pgoutput.c

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/*-------------------------------------------------------------------------
 *
 * pgoutput.c
 *      Logical Replication output plugin
 *
 * Copyright (c) 2012-2020, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        src/backend/replication/pgoutput/pgoutput.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/tupconvert.h"
#include "catalog/partition.h"
#include "catalog/pg_publication.h"
#include "commands/defrem.h"
#include "fmgr.h"
#include "replication/logical.h"
#include "replication/logicalproto.h"
#include "replication/origin.h"
#include "replication/pgoutput.h"
#include "utils/int8.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/syscache.h"
#include "utils/varlena.h"

PG_MODULE_MAGIC;

extern void _PG_output_plugin_init(OutputPluginCallbacks *cb);

static void pgoutput_startup(LogicalDecodingContext *ctx,
                             OutputPluginOptions *opt, bool is_init);
static void pgoutput_shutdown(LogicalDecodingContext *ctx);
static void pgoutput_begin_txn(LogicalDecodingContext *ctx,
                               ReorderBufferTXN *txn);
static void pgoutput_commit_txn(LogicalDecodingContext *ctx,
                                ReorderBufferTXN *txn, XLogRecPtr commit_lsn);
static void pgoutput_change(LogicalDecodingContext *ctx,
                            ReorderBufferTXN *txn, Relation rel,
                            ReorderBufferChange *change);
static void pgoutput_truncate(LogicalDecodingContext *ctx,
                              ReorderBufferTXN *txn, int nrelations, Relation relations[],
                              ReorderBufferChange *change);
static bool pgoutput_origin_filter(LogicalDecodingContext *ctx,
                                   RepOriginId origin_id);
static void pgoutput_stream_start(struct LogicalDecodingContext *ctx,
                                  ReorderBufferTXN *txn);
static void pgoutput_stream_stop(struct LogicalDecodingContext *ctx,
                                 ReorderBufferTXN *txn);
static void pgoutput_stream_abort(struct LogicalDecodingContext *ctx,
                                  ReorderBufferTXN *txn,
                                  XLogRecPtr abort_lsn);
static void pgoutput_stream_commit(struct LogicalDecodingContext *ctx,
                                   ReorderBufferTXN *txn,
                                   XLogRecPtr commit_lsn);

static bool publications_valid;
static bool in_streaming;

static List *LoadPublications(List *pubnames);
static void publication_invalidation_cb(Datum arg, int cacheid,
                                        uint32 hashvalue);
static void send_relation_and_attrs(Relation relation, TransactionId xid,
                                    LogicalDecodingContext *ctx);

/*
 * Entry in the map used to remember which relation schemas we sent.
 *
 * The schema_sent flag determines if the current schema record was already
 * sent to the subscriber (in which case we don't need to send it again).
 *
 * The schema cache on downstream is however updated only at commit time,
 * and with streamed transactions the commit order may be different from
 * the order the transactions are sent in. Also, the (sub) transactions
 * might get aborted so we need to send the schema for each (sub) transaction
 * so that we don't lose the schema information on abort. For handling this,
 * we maintain the list of xids (streamed_txns) for those we have already sent
 * the schema.
 *
 * For partitions, 'pubactions' considers not only the table's own
 * publications, but also those of all of its ancestors.
 */
typedef struct RelationSyncEntry
{
    Oid         relid;          /* relation oid */

    /*
     * Did we send the schema?  If ancestor relid is set, its schema must also
     * have been sent for this to be true.
     */
    bool        schema_sent;
    List       *streamed_txns;  /* streamed toplevel transactions with this
                                 * schema */

    bool        replicate_valid;
    PublicationActions pubactions;

    /*
     * OID of the relation to publish changes as.  For a partition, this may
     * be set to one of its ancestors whose schema will be used when
     * replicating changes, if publish_via_partition_root is set for the
     * publication.
     */
    Oid         publish_as_relid;

    /*
     * Map used when replicating using an ancestor's schema to convert tuples
     * from partition's type to the ancestor's; NULL if publish_as_relid is
     * same as 'relid' or if unnecessary due to partition and the ancestor
     * having identical TupleDesc.
     */
    TupleConversionMap *map;
} RelationSyncEntry;

/* Map used to remember which relation schemas we sent. */
static HTAB *RelationSyncCache = NULL;

static void init_rel_sync_cache(MemoryContext decoding_context);
static void cleanup_rel_sync_cache(TransactionId xid, bool is_commit);
static RelationSyncEntry *get_rel_sync_entry(PGOutputData *data, Oid relid);
static void rel_sync_cache_relation_cb(Datum arg, Oid relid);
static void rel_sync_cache_publication_cb(Datum arg, int cacheid,
                                          uint32 hashvalue);
static void set_schema_sent_in_streamed_txn(RelationSyncEntry *entry,
                                            TransactionId xid);
static bool get_schema_sent_in_streamed_txn(RelationSyncEntry *entry,
                                            TransactionId xid);

/*
 * Specify output plugin callbacks
 */
void
_PG_output_plugin_init(OutputPluginCallbacks *cb)
{
    AssertVariableIsOfType(&_PG_output_plugin_init, LogicalOutputPluginInit);

    cb->startup_cb = pgoutput_startup;
    cb->begin_cb = pgoutput_begin_txn;
    cb->change_cb = pgoutput_change;
    cb->truncate_cb = pgoutput_truncate;
    cb->commit_cb = pgoutput_commit_txn;
    cb->filter_by_origin_cb = pgoutput_origin_filter;
    cb->shutdown_cb = pgoutput_shutdown;

    /* transaction streaming */
    cb->stream_start_cb = pgoutput_stream_start;
    cb->stream_stop_cb = pgoutput_stream_stop;
    cb->stream_abort_cb = pgoutput_stream_abort;
    cb->stream_commit_cb = pgoutput_stream_commit;
    cb->stream_change_cb = pgoutput_change;
    cb->stream_truncate_cb = pgoutput_truncate;
}

static void
parse_output_parameters(List *options, uint32 *protocol_version,
                        List **publication_names, bool *binary,
                        bool *enable_streaming)
{
    ListCell   *lc;
    bool        protocol_version_given = false;
    bool        publication_names_given = false;
    bool        binary_option_given = false;
    bool        streaming_given = false;

    *binary = false;

    foreach(lc, options)
    {
        DefElem    *defel = (DefElem *) lfirst(lc);

        Assert(defel->arg == NULL || IsA(defel->arg, String));

        /* Check each param, whether or not we recognize it */
        if (strcmp(defel->defname, "proto_version") == 0)
        {
            int64       parsed;

            if (protocol_version_given)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options")));
            protocol_version_given = true;

            if (!scanint8(strVal(defel->arg), true, &parsed))
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("invalid proto_version")));

            if (parsed > PG_UINT32_MAX || parsed < 0)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("proto_version \"%s\" out of range",
                                strVal(defel->arg))));

            *protocol_version = (uint32) parsed;
        }
        else if (strcmp(defel->defname, "publication_names") == 0)
        {
            if (publication_names_given)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options")));
            publication_names_given = true;

            if (!SplitIdentifierString(strVal(defel->arg), ',',
                                       publication_names))
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_NAME),
                         errmsg("invalid publication_names syntax")));
        }
        else if (strcmp(defel->defname, "binary") == 0)
        {
            if (binary_option_given)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options")));
            binary_option_given = true;

            *binary = defGetBoolean(defel);
        }
        else if (strcmp(defel->defname, "streaming") == 0)
        {
            if (streaming_given)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options")));
            streaming_given = true;

            *enable_streaming = defGetBoolean(defel);
        }
        else
            elog(ERROR, "unrecognized pgoutput option: %s", defel->defname);
    }
}

/*
 * Initialize this plugin
 */
static void
pgoutput_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
                 bool is_init)
{
    bool        enable_streaming = false;
    PGOutputData *data = palloc0(sizeof(PGOutputData));

    /* Create our memory context for private allocations. */
    data->context = AllocSetContextCreate(ctx->context,
                                          "logical replication output context",
                                          ALLOCSET_DEFAULT_SIZES);

    ctx->output_plugin_private = data;

    /* This plugin uses binary protocol. */
    opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;

    /*
     * This is replication start and not slot initialization.
     *
     * Parse and validate options passed by the client.
     */
    if (!is_init)
    {
        /* Parse the params and ERROR if we see any we don't recognize */
        parse_output_parameters(ctx->output_plugin_options,
                                &data->protocol_version,
                                &data->publication_names,
                                &data->binary,
                                &enable_streaming);

        /* Check if we support requested protocol */
        if (data->protocol_version > LOGICALREP_PROTO_MAX_VERSION_NUM)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("client sent proto_version=%d but we only support protocol %d or lower",
                            data->protocol_version, LOGICALREP_PROTO_MAX_VERSION_NUM)));

        if (data->protocol_version < LOGICALREP_PROTO_MIN_VERSION_NUM)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("client sent proto_version=%d but we only support protocol %d or higher",
                            data->protocol_version, LOGICALREP_PROTO_MIN_VERSION_NUM)));

        if (list_length(data->publication_names) < 1)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("publication_names parameter missing")));

        /*
         * Decide whether to enable streaming. It is disabled by default, in
         * which case we just update the flag in decoding context. Otherwise
         * we only allow it with sufficient version of the protocol, and when
         * the output plugin supports it.
         */
        if (!enable_streaming)
            ctx->streaming = false;
        else if (data->protocol_version < LOGICALREP_PROTO_STREAM_VERSION_NUM)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("requested proto_version=%d does not support streaming, need %d or higher",
                            data->protocol_version, LOGICALREP_PROTO_STREAM_VERSION_NUM)));
        else if (!ctx->streaming)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("streaming requested, but not supported by output plugin")));

        /* Also remember we're currently not streaming any transaction. */
        in_streaming = false;

        /* Init publication state. */
        data->publications = NIL;
        publications_valid = false;
        CacheRegisterSyscacheCallback(PUBLICATIONOID,
                                      publication_invalidation_cb,
                                      (Datum) 0);

        /* Initialize relation schema cache. */
        init_rel_sync_cache(CacheMemoryContext);
    }
    else
    {
        /* Disable the streaming during the slot initialization mode. */
        ctx->streaming = false;
    }
}

/*
 * BEGIN callback
 */
static void
pgoutput_begin_txn(LogicalDecodingContext *ctx, ReorderBufferTXN *txn)
{
    bool        send_replication_origin = txn->origin_id != InvalidRepOriginId;

    OutputPluginPrepareWrite(ctx, !send_replication_origin);
    logicalrep_write_begin(ctx->out, txn);

    if (send_replication_origin)
    {
        char       *origin;

        /* Message boundary */
        OutputPluginWrite(ctx, false);
        OutputPluginPrepareWrite(ctx, true);

        /*----------
         * XXX: which behaviour do we want here?
         *
         * Alternatives:
         *  - don't send origin message if origin name not found
         *    (that's what we do now)
         *  - throw error - that will break replication, not good
         *  - send some special "unknown" origin
         *----------
         */
        if (replorigin_by_oid(txn->origin_id, true, &origin))
            logicalrep_write_origin(ctx->out, origin, txn->origin_lsn);
    }

    OutputPluginWrite(ctx, true);
}

/*
 * COMMIT callback
 */
static void
pgoutput_commit_txn(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
                    XLogRecPtr commit_lsn)
{
    OutputPluginUpdateProgress(ctx);

    OutputPluginPrepareWrite(ctx, true);
    logicalrep_write_commit(ctx->out, txn, commit_lsn);
    OutputPluginWrite(ctx, true);
}

/*
 * Write the current schema of the relation and its ancestor (if any) if not
 * done yet.
 */
static void
maybe_send_schema(LogicalDecodingContext *ctx,
                  ReorderBufferTXN *txn, ReorderBufferChange *change,
                  Relation relation, RelationSyncEntry *relentry)
{
    bool        schema_sent;
    TransactionId xid = InvalidTransactionId;
    TransactionId topxid = InvalidTransactionId;

    /*
     * Remember XID of the (sub)transaction for the change. We don't care if
     * it's top-level transaction or not (we have already sent that XID in
     * start of the current streaming block).
     *
     * If we're not in a streaming block, just use InvalidTransactionId and
     * the write methods will not include it.
     */
    if (in_streaming)
        xid = change->txn->xid;

    if (change->txn->toptxn)
        topxid = change->txn->toptxn->xid;
    else
        topxid = xid;

    /*
     * Do we need to send the schema? We do track streamed transactions
     * separately, because those may be applied later (and the regular
     * transactions won't see their effects until then) and in an order that
     * we don't know at this point.
     *
     * XXX There is a scope of optimization here. Currently, we always send
     * the schema first time in a streaming transaction but we can probably
     * avoid that by checking 'relentry->schema_sent' flag. However, before
     * doing that we need to study its impact on the case where we have a mix
     * of streaming and non-streaming transactions.
     */
    if (in_streaming)
        schema_sent = get_schema_sent_in_streamed_txn(relentry, topxid);
    else
        schema_sent = relentry->schema_sent;

    if (schema_sent)
        return;

    /* If needed, send the ancestor's schema first. */
    if (relentry->publish_as_relid != RelationGetRelid(relation))
    {
        Relation    ancestor = RelationIdGetRelation(relentry->publish_as_relid);
        TupleDesc   indesc = RelationGetDescr(relation);
        TupleDesc   outdesc = RelationGetDescr(ancestor);
        MemoryContext oldctx;

        /* Map must live as long as the session does. */
        oldctx = MemoryContextSwitchTo(CacheMemoryContext);
        relentry->map = convert_tuples_by_name(CreateTupleDescCopy(indesc),
                                               CreateTupleDescCopy(outdesc));
        MemoryContextSwitchTo(oldctx);
        send_relation_and_attrs(ancestor, xid, ctx);
        RelationClose(ancestor);
    }

    send_relation_and_attrs(relation, xid, ctx);

    if (in_streaming)
        set_schema_sent_in_streamed_txn(relentry, topxid);
    else
        relentry->schema_sent = true;
}

/*
 * Sends a relation
 */
static void
send_relation_and_attrs(Relation relation, TransactionId xid,
                        LogicalDecodingContext *ctx)
{
    TupleDesc   desc = RelationGetDescr(relation);
    int         i;

    /*
     * Write out type info if needed.  We do that only for user-created types.
     * We use FirstGenbkiObjectId as the cutoff, so that we only consider
     * objects with hand-assigned OIDs to be "built in", not for instance any
     * function or type defined in the information_schema. This is important
     * because only hand-assigned OIDs can be expected to remain stable across
     * major versions.
     */
    for (i = 0; i < desc->natts; i++)
    {
        Form_pg_attribute att = TupleDescAttr(desc, i);

        if (att->attisdropped || att->attgenerated)
            continue;

        if (att->atttypid < FirstGenbkiObjectId)
            continue;

        OutputPluginPrepareWrite(ctx, false);
        logicalrep_write_typ(ctx->out, xid, att->atttypid);
        OutputPluginWrite(ctx, false);
    }

    OutputPluginPrepareWrite(ctx, false);
    logicalrep_write_rel(ctx->out, xid, relation);
    OutputPluginWrite(ctx, false);
}

/*
 * Sends the decoded DML over wire.
 *
 * This is called both in streaming and non-streaming modes.
 */
static void
pgoutput_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
                Relation relation, ReorderBufferChange *change)
{
    PGOutputData *data = (PGOutputData *) ctx->output_plugin_private;
    MemoryContext old;
    RelationSyncEntry *relentry;
    TransactionId xid = InvalidTransactionId;

    if (!is_publishable_relation(relation))
        return;

    /*
     * Remember the xid for the change in streaming mode. We need to send xid
     * with each change in the streaming mode so that subscriber can make
     * their association and on aborts, it can discard the corresponding
     * changes.
     */
    if (in_streaming)
        xid = change->txn->xid;

    relentry = get_rel_sync_entry(data, RelationGetRelid(relation));

    /* First check the table filter */
    switch (change->action)
    {
        case REORDER_BUFFER_CHANGE_INSERT:
            if (!relentry->pubactions.pubinsert)
                return;
            break;
        case REORDER_BUFFER_CHANGE_UPDATE:
            if (!relentry->pubactions.pubupdate)
                return;
            break;
        case REORDER_BUFFER_CHANGE_DELETE:
            if (!relentry->pubactions.pubdelete)
                return;
            break;
        default:
            Assert(false);
    }

    /* Avoid leaking memory by using and resetting our own context */
    old = MemoryContextSwitchTo(data->context);

    maybe_send_schema(ctx, txn, change, relation, relentry);

    /* Send the data */
    switch (change->action)
    {
        case REORDER_BUFFER_CHANGE_INSERT:
            {
                HeapTuple   tuple = &change->data.tp.newtuple->tuple;

                /* Switch relation if publishing via root. */
                if (relentry->publish_as_relid != RelationGetRelid(relation))
                {
                    Assert(relation->rd_rel->relispartition);
                    relation = RelationIdGetRelation(relentry->publish_as_relid);
                    /* Convert tuple if needed. */
                    if (relentry->map)
                        tuple = execute_attr_map_tuple(tuple, relentry->map);
                }

                OutputPluginPrepareWrite(ctx, true);
                logicalrep_write_insert(ctx->out, xid, relation, tuple,
                                        data->binary);
                OutputPluginWrite(ctx, true);
                break;
            }
        case REORDER_BUFFER_CHANGE_UPDATE:
            {
                HeapTuple   oldtuple = change->data.tp.oldtuple ?
                &change->data.tp.oldtuple->tuple : NULL;
                HeapTuple   newtuple = &change->data.tp.newtuple->tuple;

                /* Switch relation if publishing via root. */
                if (relentry->publish_as_relid != RelationGetRelid(relation))
                {
                    Assert(relation->rd_rel->relispartition);
                    relation = RelationIdGetRelation(relentry->publish_as_relid);
                    /* Convert tuples if needed. */
                    if (relentry->map)
                    {
                        oldtuple = execute_attr_map_tuple(oldtuple, relentry->map);
                        newtuple = execute_attr_map_tuple(newtuple, relentry->map);
                    }
                }

                OutputPluginPrepareWrite(ctx, true);
                logicalrep_write_update(ctx->out, xid, relation, oldtuple,
                                        newtuple, data->binary);
                OutputPluginWrite(ctx, true);
                break;
            }
        case REORDER_BUFFER_CHANGE_DELETE:
            if (change->data.tp.oldtuple)
            {
                HeapTuple   oldtuple = &change->data.tp.oldtuple->tuple;

                /* Switch relation if publishing via root. */
                if (relentry->publish_as_relid != RelationGetRelid(relation))
                {
                    Assert(relation->rd_rel->relispartition);
                    relation = RelationIdGetRelation(relentry->publish_as_relid);
                    /* Convert tuple if needed. */
                    if (relentry->map)
                        oldtuple = execute_attr_map_tuple(oldtuple, relentry->map);
                }

                OutputPluginPrepareWrite(ctx, true);
                logicalrep_write_delete(ctx->out, xid, relation, oldtuple,
                                        data->binary);
                OutputPluginWrite(ctx, true);
            }
            else
                elog(DEBUG1, "didn't send DELETE change because of missing oldtuple");
            break;
        default:
            Assert(false);
    }

    /* Cleanup */
    MemoryContextSwitchTo(old);
    MemoryContextReset(data->context);
}

static void
pgoutput_truncate(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
                  int nrelations, Relation relations[], ReorderBufferChange *change)
{
    PGOutputData *data = (PGOutputData *) ctx->output_plugin_private;
    MemoryContext old;
    RelationSyncEntry *relentry;
    int         i;
    int         nrelids;
    Oid        *relids;
    TransactionId xid = InvalidTransactionId;

    /* Remember the xid for the change in streaming mode. See pgoutput_change. */
    if (in_streaming)
        xid = change->txn->xid;

    old = MemoryContextSwitchTo(data->context);

    relids = palloc0(nrelations * sizeof(Oid));
    nrelids = 0;

    for (i = 0; i < nrelations; i++)
    {
        Relation    relation = relations[i];
        Oid         relid = RelationGetRelid(relation);

        if (!is_publishable_relation(relation))
            continue;

        relentry = get_rel_sync_entry(data, relid);

        if (!relentry->pubactions.pubtruncate)
            continue;

        /*
         * Don't send partitions if the publication wants to send only the
         * root tables through it.
         */
        if (relation->rd_rel->relispartition &&
            relentry->publish_as_relid != relid)
            continue;

        relids[nrelids++] = relid;
        maybe_send_schema(ctx, txn, change, relation, relentry);
    }

    if (nrelids > 0)
    {
        OutputPluginPrepareWrite(ctx, true);
        logicalrep_write_truncate(ctx->out,
                                  xid,
                                  nrelids,
                                  relids,
                                  change->data.truncate.cascade,
                                  change->data.truncate.restart_seqs);
        OutputPluginWrite(ctx, true);
    }

    MemoryContextSwitchTo(old);
    MemoryContextReset(data->context);
}

/*
 * Currently we always forward.
 */
static bool
pgoutput_origin_filter(LogicalDecodingContext *ctx,
                       RepOriginId origin_id)
{
    return false;
}

/*
 * Shutdown the output plugin.
 *
 * Note, we don't need to clean the data->context as it's child context
 * of the ctx->context so it will be cleaned up by logical decoding machinery.
 */
static void
pgoutput_shutdown(LogicalDecodingContext *ctx)
{
    if (RelationSyncCache)
    {
        hash_destroy(RelationSyncCache);
        RelationSyncCache = NULL;
    }
}

/*
 * Load publications from the list of publication names.
 */
static List *
LoadPublications(List *pubnames)
{
    List       *result = NIL;
    ListCell   *lc;

    foreach(lc, pubnames)
    {
        char       *pubname = (char *) lfirst(lc);
        Publication *pub = GetPublicationByName(pubname, false);

        result = lappend(result, pub);
    }

    return result;
}

/*
 * Publication cache invalidation callback.
 */
static void
publication_invalidation_cb(Datum arg, int cacheid, uint32 hashvalue)
{
    publications_valid = false;

    /*
     * Also invalidate per-relation cache so that next time the filtering info
     * is checked it will be updated with the new publication settings.
     */
    rel_sync_cache_publication_cb(arg, cacheid, hashvalue);
}

/*
 * START STREAM callback
 */
static void
pgoutput_stream_start(struct LogicalDecodingContext *ctx,
                      ReorderBufferTXN *txn)
{
    bool        send_replication_origin = txn->origin_id != InvalidRepOriginId;

    /* we can't nest streaming of transactions */
    Assert(!in_streaming);

    /*
     * If we already sent the first stream for this transaction then don't
     * send the origin id in the subsequent streams.
     */
    if (rbtxn_is_streamed(txn))
        send_replication_origin = false;

    OutputPluginPrepareWrite(ctx, !send_replication_origin);
    logicalrep_write_stream_start(ctx->out, txn->xid, !rbtxn_is_streamed(txn));

    if (send_replication_origin)
    {
        char       *origin;

        /* Message boundary */
        OutputPluginWrite(ctx, false);
        OutputPluginPrepareWrite(ctx, true);

        if (replorigin_by_oid(txn->origin_id, true, &origin))
            logicalrep_write_origin(ctx->out, origin, InvalidXLogRecPtr);
    }

    OutputPluginWrite(ctx, true);

    /* we're streaming a chunk of transaction now */
    in_streaming = true;
}

/*
 * STOP STREAM callback
 */
static void
pgoutput_stream_stop(struct LogicalDecodingContext *ctx,
                     ReorderBufferTXN *txn)
{
    /* we should be streaming a trasanction */
    Assert(in_streaming);

    OutputPluginPrepareWrite(ctx, true);
    logicalrep_write_stream_stop(ctx->out);
    OutputPluginWrite(ctx, true);

    /* we've stopped streaming a transaction */
    in_streaming = false;
}

/*
 * Notify downstream to discard the streamed transaction (along with all
 * it's subtransactions, if it's a toplevel transaction).
 */
static void
pgoutput_stream_abort(struct LogicalDecodingContext *ctx,
                      ReorderBufferTXN *txn,
                      XLogRecPtr abort_lsn)
{
    ReorderBufferTXN *toptxn;

    /*
     * The abort should happen outside streaming block, even for streamed
     * transactions. The transaction has to be marked as streamed, though.
     */
    Assert(!in_streaming);

    /* determine the toplevel transaction */
    toptxn = (txn->toptxn) ? txn->toptxn : txn;

    Assert(rbtxn_is_streamed(toptxn));

    OutputPluginPrepareWrite(ctx, true);
    logicalrep_write_stream_abort(ctx->out, toptxn->xid, txn->xid);
    OutputPluginWrite(ctx, true);

    cleanup_rel_sync_cache(toptxn->xid, false);
}

/*
 * Notify downstream to apply the streamed transaction (along with all
 * it's subtransactions).
 */
static void
pgoutput_stream_commit(struct LogicalDecodingContext *ctx,
                       ReorderBufferTXN *txn,
                       XLogRecPtr commit_lsn)
{
    /*
     * The commit should happen outside streaming block, even for streamed
     * transactions. The transaction has to be marked as streamed, though.
     */
    Assert(!in_streaming);
    Assert(rbtxn_is_streamed(txn));

    OutputPluginUpdateProgress(ctx);

    OutputPluginPrepareWrite(ctx, true);
    logicalrep_write_stream_commit(ctx->out, txn, commit_lsn);
    OutputPluginWrite(ctx, true);

    cleanup_rel_sync_cache(txn->xid, true);
}

/*
 * Initialize the relation schema sync cache for a decoding session.
 *
 * The hash table is destroyed at the end of a decoding session. While
 * relcache invalidations still exist and will still be invoked, they
 * will just see the null hash table global and take no action.
 */
static void
init_rel_sync_cache(MemoryContext cachectx)
{
    HASHCTL     ctl;
    MemoryContext old_ctxt;

    if (RelationSyncCache != NULL)
        return;

    /* Make a new hash table for the cache */
    MemSet(&ctl, 0, sizeof(ctl));
    ctl.keysize = sizeof(Oid);
    ctl.entrysize = sizeof(RelationSyncEntry);
    ctl.hcxt = cachectx;

    old_ctxt = MemoryContextSwitchTo(cachectx);
    RelationSyncCache = hash_create("logical replication output relation cache",
                                    128, &ctl,
                                    HASH_ELEM | HASH_CONTEXT | HASH_BLOBS);
    (void) MemoryContextSwitchTo(old_ctxt);

    Assert(RelationSyncCache != NULL);

    CacheRegisterRelcacheCallback(rel_sync_cache_relation_cb, (Datum) 0);
    CacheRegisterSyscacheCallback(PUBLICATIONRELMAP,
                                  rel_sync_cache_publication_cb,
                                  (Datum) 0);
}

/*
 * We expect relatively small number of streamed transactions.
 */
static bool
get_schema_sent_in_streamed_txn(RelationSyncEntry *entry, TransactionId xid)
{
    ListCell   *lc;

    foreach(lc, entry->streamed_txns)
    {
        if (xid == (uint32) lfirst_int(lc))
            return true;
    }

    return false;
}

/*
 * Add the xid in the rel sync entry for which we have already sent the schema
 * of the relation.
 */
static void
set_schema_sent_in_streamed_txn(RelationSyncEntry *entry, TransactionId xid)
{
    MemoryContext oldctx;

    oldctx = MemoryContextSwitchTo(CacheMemoryContext);

    entry->streamed_txns = lappend_int(entry->streamed_txns, xid);

    MemoryContextSwitchTo(oldctx);
}

/*
 * Find or create entry in the relation schema cache.
 *
 * This looks up publications that the given relation is directly or
 * indirectly part of (the latter if it's really the relation's ancestor that
 * is part of a publication) and fills up the found entry with the information
 * about which operations to publish and whether to use an ancestor's schema
 * when publishing.
 */
static RelationSyncEntry *
get_rel_sync_entry(PGOutputData *data, Oid relid)
{
    RelationSyncEntry *entry;
    bool        am_partition = get_rel_relispartition(relid);
    char        relkind = get_rel_relkind(relid);
    bool        found;
    MemoryContext oldctx;

    Assert(RelationSyncCache != NULL);

    /* Find cached relation info, creating if not found */
    entry = (RelationSyncEntry *) hash_search(RelationSyncCache,
                                              (void *) &relid,
                                              HASH_ENTER, &found);
    Assert(entry != NULL);

    /* Not found means schema wasn't sent */
    if (!found)
    {
        /* immediately make a new entry valid enough to satisfy callbacks */
        entry->schema_sent = false;
        entry->streamed_txns = NIL;
        entry->replicate_valid = false;
        entry->pubactions.pubinsert = entry->pubactions.pubupdate =
            entry->pubactions.pubdelete = entry->pubactions.pubtruncate = false;
        entry->publish_as_relid = InvalidOid;
    }

    /* Validate the entry */
    if (!entry->replicate_valid)
    {
        List       *pubids = GetRelationPublications(relid);
        ListCell   *lc;
        Oid         publish_as_relid = relid;

        /* Reload publications if needed before use. */
        if (!publications_valid)
        {
            oldctx = MemoryContextSwitchTo(CacheMemoryContext);
            if (data->publications)
                list_free_deep(data->publications);

            data->publications = LoadPublications(data->publication_names);
            MemoryContextSwitchTo(oldctx);
            publications_valid = true;
        }

        /*
         * Build publication cache. We can't use one provided by relcache as
         * relcache considers all publications given relation is in, but here
         * we only need to consider ones that the subscriber requested.
         */
        foreach(lc, data->publications)
        {
            Publication *pub = lfirst(lc);
            bool        publish = false;

            if (pub->alltables)
            {
                publish = true;
                if (pub->pubviaroot && am_partition)
                    publish_as_relid = llast_oid(get_partition_ancestors(relid));
            }

            if (!publish)
            {
                bool        ancestor_published = false;

                /*
                 * For a partition, check if any of the ancestors are
                 * published.  If so, note down the topmost ancestor that is
                 * published via this publication, which will be used as the
                 * relation via which to publish the partition's changes.
                 */
                if (am_partition)
                {
                    List       *ancestors = get_partition_ancestors(relid);
                    ListCell   *lc2;

                    /*
                     * Find the "topmost" ancestor that is in this
                     * publication.
                     */
                    foreach(lc2, ancestors)
                    {
                        Oid         ancestor = lfirst_oid(lc2);

                        if (list_member_oid(GetRelationPublications(ancestor),
                                            pub->oid))
                        {
                            ancestor_published = true;
                            if (pub->pubviaroot)
                                publish_as_relid = ancestor;
                        }
                    }
                }

                if (list_member_oid(pubids, pub->oid) || ancestor_published)
                    publish = true;
            }

            /*
             * Don't publish changes for partitioned tables, because
             * publishing those of its partitions suffices, unless partition
             * changes won't be published due to pubviaroot being set.
             */
            if (publish &&
                (relkind != RELKIND_PARTITIONED_TABLE || pub->pubviaroot))
            {
                entry->pubactions.pubinsert |= pub->pubactions.pubinsert;
                entry->pubactions.pubupdate |= pub->pubactions.pubupdate;
                entry->pubactions.pubdelete |= pub->pubactions.pubdelete;
                entry->pubactions.pubtruncate |= pub->pubactions.pubtruncate;
            }

            if (entry->pubactions.pubinsert && entry->pubactions.pubupdate &&
                entry->pubactions.pubdelete && entry->pubactions.pubtruncate)
                break;
        }

        list_free(pubids);

        entry->publish_as_relid = publish_as_relid;
        entry->replicate_valid = true;
    }

    return entry;
}

/*
 * Cleanup list of streamed transactions and update the schema_sent flag.
 *
 * When a streamed transaction commits or aborts, we need to remove the
 * toplevel XID from the schema cache. If the transaction aborted, the
 * subscriber will simply throw away the schema records we streamed, so
 * we don't need to do anything else.
 *
 * If the transaction is committed, the subscriber will update the relation
 * cache - so tweak the schema_sent flag accordingly.
 */
static void
cleanup_rel_sync_cache(TransactionId xid, bool is_commit)
{
    HASH_SEQ_STATUS hash_seq;
    RelationSyncEntry *entry;
    ListCell   *lc;

    Assert(RelationSyncCache != NULL);

    hash_seq_init(&hash_seq, RelationSyncCache);
    while ((entry = hash_seq_search(&hash_seq)) != NULL)
    {
        /*
         * We can set the schema_sent flag for an entry that has committed xid
         * in the list as that ensures that the subscriber would have the
         * corresponding schema and we don't need to send it unless there is
         * any invalidation for that relation.
         */
        foreach(lc, entry->streamed_txns)
        {
            if (xid == (uint32) lfirst_int(lc))
            {
                if (is_commit)
                    entry->schema_sent = true;

                entry->streamed_txns =
                    foreach_delete_current(entry->streamed_txns, lc);
                break;
            }
        }
    }
}

/*
 * Relcache invalidation callback
 */
static void
rel_sync_cache_relation_cb(Datum arg, Oid relid)
{
    RelationSyncEntry *entry;

    /*
     * We can get here if the plugin was used in SQL interface as the
     * RelSchemaSyncCache is destroyed when the decoding finishes, but there
     * is no way to unregister the relcache invalidation callback.
     */
    if (RelationSyncCache == NULL)
        return;

    /*
     * Nobody keeps pointers to entries in this hash table around outside
     * logical decoding callback calls - but invalidation events can come in
     * *during* a callback if we access the relcache in the callback. Because
     * of that we must mark the cache entry as invalid but not remove it from
     * the hash while it could still be referenced, then prune it at a later
     * safe point.
     *
     * Getting invalidations for relations that aren't in the table is
     * entirely normal, since there's no way to unregister for an invalidation
     * event. So we don't care if it's found or not.
     */
    entry = (RelationSyncEntry *) hash_search(RelationSyncCache, &relid,
                                              HASH_FIND, NULL);

    /*
     * Reset schema sent status as the relation definition may have changed.
     */
    if (entry != NULL)
    {
        entry->schema_sent = false;
        list_free(entry->streamed_txns);
        entry->streamed_txns = NIL;
    }
}

/*
 * Publication relation map syscache invalidation callback
 */
static void
rel_sync_cache_publication_cb(Datum arg, int cacheid, uint32 hashvalue)
{
    HASH_SEQ_STATUS status;
    RelationSyncEntry *entry;

    /*
     * We can get here if the plugin was used in SQL interface as the
     * RelSchemaSyncCache is destroyed when the decoding finishes, but there
     * is no way to unregister the relcache invalidation callback.
     */
    if (RelationSyncCache == NULL)
        return;

    /*
     * There is no way to find which entry in our cache the hash belongs to so
     * mark the whole cache as invalid.
     */
    hash_seq_init(&status, RelationSyncCache);
    while ((entry = (RelationSyncEntry *) hash_seq_search(&status)) != NULL)
        entry->replicate_valid = false;
}