream but we don't know which those are.
 */
static void
ReorderBufferExecuteInvalidations(uint32 nmsgs, SharedInvalidationMessage *msgs)
{
    int         i;
 
    for (i = 0; i < nmsgs; i++)
        LocalExecuteInvalidationMessage(&msgs[i]);
}
 
/*
 * Mark a transaction as containing catalog changes
 */
void
ReorderBufferXidSetCatalogChanges(ReorderBuffer *rb, TransactionId xid,
                                  XLogRecPtr lsn)
{
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
 
    if (!rbtxn_has_catalog_changes(txn))
    {
        txn->txn_flags |= RBTXN_HAS_CATALOG_CHANGES;
        dclist_push_tail(&rb->catchange_txns, &txn->catchange_node);
    }
 
    /*
     * Mark top-level transaction as having catalog changes too if one of its
     * children has so that the ReorderBufferBuildTupleCidHash can
     * conveniently check just top-level transaction and decide whether to
     * build the hash table or not.
     */
    if (rbtxn_is_subtxn(txn))
    {
        ReorderBufferTXN *toptxn = rbtxn_get_toptxn(txn);
 
        if (!rbtxn_has_catalog_changes(toptxn))
        {
            toptxn->txn_flags |= RBTXN_HAS_CATALOG_CHANGES;
            dclist_push_tail(&rb->catchange_txns, &toptxn->catchange_node);
        }
    }
}
 
/*
 * Return palloc'ed array of the transactions that have changed catalogs.
 * The returned array is sorted in xidComparator order.
 *
 * The caller must free the returned array when done with it.
 */
TransactionId *
ReorderBufferGetCatalogChangesXacts(ReorderBuffer *rb)
{
    dlist_iter  iter;
    TransactionId *xids = NULL;
    size_t      xcnt = 0;
 
    /* Quick return if the list is empty */
    if (dclist_count(&rb->catchange_txns) == 0)
        return NULL;
 
    /* Initialize XID array */
    xids = (TransactionId *) palloc(sizeof(TransactionId) *
                                    dclist_count(&rb->catchange_txns));
    dclist_foreach(iter, &rb->catchange_txns)
    {
        ReorderBufferTXN *txn = dclist_container(ReorderBufferTXN,
                                                 catchange_node,
                                                 iter.cur);
 
        Assert(rbtxn_has_catalog_changes(txn));
 
        xids[xcnt++] = txn->xid;
    }
 
    qsort(xids, xcnt, sizeof(TransactionId), xidComparator);
 
    Assert(xcnt == dclist_count(&rb->catchange_txns));
    return xids;
}
 
/*
 * Query whether a transaction is already *known* to contain catalog
 * changes. This can be wrong until directly before the commit!
 */
bool
ReorderBufferXidHasCatalogChanges(ReorderBuffer *rb, TransactionId xid)
{
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
                                false);
    if (txn == NULL)
        return false;
 
    return rbtxn_has_catalog_changes(txn);
}
 
/*
 * ReorderBufferXidHasBaseSnapshot
 *      Have we already set the base snapshot for the given txn/subtxn?
 */
bool
ReorderBufferXidHasBaseSnapshot(ReorderBuffer *rb, TransactionId xid)
{
    ReorderBufferTXN *txn;
 
    txn = ReorderBufferTXNByXid(rb, xid, false,
                                NULL, InvalidXLogRecPtr, false);
 
    /* transaction isn't known yet, ergo no snapshot */
    if (txn == NULL)
        return false;
 
    /* a known subtxn? operate on top-level txn instead */
    if (rbtxn_is_known_subxact(txn))
        txn = ReorderBufferTXNByXid(rb, txn->toplevel_xid, false,
                                    NULL, InvalidXLogRecPtr, false);
 
    return txn->base_snapshot != NULL;
}
 
 
/*
 * ---------------------------------------
 * Disk serialization support
 * ---------------------------------------
 */
 
/*
 * Ensure the IO buffer is >= sz.
 */
static void
ReorderBufferSerializeReserve(ReorderBuffer *rb, Size sz)
{
    if (!rb->outbufsize)
    {
        rb->outbuf = MemoryContextAlloc(rb->context, sz);
        rb->outbufsize = sz;
    }
    else if (rb->outbufsize < sz)
    {
        rb->outbuf = repalloc(rb->outbuf, sz);
        rb->outbufsize = sz;
    }
}
 
 
/* Compare two transactions by size */
static int
ReorderBufferTXNSizeCompare(const pairingheap_node *a, const pairingheap_node *b, void *arg)
{
    const ReorderBufferTXN *ta = pairingheap_const_container(ReorderBufferTXN, txn_node, a);
    const ReorderBufferTXN *tb = pairingheap_const_container(ReorderBufferTXN, txn_node, b);
 
    if (ta->size < tb->size)
        return -1;
    if (ta->size > tb->size)
        return 1;
    return 0;
}
 
/*
 * Find the largest transaction (toplevel or subxact) to evict (spill to disk).
 */
static ReorderBufferTXN *
ReorderBufferLargestTXN(ReorderBuffer *rb)
{
    ReorderBufferTXN *largest;
 
    /* Get the largest transaction from the max-heap */
    largest = pairingheap_container(ReorderBufferTXN, txn_node,
                                    pairingheap_first(rb->txn_heap));
 
    Assert(largest);
    Assert(largest->size > 0);
    Assert(largest->size <= rb->size);
 
    return largest;
}
 
/*
 * Find the largest streamable toplevel transaction to evict (by streaming).
 *
 * This can be seen as an optimized version of ReorderBufferLargestTXN, which
 * should give us the same transaction (because we don't update memory account
 * for subtransaction with streaming, so it's always 0). But we can simply
 * iterate over the limited number of toplevel transactions that have a base
 * snapshot. There is no use of selecting a transaction that doesn't have base
 * snapshot because we don't decode such transactions.  Also, we do not select
 * the transaction which doesn't have any streamable change.
 *
 * Note that, we skip transactions that contain incomplete changes. There
 * is a scope of optimization here such that we can select the largest
 * transaction which has incomplete changes.  But that will make the code and
 * design quite complex and that might not be worth the benefit.  If we plan to
 * stream the transactions that contain incomplete changes then we need to
 * find a way to partially stream/truncate the transaction changes in-memory
 * and build a mechanism to partially truncate the spilled files.
 * Additionally, whenever we partially stream the transaction we need to
 * maintain the last streamed lsn and next time we need to restore from that
 * segment and the offset in WAL.  As we stream the changes from the top
 * transaction and restore them subtransaction wise, we need to even remember
 * the subxact from where we streamed the last change.
 */
static ReorderBufferTXN *
ReorderBufferLargestStreamableTopTXN(ReorderBuffer *rb)
{
    dlist_iter  iter;
    Size        largest_size = 0;
    ReorderBufferTXN *largest = NULL;
 
    /* Find the largest top-level transaction having a base snapshot. */
    dlist_foreach(iter, &rb->txns_by_base_snapshot_lsn)
    {
        ReorderBufferTXN *txn;
 
        txn = dlist_container(ReorderBufferTXN, base_snapshot_node, iter.cur);
 
        /* must not be a subtxn */
        Assert(!rbtxn_is_known_subxact(txn));
        /* base_snapshot must be set */
        Assert(txn->base_snapshot != NULL);
 
        if ((largest == NULL || txn->total_size > largest_size) &&
            (txn->total_size > 0) && !(rbtxn_has_partial_change(txn)) &&
            rbtxn_has_streamable_change(txn))
        {
            largest = txn;
            largest_size = txn->total_size;
        }
    }
 
    return largest;
}
 
/*
 * Check whether the logical_decoding_work_mem limit was reached, and if yes
 * pick the largest (sub)transaction at-a-time to evict and spill its changes to
 * disk or send to the output plugin until we reach under the memory limit.
 *
 * If debug_logical_replication_streaming is set to "immediate", stream or
 * serialize the changes immediately.
 *
 * XXX At this point we select the transactions until we reach under the memory
 * limit, but we might also adapt a more elaborate eviction strategy - for example
 * evicting enough transactions to free certain fraction (e.g. 50%) of the memory
 * limit.
 */
static void
ReorderBufferCheckMemoryLimit(ReorderBuffer *rb)
{
    ReorderBufferTXN *txn;
 
    /*
     * Bail out if debug_logical_replication_streaming is buffered and we
     * haven't exceeded the memory limit.
     */
    if (debug_logical_replication_streaming == DEBUG_LOGICAL_REP_STREAMING_BUFFERED &&
        rb->size < logical_decoding_work_mem * 1024L)
        return;
 
    /*
     * If debug_logical_replication_streaming is immediate, loop until there's
     * no change. Otherwise, loop until we reach under the memory limit. One
     * might think that just by evicting the largest (sub)transaction we will
     * come under the memory limit based on assumption that the selected
     * transaction is at least as large as the most recent change (which
     * caused us to go over the memory limit). However, that is not true
     * because a user can reduce the logical_decoding_work_mem to a smaller
     * value before the most recent change.
     */
    while (rb->size >= logical_decoding_work_mem * 1024L ||
           (debug_logical_replication_streaming == DEBUG_LOGICAL_REP_STREAMING_IMMEDIATE &&
            rb->size > 0))
    {
        /*
         * Pick the largest transaction and evict it from memory by streaming,
         * if possible.  Otherwise, spill to disk.
         */
        if (ReorderBufferCanStartStreaming(rb) &&
            (txn = ReorderBufferLargestStreamableTopTXN(rb)) != NULL)
        {
            /* we know there has to be one, because the size is not zero */
            Assert(txn && rbtxn_is_toptxn(txn));
            Assert(txn->total_size > 0);
            Assert(rb->size >= txn->total_size);
 
            ReorderBufferStreamTXN(rb, txn);
        }
        else
        {
            /*
             * Pick the largest transaction (or subtransaction) and evict it
             * from memory by serializing it to disk.
             */
            txn = ReorderBufferLargestTXN(rb);
 
            /* we know there has to be one, because the size is not zero */
            Assert(txn);
            Assert(txn->size > 0);
            Assert(rb->size >= txn->size);
 
            ReorderBufferSerializeTXN(rb, txn);
        }
 
        /*
         * After eviction, the transaction should have no entries in memory,
         * and should use 0 bytes for changes.
         */
        Assert(txn->size == 0);
        Assert(txn->nentries_mem == 0);
    }
 
    /* We must be under the memory limit now. */
    Assert(rb->size < logical_decoding_work_mem * 1024L);
 
}
 
/*
 * Spill data of a large transaction (and its subtransactions) to disk.
 */
static void
ReorderBufferSerializeTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
{
    dlist_iter  subtxn_i;
    dlist_mutable_iter change_i;
    int         fd = -1;
    XLogSegNo   curOpenSegNo = 0;
    Size        spilled = 0;
    Size        size = txn->size;
 
    elog(DEBUG2, "spill %u changes in XID %u to disk",
         (uint32) txn->nentries_mem, txn->xid);
 
    /* do the same to all child TXs */
    dlist_foreach(subtxn_i, &txn->subtxns)
    {
        ReorderBufferTXN *subtxn;
 
        subtxn = dlist_container(ReorderBufferTXN, node, subtxn_i.cur);
        ReorderBufferSerializeTXN(rb, subtxn);
    }
 
    /* serialize changestream */
    dlist_foreach_modify(change_i, &txn->changes)
    {
        ReorderBufferChange *change;
 
        change = dlist_container(ReorderBufferChange, node, change_i.cur);
 
        /*
         * store in segment in which it belongs by start lsn, don't split over
         * multiple segments tho
         */
        if (fd == -1 ||
            !XLByteInSeg(change->lsn, curOpenSegNo, wal_segment_size))
        {
            char        path[MAXPGPATH];
 
            if (fd != -1)
                CloseTransientFile(fd);
 
            XLByteToSeg(change->lsn, curOpenSegNo, wal_segment_size);
 
            /*
             * No need to care about TLIs here, only used during a single run,
             * so each LSN only maps to a specific WAL record.
             */
            ReorderBufferSerializedPath(path, MyReplicationSlot, txn->xid,
                                        curOpenSegNo);
 
            /* open segment, create it if necessary */
            fd = OpenTransientFile(path,
                                   O_CREAT | O_WRONLY | O_APPEND | PG_BINARY);
 
            if (fd < 0)
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not open file \"%s\": %m", path)));
        }
 
        ReorderBufferSerializeChange(rb, txn, fd, change);
        dlist_delete(&change->node);
        ReorderBufferReturnChange(rb, change, false);
 
        spilled++;
    }
 
    /* Update the memory counter */
    ReorderBufferChangeMemoryUpdate(rb, NULL, txn, false, size);
 
    /* update the statistics iff we have spilled anything */
    if (spilled)
    {
        rb->spillCount += 1;
        rb->spillBytes += size;
 
        /* don't consider already serialized transactions */
        rb->spillTxns += (rbtxn_is_serialized(txn) || rbtxn_is_serialized_clear(txn)) ? 0 : 1;
 
        /* update the decoding stats */
        UpdateDecodingStats((LogicalDecodingContext *) rb->private_data);
    }
 
    Assert(spilled == txn->nentries_mem);
    Assert(dlist_is_empty(&txn->changes));
    txn->nentries_mem = 0;
    txn->txn_flags |= RBTXN_IS_SERIALIZED;
 
    if (fd != -1)
        CloseTransientFile(fd);
}
 
/*
 * Serialize individual change to disk.
 */
static void
ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
                             int fd, ReorderBufferChange *change)
{
    ReorderBufferDiskChange *ondisk;
    Size        sz = sizeof(ReorderBufferDiskChange);
 
    ReorderBufferSerializeReserve(rb, sz);
 
    ondisk = (ReorderBufferDiskChange *) rb->outbuf;
    memcpy(&ondisk->change, change, sizeof(ReorderBufferChange));
 
    switch (change->action)
    {
            /* fall through these, they're all similar enough */
        case REORDER_BUFFER_CHANGE_INSERT:
        case REORDER_BUFFER_CHANGE_UPDATE:
        case REORDER_BUFFER_CHANGE_DELETE:
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
            {
                char       *data;
                HeapTuple   oldtup,
                            newtup;
                Size        oldlen = 0;
                Size        newlen = 0;
 
                oldtup = change->data.tp.oldtuple;
                newtup = change->data.tp.newtuple;
 
                if (oldtup)
                {
                    sz += sizeof(HeapTupleData);
                    oldlen = oldtup->t_len;
                    sz += oldlen;
                }
 
                if (newtup)
                {
                    sz += sizeof(HeapTupleData);
                    newlen = newtup->t_len;
                    sz += newlen;
                }
 
                /* make sure we have enough space */
                ReorderBufferSerializeReserve(rb, sz);
 
                data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
                /* might have been reallocated above */
                ondisk = (ReorderBufferDiskChange *) rb->outbuf;
 
                if (oldlen)
                {
                    memcpy(data, oldtup, sizeof(HeapTupleData));
                    data += sizeof(HeapTupleData);
 
                    memcpy(data, oldtup->t_data, oldlen);
                    data += oldlen;
                }
 
                if (newlen)
                {
                    memcpy(data, newtup, sizeof(HeapTupleData));
                    data += sizeof(HeapTupleData);
 
                    memcpy(data, newtup->t_data, newlen);
                    data += newlen;
                }
                break;
            }
        case REORDER_BUFFER_CHANGE_MESSAGE:
            {
                char       *data;
                Size        prefix_size = strlen(change->data.msg.prefix) + 1;
 
                sz += prefix_size + change->data.msg.message_size +
                    sizeof(Size) + sizeof(Size);
                ReorderBufferSerializeReserve(rb, sz);
 
                data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
 
                /* might have been reallocated above */
                ondisk = (ReorderBufferDiskChange *) rb->outbuf;
 
                /* write the prefix including the size */
                memcpy(data, &prefix_size, sizeof(Size));
                data += sizeof(Size);
                memcpy(data, change->data.msg.prefix,
                       prefix_size);
                data += prefix_size;
 
                /* write the message including the size */
                memcpy(data, &change->data.msg.message_size, sizeof(Size));
                data += sizeof(Size);
                memcpy(data, change->data.msg.message,
                       change->data.msg.message_size);
                data += change->data.msg.message_size;
 
                break;
            }
        case REORDER_BUFFER_CHANGE_INVALIDATION:
            {
                char       *data;
                Size        inval_size = sizeof(SharedInvalidationMessage) *
                    change->data.inval.ninvalidations;
 
                sz += inval_size;
 
                ReorderBufferSerializeReserve(rb, sz);
                data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
 
                /* might have been reallocated above */
                ondisk = (ReorderBufferDiskChange *) rb->outbuf;
                memcpy(data, change->data.inval.invalidations, inval_size);
                data += inval_size;
 
                break;
            }
        case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
            {
                Snapshot    snap;
                char       *data;
 
                snap = change->data.snapshot;
 
                sz += sizeof(SnapshotData) +
                    sizeof(TransactionId) * snap->xcnt +
                    sizeof(TransactionId) * snap->subxcnt;
 
                /* make sure we have enough space */
                ReorderBufferSerializeReserve(rb, sz);
                data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
                /* might have been reallocated above */
                ondisk = (ReorderBufferDiskChange *) rb->outbuf;
 
                memcpy(data, snap, sizeof(SnapshotData));
                data += sizeof(SnapshotData);
 
                if (snap->xcnt)
                {
                    memcpy(data, snap->xip,
                           sizeof(TransactionId) * snap->xcnt);
                    data += sizeof(TransactionId) * snap->xcnt;
                }
 
                if (snap->subxcnt)
                {
                    memcpy(data, snap->subxip,
                           sizeof(TransactionId) * snap->subxcnt);
                    data += sizeof(TransactionId) * snap->subxcnt;
                }
                break;
            }
        case REORDER_BUFFER_CHANGE_TRUNCATE:
            {
                Size        size;
                char       *data;
 
                /* account for the OIDs of truncated relations */
                size = sizeof(Oid) * change->data.truncate.nrelids;
                sz += size;
 
                /* make sure we have enough space */
                ReorderBufferSerializeReserve(rb, sz);
 
                data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
                /* might have been reallocated above */
                ondisk = (ReorderBufferDiskChange *) rb->outbuf;
 
                memcpy(data, change->data.truncate.relids, size);
                data += size;
 
                break;
            }
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
        case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
        case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
            /* ReorderBufferChange contains everything important */
            break;
    }
 
    ondisk->size = sz;
 
    errno = 0;
    pgstat_report_wait_start(WAIT_EVENT_REORDER_BUFFER_WRITE);
    if (write(fd, rb->outbuf, ondisk->size) != ondisk->size)
    {
        int         save_errno = errno;
 
        CloseTransientFile(fd);
 
        /* if write didn't set errno, assume problem is no disk space */
        errno = save_errno ? save_errno : ENOSPC;
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not write to data file for XID %u: %m",
                        txn->xid)));
    }
    pgstat_report_wait_end();
 
    /*
     * Keep the transaction's final_lsn up to date with each change we send to
     * disk, so that ReorderBufferRestoreCleanup works correctly.  (We used to
     * only do this on commit and abort records, but that doesn't work if a
     * system crash leaves a transaction without its abort record).
     *
     * Make sure not to move it backwards.
     */
    if (txn->final_lsn < change->lsn)
        txn->final_lsn = change->lsn;
 
    Assert(ondisk->change.action == change->action);
}
 
/* Returns true, if the output plugin supports streaming, false, otherwise. */
static inline bool
ReorderBufferCanStream(ReorderBuffer *rb)
{
    LogicalDecodingContext *ctx = rb->private_data;
 
    return ctx->streaming;
}
 
/* Returns true, if the streaming can be started now, false, otherwise. */
static inline bool
ReorderBufferCanStartStreaming(ReorderBuffer *rb)
{
    LogicalDecodingContext *ctx = rb->private_data;
    SnapBuild  *builder = ctx->snapshot_builder;
 
    /* We can't start streaming unless a consistent state is reached. */
    if (SnapBuildCurrentState(builder) < SNAPBUILD_CONSISTENT)
        return false;
 
    /*
     * We can't start streaming immediately even if the streaming is enabled
     * because we previously decoded this transaction and now just are
     * restarting.
     */
    if (ReorderBufferCanStream(rb) &&
        !SnapBuildXactNeedsSkip(builder, ctx->reader->ReadRecPtr))
        return true;
 
    return false;
}
 
/*
 * Send data of a large transaction (and its subtransactions) to the
 * output plugin, but using the stream API.
 */
static void
ReorderBufferStreamTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
{
    Snapshot    snapshot_now;
    CommandId   command_id;
    Size        stream_bytes;
    bool        txn_is_streamed;
 
    /* We can never reach here for a subtransaction. */
    Assert(rbtxn_is_toptxn(txn));
 
    /*
     * We can't make any assumptions about base snapshot here, similar to what
     * ReorderBufferCommit() does. That relies on base_snapshot getting
     * transferred from subxact in ReorderBufferCommitChild(), but that was
     * not yet called as the transaction is in-progress.
     *
     * So just walk the subxacts and use the same logic here. But we only need
     * to do that once, when the transaction is streamed for the first time.
     * After that we need to reuse the snapshot from the previous run.
     *
     * Unlike DecodeCommit which adds xids of all the subtransactions in
     * snapshot's xip array via SnapBuildCommitTxn, we can't do that here but
     * we do add them to subxip array instead via ReorderBufferCopySnap. This
     * allows the catalog changes made in subtransactions decoded till now to
     * be visible.
     */
    if (txn->snapshot_now == NULL)
    {
        dlist_iter  subxact_i;
 
        /* make sure this transaction is streamed for the first time */
        Assert(!rbtxn_is_streamed(txn));
 
        /* at the beginning we should have invalid command ID */
        Assert(txn->command_id == InvalidCommandId);
 
        dlist_foreach(subxact_i, &txn->subtxns)
        {
            ReorderBufferTXN *subtxn;
 
            subtxn = dlist_container(ReorderBufferTXN, node, subxact_i.cur);
            ReorderBufferTransferSnapToParent(txn, subtxn);
        }
 
        /*
         * If this transaction has no snapshot, it didn't make any changes to
         * the database till now, so there's nothing to decode.
         */
        if (txn->base_snapshot == NULL)
        {
            Assert(txn->ninvalidations == 0);
            return;
        }
 
        command_id = FirstCommandId;
        snapshot_now = ReorderBufferCopySnap(rb, txn->base_snapshot,
                                             txn, command_id);
    }
    else
    {
        /* the transaction must have been already streamed */
        Assert(rbtxn_is_streamed(txn));
 
        /*
         * Nah, we already have snapshot from the previous streaming run. We
         * assume new subxacts can't move the LSN backwards, and so can't beat
         * the LSN condition in the previous branch (so no need to walk
         * through subxacts again). In fact, we must not do that as we may be
         * using snapshot half-way through the subxact.
         */
        command_id = txn->command_id;
 
        /*
         * We can't use txn->snapshot_now directly because after the last
         * streaming run, we might have got some new sub-transactions. So we
         * need to add them to the snapshot.
         */
        snapshot_now = ReorderBufferCopySnap(rb, txn->snapshot_now,
                                             txn, command_id);
 
        /* Free the previously copied snapshot. */
        Assert(txn->snapshot_now->copied);
        ReorderBufferFreeSnap(rb, txn->snapshot_now);
        txn->snapshot_now = NULL;
    }
 
    /*
     * Remember this information to be used later to update stats. We can't
     * update the stats here as an error while processing the changes would
     * lead to the accumulation of stats even though we haven't streamed all
     * the changes.
     */
    txn_is_streamed = rbtxn_is_streamed(txn);
    stream_bytes = txn->total_size;
 
    /* Process and send the changes to output plugin. */
    ReorderBufferProcessTXN(rb, txn, InvalidXLogRecPtr, snapshot_now,
                            command_id, true);
 
    rb->streamCount += 1;
    rb->streamBytes += stream_bytes;
 
    /* Don't consider already streamed transaction. */
    rb->streamTxns += (txn_is_streamed) ? 0 : 1;
 
    /* update the decoding stats */
    UpdateDecodingStats((LogicalDecodingContext *) rb->private_data);
 
    Assert(dlist_is_empty(&txn->changes));
    Assert(txn->nentries == 0);
    Assert(txn->nentries_mem == 0);
}
 
/*
 * Size of a change in memory.
 */
static Size
ReorderBufferChangeSize(ReorderBufferChange *change)
{
    Size        sz = sizeof(ReorderBufferChange);
 
    switch (change->action)
    {
            /* fall through these, they're all similar enough */
        case REORDER_BUFFER_CHANGE_INSERT:
        case REORDER_BUFFER_CHANGE_UPDATE:
        case REORDER_BUFFER_CHANGE_DELETE:
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
            {
                HeapTuple   oldtup,
                            newtup;
                Size        oldlen = 0;
                Size        newlen = 0;
 
                oldtup = change->data.tp.oldtuple;
                newtup = change->data.tp.newtuple;
 
                if (oldtup)
                {
                    sz += sizeof(HeapTupleData);
                    oldlen = oldtup->t_len;
                    sz += oldlen;
                }
 
                if (newtup)
                {
                    sz += sizeof(HeapTupleData);
                    newlen = newtup->t_len;
                    sz += newlen;
                }
 
                break;
            }
        case REORDER_BUFFER_CHANGE_MESSAGE:
            {
                Size        prefix_size = strlen(change->data.msg.prefix) + 1;
 
                sz += prefix_size + change->data.msg.message_size +
                    sizeof(Size) + sizeof(Size);
 
                break;
            }
        case REORDER_BUFFER_CHANGE_INVALIDATION:
            {
                sz += sizeof(SharedInvalidationMessage) *
                    change->data.inval.ninvalidations;
                break;
            }
        case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
            {
                Snapshot    snap;
 
                snap = change->data.snapshot;
 
                sz += sizeof(SnapshotData) +
                    sizeof(TransactionId) * snap->xcnt +
                    sizeof(TransactionId) * snap->subxcnt;
 
                break;
            }
        case REORDER_BUFFER_CHANGE_TRUNCATE:
            {
                sz += sizeof(Oid) * change->data.truncate.nrelids;
 
                break;
            }
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
        case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
        case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
            /* ReorderBufferChange contains everything important */
            break;
    }
 
    return sz;
}
 
 
/*
 * Restore a number of changes spilled to disk back into memory.
 */
static Size
ReorderBufferRestoreChanges(ReorderBuffer *rb, ReorderBufferTXN *txn,
                            TXNEntryFile *file, XLogSegNo *segno)
{
    Size        restored = 0;
    XLogSegNo   last_segno;
    dlist_mutable_iter cleanup_iter;
    File       *fd = &file->vfd;
 
    Assert(txn->first_lsn != InvalidXLogRecPtr);
    Assert(txn->final_lsn != InvalidXLogRecPtr);
 
    /* free current entries, so we have memory for more */
    dlist_foreach_modify(cleanup_iter, &txn->changes)
    {
        ReorderBufferChange *cleanup =
            dlist_container(ReorderBufferChange, node, cleanup_iter.cur);
 
        dlist_delete(&cleanup->node);
        ReorderBufferReturnChange(rb, cleanup, true);
    }
    txn->nentries_mem = 0;
    Assert(dlist_is_empty(&txn->changes));
 
    XLByteToSeg(txn->final_lsn, last_segno, wal_segment_size);
 
    while (restored < max_changes_in_memory && *segno <= last_segno)
    {
        int         readBytes;
        ReorderBufferDiskChange *ondisk;
 
        CHECK_FOR_INTERRUPTS();
 
        if (*fd == -1)
        {
            char        path[MAXPGPATH];
 
            /* first time in */
            if (*segno == 0)
                XLByteToSeg(txn->first_lsn, *segno, wal_segment_size);
 
            Assert(*segno != 0 || dlist_is_empty(&txn->changes));
 
            /*
             * No need to care about TLIs here, only used during a single run,
             * so each LSN only maps to a specific WAL record.
             */
            ReorderBufferSerializedPath(path, MyReplicationSlot, txn->xid,
                                        *segno);
 
            *fd = PathNameOpenFile(path, O_RDONLY | PG_BINARY);
 
            /* No harm in resetting the offset even in case of failure */
            file->curOffset = 0;
 
            if (*fd < 0 && errno == ENOENT)
            {
                *fd = -1;
                (*segno)++;
                continue;
            }
            else if (*fd < 0)
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not open file \"%s\": %m",
                                path)));
        }
 
        /*
         * Read the statically sized part of a change which has information
         * about the total size. If we couldn't read a record, we're at the
         * end of this file.
         */
        ReorderBufferSerializeReserve(rb, sizeof(ReorderBufferDiskChange));
        readBytes = FileRead(file->vfd, rb->outbuf,
                             sizeof(ReorderBufferDiskChange),
                             file->curOffset, WAIT_EVENT_REORDER_BUFFER_READ);
 
        /* eof */
        if (readBytes == 0)
        {
            FileClose(*fd);
            *fd = -1;
            (*segno)++;
            continue;
        }
        else if (readBytes < 0)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not read from reorderbuffer spill file: %m")));
        else if (readBytes != sizeof(ReorderBufferDiskChange))
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not read from reorderbuffer spill file: read %d instead of %u bytes",
                            readBytes,
                            (uint32) sizeof(ReorderBufferDiskChange))));
 
        file->curOffset += readBytes;
 
        ondisk = (ReorderBufferDiskChange *) rb->outbuf;
 
        ReorderBufferSerializeReserve(rb,
                                      sizeof(ReorderBufferDiskChange) + ondisk->size);
        ondisk = (ReorderBufferDiskChange *) rb->outbuf;
 
        readBytes = FileRead(file->vfd,
                             rb->outbuf + sizeof(ReorderBufferDiskChange),
                             ondisk->size - sizeof(ReorderBufferDiskChange),
                             file->curOffset,
                             WAIT_EVENT_REORDER_BUFFER_READ);
 
        if (readBytes < 0)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not read from reorderbuffer spill file: %m")));
        else if (readBytes != ondisk->size - sizeof(ReorderBufferDiskChange))
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not read from reorderbuffer spill file: read %d instead of %u bytes",
                            readBytes,
                            (uint32) (ondisk->size - sizeof(ReorderBufferDiskChange)))));
 
        file->curOffset += readBytes;
 
        /*
         * ok, read a full change from disk, now restore it into proper
         * in-memory format
         */
        ReorderBufferRestoreChange(rb, txn, rb->outbuf);
        restored++;
    }
 
    return restored;
}
 
/*
 * Convert change from its on-disk format to in-memory format and queue it onto
 * the TXN's ->changes list.
 *
 * Note: although "data" is declared char*, at entry it points to a
 * maxalign'd buffer, making it safe in most of this function to assume
 * that the pointed-to data is suitably aligned for direct access.
 */
static void
ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
                           char *data)
{
    ReorderBufferDiskChange *ondisk;
    ReorderBufferChange *change;
 
    ondisk = (ReorderBufferDiskChange *) data;
 
    change = ReorderBufferGetChange(rb);
 
    /* copy static part */
    memcpy(change, &ondisk->change, sizeof(ReorderBufferChange));
 
    data += sizeof(ReorderBufferDiskChange);
 
    /* restore individual stuff */
    switch (change->action)
    {
            /* fall through these, they're all similar enough */
        case REORDER_BUFFER_CHANGE_INSERT:
        case REORDER_BUFFER_CHANGE_UPDATE:
        case REORDER_BUFFER_CHANGE_DELETE:
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
            if (change->data.tp.oldtuple)
            {
                uint32      tuplelen = ((HeapTuple) data)->t_len;
 
                change->data.tp.oldtuple =
                    ReorderBufferGetTupleBuf(rb, tuplelen - SizeofHeapTupleHeader);
 
                /* restore ->tuple */
                memcpy(change->data.tp.oldtuple, data,
                       sizeof(HeapTupleData));
                data += sizeof(HeapTupleData);
 
                /* reset t_data pointer into the new tuplebuf */
                change->data.tp.oldtuple->t_data =
                    (HeapTupleHeader) ((char *) change->data.tp.oldtuple + HEAPTUPLESIZE);
 
                /* restore tuple data itself */
                memcpy(change->data.tp.oldtuple->t_data, data, tuplelen);
                data += tuplelen;
            }
 
            if (change->data.tp.newtuple)
            {
                /* here, data might not be suitably aligned! */
                uint32      tuplelen;
 
                memcpy(&tuplelen, data + offsetof(HeapTupleData, t_len),
                       sizeof(uint32));
 
                change->data.tp.newtuple =
                    ReorderBufferGetTupleBuf(rb, tuplelen - SizeofHeapTupleHeader);
 
                /* restore ->tuple */
                memcpy(change->data.tp.newtuple, data,
                       sizeof(HeapTupleData));
                data += sizeof(HeapTupleData);
 
                /* reset t_data pointer into the new tuplebuf */
                change->data.tp.newtuple->t_data =
                    (HeapTupleHeader) ((char *) change->data.tp.newtuple + HEAPTUPLESIZE);
 
                /* restore tuple data itself */
                memcpy(change->data.tp.newtuple->t_data, data, tuplelen);
                data += tuplelen;
            }
 
            break;
        case REORDER_BUFFER_CHANGE_MESSAGE:
            {
                Size        prefix_size;
 
                /* read prefix */
                memcpy(&prefix_size, data, sizeof(Size));
                data += sizeof(Size);
                change->data.msg.prefix = MemoryContextAlloc(rb->context,
                                                             prefix_size);
                memcpy(change->data.msg.prefix, data, prefix_size);
                Assert(change->data.msg.prefix[prefix_size - 1] == '\0');
                data += prefix_size;
 
                /* read the message */
                memcpy(&change->data.msg.message_size, data, sizeof(Size));
                data += sizeof(Size);
                change->data.msg.message = MemoryContextAlloc(rb->context,
                                                              change->data.msg.message_size);
                memcpy(change->data.msg.message, data,
                       change->data.msg.message_size);
                data += change->data.msg.message_size;
 
                break;
            }
        case REORDER_BUFFER_CHANGE_INVALIDATION:
            {
                Size        inval_size = sizeof(SharedInvalidationMessage) *
                    change->data.inval.ninvalidations;
 
                change->data.inval.invalidations =
                    MemoryContextAlloc(rb->context, inval_size);
 
                /* read the message */
                memcpy(change->data.inval.invalidations, data, inval_size);
 
                break;
            }
        case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
            {
                Snapshot    oldsnap;
                Snapshot    newsnap;
                Size        size;
 
                oldsnap = (Snapshot) data;
 
                size = sizeof(SnapshotData) +
                    sizeof(TransactionId) * oldsnap->xcnt +
                    sizeof(TransactionId) * (oldsnap->subxcnt + 0);
 
                change->data.snapshot = MemoryContextAllocZero(rb->context, size);
 
                newsnap = change->data.snapshot;
 
                memcpy(newsnap, data, size);
                newsnap->xip = (TransactionId *)
                    (((char *) newsnap) + sizeof(SnapshotData));
                newsnap->subxip = newsnap->xip + newsnap->xcnt;
                newsnap->copied = true;
                break;
            }
            /* the base struct contains all the data, easy peasy */
        case REORDER_BUFFER_CHANGE_TRUNCATE:
            {
                Oid        *relids;
 
                relids = ReorderBufferGetRelids(rb,
                                                change->data.truncate.nrelids);
                memcpy(relids, data, change->data.truncate.nrelids * sizeof(Oid));
                change->data.truncate.relids = relids;
 
                break;
            }
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
        case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
        case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
        case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
            break;
    }
 
    dlist_push_tail(&txn->changes, &change->node);
    txn->nentries_mem++;
 
    /*
     * Update memory accounting for the restored change.  We need to do this
     * although we don't check the memory limit when restoring the changes in
     * this branch (we only do that when initially queueing the changes after
     * decoding), because we will release the changes later, and that will
     * update the accounting too (subtracting the size from the counters). And
     * we don't want to underflow there.
     */
    ReorderBufferChangeMemoryUpdate(rb, change, NULL, true,
                                    ReorderBufferChangeSize(change));
}
 
/*
 * Remove all on-disk stored for the passed in transaction.
 */
static void
ReorderBufferRestoreCleanup(ReorderBuffer *rb, ReorderBufferTXN *txn)
{
    XLogSegNo   first;
    XLogSegNo   cur;
    XLogSegNo   last;
 
    Assert(txn->first_lsn != InvalidXLogRecPtr);
    Assert(txn->final_lsn != InvalidXLogRecPtr);
 
    XLByteToSeg(txn->first_lsn, first, wal_segment_size);
    XLByteToSeg(txn->final_lsn, last, wal_segment_size);
 
    /* iterate over all possible filenames, and delete them */
    for (cur = first; cur <= last; cur++)
    {
        char        path[MAXPGPATH];
 
        ReorderBufferSerializedPath(path, MyReplicationSlot, txn->xid, cur);
        if (unlink(path) != 0 && errno != ENOENT)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not remove file \"%s\": %m", path)));
    }
}
 
/*
 * Remove any leftover serialized reorder buffers from a slot directory after a
 * prior crash or decoding session exit.
 */
static void
ReorderBufferCleanupSerializedTXNs(const char *slotname)
{
    DIR        *spill_dir;
    struct dirent *spill_de;
    struct stat statbuf;
    char        path[MAXPGPATH * 2 + sizeof(PG_REPLSLOT_DIR)];
 
    sprintf(path, "%s/%s", PG_REPLSLOT_DIR, slotname);
 
    /* we're only handling directories here, skip if it's not ours */
    if (lstat(path, &statbuf) == 0 && !S_ISDIR(statbuf.st_mode))
        return;
 
    spill_dir = AllocateDir(path);
    while ((spill_de = ReadDirExtended(spill_dir, path, INFO)) != NULL)
    {
        /* only look at names that can be ours */
        if (strncmp(spill_de->d_name, "xid", 3) == 0)
        {
            snprintf(path, sizeof(path),
                     "%s/%s/%s", PG_REPLSLOT_DIR, slotname,
                     spill_de->d_name);
 
            if (unlink(path) != 0)
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not remove file \"%s\" during removal of %s/%s/xid*: %m",
                                path, PG_REPLSLOT_DIR, slotname)));
        }
    }
    FreeDir(spill_dir);
}
 
/*
 * Given a replication slot, transaction ID and segment number, fill in the
 * corresponding spill file into 'path', which is a caller-owned buffer of size
 * at least MAXPGPATH.
 */
static void
ReorderBufferSerializedPath(char *path, ReplicationSlot *slot, TransactionId xid,
                            XLogSegNo segno)
{
    XLogRecPtr  recptr;
 
    XLogSegNoOffsetToRecPtr(segno, 0, wal_segment_size, recptr);
 
    snprintf(path, MAXPGPATH, "%s/%s/xid-%u-lsn-%X-%X.spill",
             PG_REPLSLOT_DIR,
             NameStr(MyReplicationSlot->data.name),
             xid, LSN_FORMAT_ARGS(recptr));
}
 
/*
 * Delete all data spilled to disk after we've restarted/crashed. It will be
 * recreated when the respective slots are reused.
 */
void
StartupReorderBuffer(void)
{
    DIR        *logical_dir;
    struct dirent *logical_de;
 
    logical_dir = AllocateDir(PG_REPLSLOT_DIR);
    while ((logical_de = ReadDir(logical_dir, PG_REPLSLOT_DIR)) != NULL)
    {
        if (strcmp(logical_de->d_name, ".") == 0 ||
            strcmp(logical_de->d_name, "..") == 0)
            continue;
 
        /* if it cannot be a slot, skip the directory */
        if (!ReplicationSlotValidateName(logical_de->d_name, DEBUG2))
            continue;
 
        /*
         * ok, has to be a surviving logical slot, iterate and delete
         * everything starting with xid-*
         */
        ReorderBufferCleanupSerializedTXNs(logical_de->d_name);
    }
    FreeDir(logical_dir);
}
 
/* ---------------------------------------
 * toast reassembly support
 * ---------------------------------------
 */
 
/*
 * Initialize per tuple toast reconstruction support.
 */
static void
ReorderBufferToastInitHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
{
    HASHCTL     hash_ctl;
 
    Assert(txn->toast_hash == NULL);
 
    hash_ctl.keysize = sizeof(Oid);
    hash_ctl.entrysize = sizeof(ReorderBufferToastEnt);
    hash_ctl.hcxt = rb->context;
    txn->toast_hash = hash_create("ReorderBufferToastHash", 5, &hash_ctl,
                                  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
}
 
/*
 * Per toast-chunk handling for toast reconstruction
 *
 * Appends a toast chunk so we can reconstruct it when the tuple "owning" the
 * toasted Datum comes along.
 */
static void
ReorderBufferToastAppendChunk(ReorderBuffer *rb, ReorderBufferTXN *txn,
                              Relation relation, ReorderBufferChange *change)
{
    ReorderBufferToastEnt *ent;
    HeapTuple   newtup;
    bool        found;
    int32       chunksize;
    bool        isnull;
    Pointer     chunk;
    TupleDesc   desc = RelationGetDescr(relation);
    Oid         chunk_id;
    int32       chunk_seq;
 
    if (txn->toast_hash == NULL)
        ReorderBufferToastInitHash(rb, txn);
 
    Assert(IsToastRelation(relation));
 
    newtup = change->data.tp.newtuple;
    chunk_id = DatumGetObjectId(fastgetattr(newtup, 1, desc, &isnull));
    Assert(!isnull);
    chunk_seq = DatumGetInt32(fastgetattr(newtup, 2, desc, &isnull));
    Assert(!isnull);
 
    ent = (ReorderBufferToastEnt *)
        hash_search(txn->toast_hash, &chunk_id, HASH_ENTER, &found);
 
    if (!found)
    {
        Assert(ent->chunk_id == chunk_id);
        ent->num_chunks = 0;
        ent->last_chunk_seq = 0;
        ent->size = 0;
        ent->reconstructed = NULL;
        dlist_init(&ent->chunks);
 
        if (chunk_seq != 0)
            elog(ERROR, "got sequence entry %d for toast chunk %u instead of seq 0",
                 chunk_seq, chunk_id);
    }
    else if (found && chunk_seq != ent->last_chunk_seq + 1)
        elog(ERROR, "got sequence entry %d for toast chunk %u instead of seq %d",
             chunk_seq, chunk_id, ent->last_chunk_seq + 1);
 
    chunk = DatumGetPointer(fastgetattr(newtup, 3, desc, &isnull));
    Assert(!isnull);
 
    /* calculate size so we can allocate the right size at once later */
    if (!VARATT_IS_EXTENDED(chunk))
        chunksize = VARSIZE(chunk) - VARHDRSZ;
    else if (VARATT_IS_SHORT(chunk))
        /* could happen due to heap_form_tuple doing its thing */
        chunksize = VARSIZE_SHORT(chunk) - VARHDRSZ_SHORT;
    else
        elog(ERROR, "unexpected type of toast chunk");
 
    ent->size += chunksize;
    ent->last_chunk_seq = chunk_seq;
    ent->num_chunks++;
    dlist_push_tail(&ent->chunks, &change->node);
}
 
/*
 * Rejigger change->newtuple to point to in-memory toast tuples instead of
 * on-disk toast tuples that may no longer exist (think DROP TABLE or VACUUM).
 *
 * We cannot replace unchanged toast tuples though, so those will still point
 * to on-disk toast data.
 *
 * While updating the existing change with detoasted tuple data, we need to
 * update the memory accounting info, because the change size will differ.
 * Otherwise the accounting may get out of sync, triggering serialization
 * at unexpected times.
 *
 * We simply subtract size of the change before rejiggering the tuple, and
 * then add the new size. This makes it look like the change was removed
 * and then added back, except it only tweaks the accounting info.
 *
 * In particular it can't trigger serialization, which would be pointless
 * anyway as it happens during commit processing right before handing
 * the change to the output plugin.
 */
static void
ReorderBufferToastReplace(ReorderBuffer *rb, ReorderBufferTXN *txn,
                          Relation relation, ReorderBufferChange *change)
{
    TupleDesc   desc;
    int         natt;
    Datum      *attrs;
    bool       *isnull;
    bool       *free;
    HeapTuple   tmphtup;
    Relation    toast_rel;
    TupleDesc   toast_desc;
    MemoryContext oldcontext;
    HeapTuple   newtup;
    Size        old_size;
 
    /* no toast tuples changed */
    if (txn->toast_hash == NULL)
        return;
 
    /*
     * We're going to modify the size of the change. So, to make sure the
     * accounting is correct we record the current change size and then after
     * re-computing the change we'll subtract the recorded size and then
     * re-add the new change size at the end. We don't immediately subtract
     * the old size because if there is any error before we add the new size,
     * we will release the changes and that will update the accounting info
     * (subtracting the size from the counters). And we don't want to
     * underflow there.
     */
    old_size = ReorderBufferChangeSize(change);
 
    oldcontext = MemoryContextSwitchTo(rb->context);
 
    /* we should only have toast tuples in an INSERT or UPDATE */
    Assert(change->data.tp.newtuple);
 
    desc = RelationGetDescr(relation);
 
    toast_rel = RelationIdGetRelation(relation->rd_rel->reltoastrelid);
    if (!RelationIsValid(toast_rel))
        elog(ERROR, "could not open toast relation with OID %u (base relation \"%s\")",
             relation->rd_rel->reltoastrelid, RelationGetRelationName(relation));
 
    toast_desc = RelationGetDescr(toast_rel);
 
    /* should we allocate from stack instead? */
    attrs = palloc0(sizeof(Datum) * desc->natts);
    isnull = palloc0(sizeof(bool) * desc->natts);
    free = palloc0(sizeof(bool) * desc->natts);
 
    newtup = change->data.tp.newtuple;
 
    heap_deform_tuple(newtup, desc, attrs, isnull);
 
    for (natt = 0; natt < desc->natts; natt++)
    {
        Form_pg_attribute attr = TupleDescAttr(desc, natt);
        ReorderBufferToastEnt *ent;
        struct varlena *varlena;
 
        /* va_rawsize is the size of the original datum -- including header */
        struct varatt_external toast_pointer;
        struct varatt_indirect redirect_pointer;
        struct varlena *new_datum = NULL;
        struct varlena *reconstructed;
        dlist_iter  it;
        Size        data_done = 0;
 
        /* system columns aren't toasted */
        if (attr->attnum < 0)
            continue;
 
        if (attr->attisdropped)
            continue;
 
        /* not a varlena datatype */
        if (attr->attlen != -1)
            continue;
 
        /* no data */
        if (isnull[natt])
            continue;
 
        /* ok, we know we have a toast datum */
        varlena = (struct varlena *) DatumGetPointer(attrs[natt]);
 
        /* no need to do anything if the tuple isn't external */
        if (!VARATT_IS_EXTERNAL(varlena))
            continue;
 
        VARATT_EXTERNAL_GET_POINTER(toast_pointer, varlena);
 
        /*
         * Check whether the toast tuple changed, replace if so.
         */
        ent = (ReorderBufferToastEnt *)
            hash_search(txn->toast_hash,
                        &toast_pointer.va_valueid,
                        HASH_FIND,
                        NULL);
        if (ent == NULL)
            continue;
 
        new_datum =
            (struct varlena *) palloc0(INDIRECT_POINTER_SIZE);
 
        free[natt] = true;
 
        reconstructed = palloc0(toast_pointer.va_rawsize);
 
        ent->reconstructed = reconstructed;
 
        /* stitch toast tuple back together from its parts */
        dlist_foreach(it, &ent->chunks)
        {
            bool        cisnull;
            ReorderBufferChange *cchange;
            HeapTuple   ctup;
            Pointer     chunk;
 
            cchange = dlist_container(ReorderBufferChange, node, it.cur);
            ctup = cchange->data.tp.newtuple;
            chunk = DatumGetPointer(fastgetattr(ctup, 3, toast_desc, &cisnull));
 
            Assert(!cisnull);
            Assert(!VARATT_IS_EXTERNAL(chunk));
            Assert(!VARATT_IS_SHORT(chunk));
 
            memcpy(VARDATA(reconstructed) + data_done,
                   VARDATA(chunk),
                   VARSIZE(chunk) - VARHDRSZ);
            data_done += VARSIZE(chunk) - VARHDRSZ;
        }
        Assert(data_done == VARATT_EXTERNAL_GET_EXTSIZE(toast_pointer));
 
        /* make sure its marked as compressed or not */
        if (VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
            SET_VARSIZE_COMPRESSED(reconstructed, data_done + VARHDRSZ);
        else
            SET_VARSIZE(reconstructed, data_done + VARHDRSZ);
 
        memset(&redirect_pointer, 0, sizeof(redirect_pointer));
        redirect_pointer.pointer = reconstructed;
 
        SET_VARTAG_EXTERNAL(new_datum, VARTAG_INDIRECT);
        memcpy(VARDATA_EXTERNAL(new_datum), &redirect_pointer,
               sizeof(redirect_pointer));
 
        attrs[natt] = PointerGetDatum(new_datum);
    }
 
    /*
     * Build tuple in separate memory & copy tuple back into the tuplebuf
     * passed to the output plugin. We can't directly heap_fill_tuple() into
     * the tuplebuf because attrs[] will point back into the current content.
     */
    tmphtup = heap_form_tuple(desc, attrs, isnull);
    Assert(newtup->t_len <= MaxHeapTupleSize);
    Assert(newtup->t_data == (HeapTupleHeader) ((char *) newtup + HEAPTUPLESIZE));
 
    memcpy(newtup->t_data, tmphtup->t_data, tmphtup->t_len);
    newtup->t_len = tmphtup->t_len;
 
    /*
     * free resources we won't further need, more persistent stuff will be
     * free'd in ReorderBufferToastReset().
     */
    RelationClose(toast_rel);
    pfree(tmphtup);
    for (natt = 0; natt < desc->natts; natt++)
    {
        if (free[natt])
            pfree(DatumGetPointer(attrs[natt]));
    }
    pfree(attrs);
    pfree(free);
    pfree(isnull);
 
    MemoryContextSwitchTo(oldcontext);
 
    /* subtract the old change size */
    ReorderBufferChangeMemoryUpdate(rb, change, NULL, false, old_size);
    /* now add the change back, with the correct size */
    ReorderBufferChangeMemoryUpdate(rb, change, NULL, true,
                                    ReorderBufferChangeSize(change));
}
 
/*
 * Free all resources allocated for toast reconstruction.
 */
static void
ReorderBufferToastReset(ReorderBuffer *rb, ReorderBufferTXN *txn)
{
    HASH_SEQ_STATUS hstat;
    ReorderBufferToastEnt *ent;
 
    if (txn->toast_hash == NULL)
        return;
 
    /* sequentially walk over the hash and free everything */
    hash_seq_init(&hstat, txn->toast_hash);
    while ((ent = (ReorderBufferToastEnt *) hash_seq_search(&hstat)) != NULL)
    {
        dlist_mutable_iter it;
 
        if (ent->reconstructed != NULL)
            pfree(ent->reconstructed);
 
        dlist_foreach_modify(it, &ent->chunks)
        {
            ReorderBufferChange *change =
                dlist_container(ReorderBufferChange, node, it.cur);
 
            dlist_delete(&change->node);
            ReorderBufferReturnChange(rb, change, true);
        }
    }
 
    hash_destroy(txn->toast_hash);
    txn->toast_hash = NULL;
}
 
 
/* ---------------------------------------
 * Visibility support for logical decoding
 *
 *
 * Lookup actual cmin/cmax values when using decoding snapshot. We can't
 * always rely on stored cmin/cmax values because of two scenarios:
 *
 * * A tuple got changed multiple times during a single transaction and thus
 *   has got a combo CID. Combo CIDs are only valid for the duration of a
 *   single transaction.
 * * A tuple with a cmin but no cmax (and thus no combo CID) got
 *   deleted/updated in another transaction than the one which created it
 *   which we are looking at right now. As only one of cmin, cmax or combo CID
 *   is actually stored in the heap we don't have access to the value we
 *   need anymore.
 *
 * To resolve those problems we have a per-transaction hash of (cmin,
 * cmax) tuples keyed by (relfilelocator, ctid) which contains the actual
 * (cmin, cmax) values. That also takes care of combo CIDs by simply
 * not caring about them at all. As we have the real cmin/cmax values
 * combo CIDs aren't interesting.
 *
 * As we only care about catalog tuples here the overhead of this
 * hashtable should be acceptable.
 *
 * Heap rewrites complicate this a bit, check rewriteheap.c for
 * details.
 * -------------------------------------------------------------------------
 */
 
/* struct for sorting mapping files by LSN efficiently */
typedef struct RewriteMappingFile
{
    XLogRecPtr  lsn;
    char        fname[MAXPGPATH];
} RewriteMappingFile;
 
#ifdef NOT_USED
static void
DisplayMapping(HTAB *tuplecid_data)
{
    HASH_SEQ_STATUS hstat;
    ReorderBufferTupleCidEnt *ent;
 
    hash_seq_init(&hstat, tuplecid_data);
    while ((ent = (ReorderBufferTupleCidEnt *) hash_seq_search(&hstat)) != NULL)
    {
        elog(DEBUG3, "mapping: node: %u/%u/%u tid: %u/%u cmin: %u, cmax: %u",
             ent->key.rlocator.dbOid,
             ent->key.rlocator.spcOid,
             ent->key.rlocator.relNumber,
             ItemPointerGetBlockNumber(&ent->key.tid),
             ItemPointerGetOffsetNumber(&ent->key.tid),
             ent->cmin,
             ent->cmax
            );
    }
}
#endif
 
/*
 * Apply a single mapping file to tuplecid_data.
 *
 * The mapping file has to have been verified to be a) committed b) for our
 * transaction c) applied in LSN order.
 */
static void
ApplyLogicalMappingFile(HTAB *tuplecid_data, Oid relid, const char *fname)
{
    char        path[MAXPGPATH];
    int         fd;
    int         readBytes;
    LogicalRewriteMappingData map;
 
    sprintf(path, "%s/%s", PG_LOGICAL_MAPPINGS_DIR, fname);
    fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
    if (fd < 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not open file \"%s\": %m", path)));
 
    while (true)
    {
        ReorderBufferTupleCidKey key;
        ReorderBufferTupleCidEnt *ent;
        ReorderBufferTupleCidEnt *new_ent;
        bool        found;
 
        /* be careful about padding */
        memset(&key, 0, sizeof(ReorderBufferTupleCidKey));
 
        /* read all mappings till the end of the file */
        pgstat_report_wait_start(WAIT_EVENT_REORDER_LOGICAL_MAPPING_READ);
        readBytes = read(fd, &map, sizeof(LogicalRewriteMappingData));
        pgstat_report_wait_end();
 
        if (readBytes < 0)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not read file \"%s\": %m",
                            path)));
        else if (readBytes == 0)    /* EOF */
            break;
        else if (readBytes != sizeof(LogicalRewriteMappingData))
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not read from file \"%s\": read %d instead of %d bytes",
                            path, readBytes,
                            (int32) sizeof(LogicalRewriteMappingData))));
 
        key.rlocator = map.old_locator;
        ItemPointerCopy(&map.old_tid,
                        &key.tid);
 
 
        ent = (ReorderBufferTupleCidEnt *)
            hash_search(tuplecid_data, &key, HASH_FIND, NULL);
 
        /* no existing mapping, no need to update */
        if (!ent)
            continue;
 
        key.rlocator = map.new_locator;
        ItemPointerCopy(&map.new_tid,
                        &key.tid);
 
        new_ent = (ReorderBufferTupleCidEnt *)
            hash_search(tuplecid_data, &key, HASH_ENTER, &found);
 
        if (found)
        {
            /*
             * Make sure the existing mapping makes sense. We sometime update
             * old records that did not yet have a cmax (e.g. pg_class' own
             * entry while rewriting it) during rewrites, so allow that.
             */
            Assert(ent->cmin == InvalidCommandId || ent->cmin == new_ent->cmin);
            Assert(ent->cmax == InvalidCommandId || ent->cmax == new_ent->cmax);
        }
        else
        {
            /* update mapping */
            new_ent->cmin = ent->cmin;
            new_ent->cmax = ent->cmax;
            new_ent->combocid = ent->combocid;
        }
    }
 
    if (CloseTransientFile(fd) != 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not close file \"%s\": %m", path)));
}
 
 
/*
 * Check whether the TransactionId 'xid' is in the pre-sorted array 'xip'.
 */
static bool
TransactionIdInArray(TransactionId xid, TransactionId *xip, Size num)
{
    return bsearch(&xid, xip, num,
                   sizeof(TransactionId), xidComparator) != NULL;
}
 
/*
 * list_sort() comparator for sorting RewriteMappingFiles in LSN order.
 */
static int
file_sort_by_lsn(const ListCell *a_p, const ListCell *b_p)
{
    RewriteMappingFile *a = (RewriteMappingFile *) lfirst(a_p);
    RewriteMappingFile *b = (RewriteMappingFile *) lfirst(b_p);
 
    return pg_cmp_u64(a->lsn, b->lsn);
}
 
/*
 * Apply any existing logical remapping files if there are any targeted at our
 * transaction for relid.
 */
static void
UpdateLogicalMappings(HTAB *tuplecid_data, Oid relid, Snapshot snapshot)
{
    DIR        *mapping_dir;
    struct dirent *mapping_de;
    List       *files = NIL;
    ListCell   *file;
    Oid         dboid = IsSharedRelation(relid) ? InvalidOid : MyDatabaseId;
 
    mapping_dir = AllocateDir(PG_LOGICAL_MAPPINGS_DIR);
    while ((mapping_de = ReadDir(mapping_dir, PG_LOGICAL_MAPPINGS_DIR)) != NULL)
    {
        Oid         f_dboid;
        Oid         f_relid;
        TransactionId f_mapped_xid;
        TransactionId f_create_xid;
        XLogRecPtr  f_lsn;
        uint32      f_hi,
                    f_lo;
        RewriteMappingFile *f;
 
        if (strcmp(mapping_de->d_name, ".") == 0 ||
            strcmp(mapping_de->d_name, "..") == 0)
            continue;
 
        /* Ignore files that aren't ours */
        if (strncmp(mapping_de->d_name, "map-", 4) != 0)
            continue;
 
        if (sscanf(mapping_de->d_name, LOGICAL_REWRITE_FORMAT,
                   &f_dboid, &f_relid, &f_hi, &f_lo,
                   &f_mapped_xid, &f_create_xid) != 6)
            elog(ERROR, "could not parse filename \"%s\"", mapping_de->d_name);
 
        f_lsn = ((uint64) f_hi) << 32 | f_lo;
 
        /* mapping for another database */
        if (f_dboid != dboid)
            continue;
 
        /* mapping for another relation */
        if (f_relid != relid)
            continue;
 
        /* did the creating transaction abort? */
        if (!TransactionIdDidCommit(f_create_xid))
            continue;
 
        /* not for our transaction */
        if (!TransactionIdInArray(f_mapped_xid, snapshot->subxip, snapshot->subxcnt))
            continue;
 
        /* ok, relevant, queue for apply */
        f = palloc(sizeof(RewriteMappingFile));
        f->lsn = f_lsn;
        strcpy(f->fname, mapping_de->d_name);
        files = lappend(files, f);
    }
    FreeDir(mapping_dir);
 
    /* sort files so we apply them in LSN order */
    list_sort(files, file_sort_by_lsn);
 
    foreach(file, files)
    {
        RewriteMappingFile *f = (RewriteMappingFile *) lfirst(file);
 
        elog(DEBUG1, "applying mapping: \"%s\" in %u", f->fname,
             snapshot->subxip[0]);
        ApplyLogicalMappingFile(tuplecid_data, relid, f->fname);
        pfree(f);
    }
}
 
/*
 * Lookup cmin/cmax of a tuple, during logical decoding where we can't rely on
 * combo CIDs.
 */
bool
ResolveCminCmaxDuringDecoding(HTAB *tuplecid_data,
                              Snapshot snapshot,
                              HeapTuple htup, Buffer buffer,
                              CommandId *cmin, CommandId *cmax)
{
    ReorderBufferTupleCidKey key;
    ReorderBufferTupleCidEnt *ent;
    ForkNumber  forkno;
    BlockNumber blockno;
    bool        updated_mapping = false;
 
    /*
     * Return unresolved if tuplecid_data is not valid.  That's because when
     * streaming in-progress transactions we may run into tuples with the CID
     * before actually decoding them.  Think e.g. about INSERT followed by
     * TRUNCATE, where the TRUNCATE may not be decoded yet when applying the
     * INSERT.  So in such cases, we assume the CID is from the future
     * command.
     */
    if (tuplecid_data == NULL)
        return false;
 
    /* be careful about padding */
    memset(&key, 0, sizeof(key));
 
    Assert(!BufferIsLocal(buffer));
 
    /*
     * get relfilelocator from the buffer, no convenient way to access it
     * other than that.
     */
    BufferGetTag(buffer, &key.rlocator, &forkno, &blockno);
 
    /* tuples can only be in the main fork */
    Assert(forkno == MAIN_FORKNUM);
    Assert(blockno == ItemPointerGetBlockNumber(&htup->t_self));
 
    ItemPointerCopy(&htup->t_self,
                    &key.tid);
 
restart:
    ent = (ReorderBufferTupleCidEnt *)
        hash_search(tuplecid_data, &key, HASH_FIND, NULL);
 
    /*
     * failed to find a mapping, check whether the table was rewritten and
     * apply mapping if so, but only do that once - there can be no new
     * mappings while we are in here since we have to hold a lock on the
     * relation.
     */
    if (ent == NULL && !updated_mapping)
    {
        UpdateLogicalMappings(tuplecid_data, htup->t_tableOid, snapshot);
        /* now check but don't update for a mapping again */
        updated_mapping = true;
        goto restart;
    }
    else if (ent == NULL)
        return false;
 
    if (cmin)
        *cmin = ent->cmin;
    if (cmax)
        *cmax = ent->cmax;
    return true;
}