partdesc.c

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/*-------------------------------------------------------------------------
 *
 * partdesc.c
 *      Support routines for manipulating partition descriptors
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *        src/backend/partitioning/partdesc.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/genam.h"
#include "access/htup_details.h"
#include "access/table.h"
#include "catalog/partition.h"
#include "catalog/pg_inherits.h"
#include "partitioning/partbounds.h"
#include "partitioning/partdesc.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/hsearch.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/partcache.h"
#include "utils/rel.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
 
typedef struct PartitionDirectoryData
{
    MemoryContext pdir_mcxt;
    HTAB       *pdir_hash;
    bool        omit_detached;
}           PartitionDirectoryData;
 
typedef struct PartitionDirectoryEntry
{
    Oid         reloid;
    Relation    rel;
    PartitionDesc pd;
} PartitionDirectoryEntry;
 
static PartitionDesc RelationBuildPartitionDesc(Relation rel,
                                                bool omit_detached);
 
 
/*
 * RelationGetPartitionDesc -- get partition descriptor, if relation is partitioned
 *
 * We keep two partdescs in relcache: rd_partdesc includes all partitions
 * (even those being concurrently marked detached), while rd_partdesc_nodetached
 * omits (some of) those.  We store the pg_inherits.xmin value for the latter,
 * to determine whether it can be validly reused in each case, since that
 * depends on the active snapshot.
 *
 * Note: we arrange for partition descriptors to not get freed until the
 * relcache entry's refcount goes to zero (see hacks in RelationClose,
 * RelationClearRelation, and RelationBuildPartitionDesc).  Therefore, even
 * though we hand back a direct pointer into the relcache entry, it's safe
 * for callers to continue to use that pointer as long as (a) they hold the
 * relation open, and (b) they hold a relation lock strong enough to ensure
 * that the data doesn't become stale.
 */
PartitionDesc
RelationGetPartitionDesc(Relation rel, bool omit_detached)
{
    Assert(rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
 
    /*
     * If relcache has a partition descriptor, use that.  However, we can only
     * do so when we are asked to include all partitions including detached;
     * and also when we know that there are no detached partitions.
     *
     * If there is no active snapshot, detached partitions aren't omitted
     * either, so we can use the cached descriptor too in that case.
     */
    if (likely(rel->rd_partdesc &&
               (!rel->rd_partdesc->detached_exist || !omit_detached ||
                !ActiveSnapshotSet())))
        return rel->rd_partdesc;
 
    /*
     * If we're asked to omit detached partitions, we may be able to use a
     * cached descriptor too.  We determine that based on the pg_inherits.xmin
     * that was saved alongside that descriptor: if the xmin that was not in
     * progress for that active snapshot is also not in progress for the
     * current active snapshot, then we can use it.  Otherwise build one from
     * scratch.
     */
    if (omit_detached &&
        rel->rd_partdesc_nodetached &&
        ActiveSnapshotSet())
    {
        Snapshot    activesnap;
 
        Assert(TransactionIdIsValid(rel->rd_partdesc_nodetached_xmin));
        activesnap = GetActiveSnapshot();
 
        if (!XidInMVCCSnapshot(rel->rd_partdesc_nodetached_xmin, activesnap))
            return rel->rd_partdesc_nodetached;
    }
 
    return RelationBuildPartitionDesc(rel, omit_detached);
}
 
/*
 * RelationBuildPartitionDesc
 *      Form rel's partition descriptor, and store in relcache entry
 *
 * Partition descriptor is a complex structure; to avoid complicated logic to
 * free individual elements whenever the relcache entry is flushed, we give it
 * its own memory context, a child of CacheMemoryContext, which can easily be
 * deleted on its own.  To avoid leaking memory in that context in case of an
 * error partway through this function, the context is initially created as a
 * child of CurTransactionContext and only re-parented to CacheMemoryContext
 * at the end, when no further errors are possible.  Also, we don't make this
 * context the current context except in very brief code sections, out of fear
 * that some of our callees allocate memory on their own which would be leaked
 * permanently.
 *
 * As a special case, partition descriptors that are requested to omit
 * partitions being detached (and which contain such partitions) are transient
 * and are not associated with the relcache entry.  Such descriptors only last
 * through the requesting Portal, so we use the corresponding memory context
 * for them.
 */
static PartitionDesc
RelationBuildPartitionDesc(Relation rel, bool omit_detached)
{
    PartitionDesc partdesc;
    PartitionBoundInfo boundinfo = NULL;
    List       *inhoids;
    PartitionBoundSpec **boundspecs = NULL;
    Oid        *oids = NULL;
    bool       *is_leaf = NULL;
    bool        detached_exist;
    bool        is_omit;
    TransactionId detached_xmin;
    ListCell   *cell;
    int         i,
                nparts;
    bool        retried = false;
    PartitionKey key = RelationGetPartitionKey(rel);
    MemoryContext new_pdcxt;
    MemoryContext oldcxt;
    int        *mapping;
 
retry:
 
    /*
     * Get partition oids from pg_inherits.  This uses a single snapshot to
     * fetch the list of children, so while more children may be getting added
     * or removed concurrently, whatever this function returns will be
     * accurate as of some well-defined point in time.
     */
    detached_exist = false;
    detached_xmin = InvalidTransactionId;
    inhoids = find_inheritance_children_extended(RelationGetRelid(rel),
                                                 omit_detached, NoLock,
                                                 &detached_exist,
                                                 &detached_xmin);
 
    nparts = list_length(inhoids);
 
    /* Allocate working arrays for OIDs, leaf flags, and boundspecs. */
    if (nparts > 0)
    {
        oids = (Oid *) palloc(nparts * sizeof(Oid));
        is_leaf = (bool *) palloc(nparts * sizeof(bool));
        boundspecs = palloc(nparts * sizeof(PartitionBoundSpec *));
    }
 
    /* Collect bound spec nodes for each partition. */
    i = 0;
    foreach(cell, inhoids)
    {
        Oid         inhrelid = lfirst_oid(cell);
        HeapTuple   tuple;
        PartitionBoundSpec *boundspec = NULL;
 
        /* Try fetching the tuple from the catcache, for speed. */
        tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(inhrelid));
        if (HeapTupleIsValid(tuple))
        {
            Datum       datum;
            bool        isnull;
 
            datum = SysCacheGetAttr(RELOID, tuple,
                                    Anum_pg_class_relpartbound,
                                    &isnull);
            if (!isnull)
                boundspec = stringToNode(TextDatumGetCString(datum));
            ReleaseSysCache(tuple);
        }
 
        /*
         * Two problems are possible here.  First, a concurrent ATTACH
         * PARTITION might be in the process of adding a new partition, but
         * the syscache doesn't have it, or its copy of it does not yet have
         * its relpartbound set.  We cannot just AcceptInvalidationMessages(),
         * because the other process might have already removed itself from
         * the ProcArray but not yet added its invalidation messages to the
         * shared queue.  We solve this problem by reading pg_class directly
         * for the desired tuple.
         *
         * If the partition recently detached is also dropped, we get no tuple
         * from the scan.  In that case, we also retry, and next time through
         * here, we don't see that partition anymore.
         *
         * The other problem is that DETACH CONCURRENTLY is in the process of
         * removing a partition, which happens in two steps: first it marks it
         * as "detach pending", commits, then unsets relpartbound.  If
         * find_inheritance_children_extended included that partition but we
         * below we see that DETACH CONCURRENTLY has reset relpartbound for
         * it, we'd see an inconsistent view.  (The inconsistency is seen
         * because table_open below reads invalidation messages.)  We protect
         * against this by retrying find_inheritance_children_extended().
         */
        if (boundspec == NULL)
        {
            Relation    pg_class;
            SysScanDesc scan;
            ScanKeyData key[1];
 
            pg_class = table_open(RelationRelationId, AccessShareLock);
            ScanKeyInit(&key[0],
                        Anum_pg_class_oid,
                        BTEqualStrategyNumber, F_OIDEQ,
                        ObjectIdGetDatum(inhrelid));
            scan = systable_beginscan(pg_class, ClassOidIndexId, true,
                                      NULL, 1, key);
 
            /*
             * We could get one tuple from the scan (the normal case), or zero
             * tuples if the table has been dropped meanwhile.
             */
            tuple = systable_getnext(scan);
            if (HeapTupleIsValid(tuple))
            {
                Datum       datum;
                bool        isnull;
 
                datum = heap_getattr(tuple, Anum_pg_class_relpartbound,
                                     RelationGetDescr(pg_class), &isnull);
                if (!isnull)
                    boundspec = stringToNode(TextDatumGetCString(datum));
            }
            systable_endscan(scan);
            table_close(pg_class, AccessShareLock);
 
            /*
             * If we still don't get a relpartbound value (either because
             * boundspec is null or because there was no tuple), then it must
             * be because of DETACH CONCURRENTLY.  Restart from the top, as
             * explained above.  We only do this once, for two reasons: first,
             * only one DETACH CONCURRENTLY session could affect us at a time,
             * since each of them would have to wait for the snapshot under
             * which this is running; and second, to avoid possible infinite
             * loops in case of catalog corruption.
             *
             * Note that the current memory context is short-lived enough, so
             * we needn't worry about memory leaks here.
             */
            if (!boundspec && !retried)
            {
                AcceptInvalidationMessages();
                retried = true;
                goto retry;
            }
        }
 
        /* Sanity checks. */
        if (!boundspec)
            elog(ERROR, "missing relpartbound for relation %u", inhrelid);
        if (!IsA(boundspec, PartitionBoundSpec))
            elog(ERROR, "invalid relpartbound for relation %u", inhrelid);
 
        /*
         * If the PartitionBoundSpec says this is the default partition, its
         * OID should match pg_partitioned_table.partdefid; if not, the
         * catalog is corrupt.
         */
        if (boundspec->is_default)
        {
            Oid         partdefid;
 
            partdefid = get_default_partition_oid(RelationGetRelid(rel));
            if (partdefid != inhrelid)
                elog(ERROR, "expected partdefid %u, but got %u",
                     inhrelid, partdefid);
        }
 
        /* Save results. */
        oids[i] = inhrelid;
        is_leaf[i] = (get_rel_relkind(inhrelid) != RELKIND_PARTITIONED_TABLE);
        boundspecs[i] = boundspec;
        ++i;
    }
 
    /*
     * Create PartitionBoundInfo and mapping, working in the caller's context.
     * This could fail, but we haven't done any damage if so.
     */
    if (nparts > 0)
        boundinfo = partition_bounds_create(boundspecs, nparts, key, &mapping);
 
    /*
     * Now build the actual relcache partition descriptor, copying all the
     * data into a new, small context.  As per above comment, we don't make
     * this a long-lived context until it's finished.
     */
    new_pdcxt = AllocSetContextCreate(CurTransactionContext,
                                      "partition descriptor",
                                      ALLOCSET_SMALL_SIZES);
    MemoryContextCopyAndSetIdentifier(new_pdcxt,
                                      RelationGetRelationName(rel));
 
    partdesc = (PartitionDescData *)
        MemoryContextAllocZero(new_pdcxt, sizeof(PartitionDescData));
    partdesc->nparts = nparts;
    partdesc->detached_exist = detached_exist;
    /* If there are no partitions, the rest of the partdesc can stay zero */
    if (nparts > 0)
    {
        oldcxt = MemoryContextSwitchTo(new_pdcxt);
        partdesc->boundinfo = partition_bounds_copy(boundinfo, key);
 
        /* Initialize caching fields for speeding up ExecFindPartition */
        partdesc->last_found_datum_index = -1;
        partdesc->last_found_part_index = -1;
        partdesc->last_found_count = 0;
 
        partdesc->oids = (Oid *) palloc(nparts * sizeof(Oid));
        partdesc->is_leaf = (bool *) palloc(nparts * sizeof(bool));
 
        /*
         * Assign OIDs from the original array into mapped indexes of the
         * result array.  The order of OIDs in the former is defined by the
         * catalog scan that retrieved them, whereas that in the latter is
         * defined by canonicalized representation of the partition bounds.
         * Also save leaf-ness of each partition.
         */
        for (i = 0; i < nparts; i++)
        {
            int         index = mapping[i];
 
            partdesc->oids[index] = oids[i];
            partdesc->is_leaf[index] = is_leaf[i];
        }
        MemoryContextSwitchTo(oldcxt);
    }
 
    /*
     * Are we working with the partdesc that omits the detached partition, or
     * the one that includes it?
     *
     * Note that if a partition was found by the catalog's scan to have been
     * detached, but the pg_inherit tuple saying so was not visible to the
     * active snapshot (find_inheritance_children_extended will not have set
     * detached_xmin in that case), we consider there to be no "omittable"
     * detached partitions.
     */
    is_omit = omit_detached && detached_exist && ActiveSnapshotSet() &&
        TransactionIdIsValid(detached_xmin);
 
    /*
     * We have a fully valid partdesc.  Reparent it so that it has the right
     * lifespan.
     */
    MemoryContextSetParent(new_pdcxt, CacheMemoryContext);
 
    /*
     * Store it into relcache.
     *
     * But first, a kluge: if there's an old context for this type of
     * descriptor, it contains an old partition descriptor that may still be
     * referenced somewhere.  Preserve it, while not leaking it, by
     * reattaching it as a child context of the new one.  Eventually it will
     * get dropped by either RelationClose or RelationClearRelation. (We keep
     * the regular partdesc in rd_pdcxt, and the partdesc-excluding-
     * detached-partitions in rd_pddcxt.)
     */
    if (is_omit)
    {
        if (rel->rd_pddcxt != NULL)
            MemoryContextSetParent(rel->rd_pddcxt, new_pdcxt);
        rel->rd_pddcxt = new_pdcxt;
        rel->rd_partdesc_nodetached = partdesc;
 
        /*
         * For partdescs built excluding detached partitions, which we save
         * separately, we also record the pg_inherits.xmin of the detached
         * partition that was omitted; this informs a future potential user of
         * such a cached partdesc to only use it after cross-checking that the
         * xmin is indeed visible to the snapshot it is going to be working
         * with.
         */
        Assert(TransactionIdIsValid(detached_xmin));
        rel->rd_partdesc_nodetached_xmin = detached_xmin;
    }
    else
    {
        if (rel->rd_pdcxt != NULL)
            MemoryContextSetParent(rel->rd_pdcxt, new_pdcxt);
        rel->rd_pdcxt = new_pdcxt;
        rel->rd_partdesc = partdesc;
    }
 
    return partdesc;
}
 
/*
 * CreatePartitionDirectory
 *      Create a new partition directory object.
 */
PartitionDirectory
CreatePartitionDirectory(MemoryContext mcxt, bool omit_detached)
{
    MemoryContext oldcontext = MemoryContextSwitchTo(mcxt);
    PartitionDirectory pdir;
    HASHCTL     ctl;
 
    pdir = palloc(sizeof(PartitionDirectoryData));
    pdir->pdir_mcxt = mcxt;
 
    ctl.keysize = sizeof(Oid);
    ctl.entrysize = sizeof(PartitionDirectoryEntry);
    ctl.hcxt = mcxt;
 
    pdir->pdir_hash = hash_create("partition directory", 256, &ctl,
                                  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
    pdir->omit_detached = omit_detached;
 
    MemoryContextSwitchTo(oldcontext);
    return pdir;
}
 
/*
 * PartitionDirectoryLookup
 *      Look up the partition descriptor for a relation in the directory.
 *
 * The purpose of this function is to ensure that we get the same
 * PartitionDesc for each relation every time we look it up.  In the
 * face of concurrent DDL, different PartitionDescs may be constructed with
 * different views of the catalog state, but any single particular OID
 * will always get the same PartitionDesc for as long as the same
 * PartitionDirectory is used.
 */
PartitionDesc
PartitionDirectoryLookup(PartitionDirectory pdir, Relation rel)
{
    PartitionDirectoryEntry *pde;
    Oid         relid = RelationGetRelid(rel);
    bool        found;
 
    pde = hash_search(pdir->pdir_hash, &relid, HASH_ENTER, &found);
    if (!found)
    {
        /*
         * We must keep a reference count on the relation so that the
         * PartitionDesc to which we are pointing can't get destroyed.
         */
        RelationIncrementReferenceCount(rel);
        pde->rel = rel;
        pde->pd = RelationGetPartitionDesc(rel, pdir->omit_detached);
        Assert(pde->pd != NULL);
    }
    return pde->pd;
}
 
/*
 * DestroyPartitionDirectory
 *      Destroy a partition directory.
 *
 * Release the reference counts we're holding.
 */
void
DestroyPartitionDirectory(PartitionDirectory pdir)
{
    HASH_SEQ_STATUS status;
    PartitionDirectoryEntry *pde;
 
    hash_seq_init(&status, pdir->pdir_hash);
    while ((pde = hash_seq_search(&status)) != NULL)
        RelationDecrementReferenceCount(pde->rel);
}
 
/*
 * get_default_oid_from_partdesc
 *
 * Given a partition descriptor, return the OID of the default partition, if
 * one exists; else, return InvalidOid.
 */
Oid
get_default_oid_from_partdesc(PartitionDesc partdesc)
{
    if (partdesc && partdesc->boundinfo &&
        partition_bound_has_default(partdesc->boundinfo))
        return partdesc->oids[partdesc->boundinfo->default_index];
 
    return InvalidOid;
}