cluster.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * cluster.c
 *    CLUSTER a table on an index.  This is now also used for VACUUM FULL.
 *
 * There is hardly anything left of Paul Brown's original implementation...
 *
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994-5, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/cluster.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/amapi.h"
#include "access/heapam.h"
#include "access/multixact.h"
#include "access/relscan.h"
#include "access/tableam.h"
#include "access/toast_internals.h"
#include "access/transam.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/heap.h"
#include "catalog/index.h"
#include "catalog/namespace.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_am.h"
#include "catalog/toasting.h"
#include "commands/cluster.h"
#include "commands/progress.h"
#include "commands/tablecmds.h"
#include "commands/vacuum.h"
#include "miscadmin.h"
#include "optimizer/optimizer.h"
#include "pgstat.h"
#include "storage/bufmgr.h"
#include "storage/lmgr.h"
#include "storage/predicate.h"
#include "utils/acl.h"
#include "utils/fmgroids.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/pg_rusage.h"
#include "utils/relmapper.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
#include "utils/tuplesort.h"

/*
 * This struct is used to pass around the information on tables to be
 * clustered. We need this so we can make a list of them when invoked without
 * a specific table/index pair.
 */
typedef struct
{
    Oid         tableOid;
    Oid         indexOid;
} RelToCluster;


static void rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose);
static void copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex,
                            bool verbose, bool *pSwapToastByContent,
                            TransactionId *pFreezeXid, MultiXactId *pCutoffMulti);
static List *get_tables_to_cluster(MemoryContext cluster_context);


/*---------------------------------------------------------------------------
 * This cluster code allows for clustering multiple tables at once. Because
 * of this, we cannot just run everything on a single transaction, or we
 * would be forced to acquire exclusive locks on all the tables being
 * clustered, simultaneously --- very likely leading to deadlock.
 *
 * To solve this we follow a similar strategy to VACUUM code,
 * clustering each relation in a separate transaction. For this to work,
 * we need to:
 *  - provide a separate memory context so that we can pass information in
 *    a way that survives across transactions
 *  - start a new transaction every time a new relation is clustered
 *  - check for validity of the information on to-be-clustered relations,
 *    as someone might have deleted a relation behind our back, or
 *    clustered one on a different index
 *  - end the transaction
 *
 * The single-relation case does not have any such overhead.
 *
 * We also allow a relation to be specified without index.  In that case,
 * the indisclustered bit will be looked up, and an ERROR will be thrown
 * if there is no index with the bit set.
 *---------------------------------------------------------------------------
 */
void
cluster(ClusterStmt *stmt, bool isTopLevel)
{
    if (stmt->relation != NULL)
    {
        /* This is the single-relation case. */
        Oid         tableOid,
                    indexOid = InvalidOid;
        Relation    rel;

        /* Find, lock, and check permissions on the table */
        tableOid = RangeVarGetRelidExtended(stmt->relation,
                                            AccessExclusiveLock,
                                            0,
                                            RangeVarCallbackOwnsTable, NULL);
        rel = table_open(tableOid, NoLock);

        /*
         * Reject clustering a remote temp table ... their local buffer
         * manager is not going to cope.
         */
        if (RELATION_IS_OTHER_TEMP(rel))
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("cannot cluster temporary tables of other sessions")));

        /*
         * Reject clustering a partitioned table.
         */
        if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("cannot cluster a partitioned table")));

        if (stmt->indexname == NULL)
        {
            ListCell   *index;

            /* We need to find the index that has indisclustered set. */
            foreach(index, RelationGetIndexList(rel))
            {
                HeapTuple   idxtuple;
                Form_pg_index indexForm;

                indexOid = lfirst_oid(index);
                idxtuple = SearchSysCache1(INDEXRELID,
                                           ObjectIdGetDatum(indexOid));
                if (!HeapTupleIsValid(idxtuple))
                    elog(ERROR, "cache lookup failed for index %u", indexOid);
                indexForm = (Form_pg_index) GETSTRUCT(idxtuple);
                if (indexForm->indisclustered)
                {
                    ReleaseSysCache(idxtuple);
                    break;
                }
                ReleaseSysCache(idxtuple);
                indexOid = InvalidOid;
            }

            if (!OidIsValid(indexOid))
                ereport(ERROR,
                        (errcode(ERRCODE_UNDEFINED_OBJECT),
                         errmsg("there is no previously clustered index for table \"%s\"",
                                stmt->relation->relname)));
        }
        else
        {
            /*
             * The index is expected to be in the same namespace as the
             * relation.
             */
            indexOid = get_relname_relid(stmt->indexname,
                                         rel->rd_rel->relnamespace);
            if (!OidIsValid(indexOid))
                ereport(ERROR,
                        (errcode(ERRCODE_UNDEFINED_OBJECT),
                         errmsg("index \"%s\" for table \"%s\" does not exist",
                                stmt->indexname, stmt->relation->relname)));
        }

        /* close relation, keep lock till commit */
        table_close(rel, NoLock);

        /* Do the job. */
        cluster_rel(tableOid, indexOid, stmt->options);
    }
    else
    {
        /*
         * This is the "multi relation" case. We need to cluster all tables
         * that have some index with indisclustered set.
         */
        MemoryContext cluster_context;
        List       *rvs;
        ListCell   *rv;

        /*
         * We cannot run this form of CLUSTER inside a user transaction block;
         * we'd be holding locks way too long.
         */
        PreventInTransactionBlock(isTopLevel, "CLUSTER");

        /*
         * Create special memory context for cross-transaction storage.
         *
         * Since it is a child of PortalContext, it will go away even in case
         * of error.
         */
        cluster_context = AllocSetContextCreate(PortalContext,
                                                "Cluster",
                                                ALLOCSET_DEFAULT_SIZES);

        /*
         * Build the list of relations to cluster.  Note that this lives in
         * cluster_context.
         */
        rvs = get_tables_to_cluster(cluster_context);

        /* Commit to get out of starting transaction */
        PopActiveSnapshot();
        CommitTransactionCommand();

        /* Ok, now that we've got them all, cluster them one by one */
        foreach(rv, rvs)
        {
            RelToCluster *rvtc = (RelToCluster *) lfirst(rv);

            /* Start a new transaction for each relation. */
            StartTransactionCommand();
            /* functions in indexes may want a snapshot set */
            PushActiveSnapshot(GetTransactionSnapshot());
            /* Do the job. */
            cluster_rel(rvtc->tableOid, rvtc->indexOid,
                        stmt->options | CLUOPT_RECHECK);
            PopActiveSnapshot();
            CommitTransactionCommand();
        }

        /* Start a new transaction for the cleanup work. */
        StartTransactionCommand();

        /* Clean up working storage */
        MemoryContextDelete(cluster_context);
    }
}

/*
 * cluster_rel
 *
 * This clusters the table by creating a new, clustered table and
 * swapping the relfilenodes of the new table and the old table, so
 * the OID of the original table is preserved.  Thus we do not lose
 * GRANT, inheritance nor references to this table (this was a bug
 * in releases through 7.3).
 *
 * Indexes are rebuilt too, via REINDEX. Since we are effectively bulk-loading
 * the new table, it's better to create the indexes afterwards than to fill
 * them incrementally while we load the table.
 *
 * If indexOid is InvalidOid, the table will be rewritten in physical order
 * instead of index order.  This is the new implementation of VACUUM FULL,
 * and error messages should refer to the operation as VACUUM not CLUSTER.
 */
void
cluster_rel(Oid tableOid, Oid indexOid, int options)
{
    Relation    OldHeap;
    bool        verbose = ((options & CLUOPT_VERBOSE) != 0);
    bool        recheck = ((options & CLUOPT_RECHECK) != 0);

    /* Check for user-requested abort. */
    CHECK_FOR_INTERRUPTS();

    pgstat_progress_start_command(PROGRESS_COMMAND_CLUSTER, tableOid);
    if (OidIsValid(indexOid))
        pgstat_progress_update_param(PROGRESS_CLUSTER_COMMAND,
                                     PROGRESS_CLUSTER_COMMAND_CLUSTER);
    else
        pgstat_progress_update_param(PROGRESS_CLUSTER_COMMAND,
                                     PROGRESS_CLUSTER_COMMAND_VACUUM_FULL);

    /*
     * We grab exclusive access to the target rel and index for the duration
     * of the transaction.  (This is redundant for the single-transaction
     * case, since cluster() already did it.)  The index lock is taken inside
     * check_index_is_clusterable.
     */
    OldHeap = try_relation_open(tableOid, AccessExclusiveLock);

    /* If the table has gone away, we can skip processing it */
    if (!OldHeap)
    {
        pgstat_progress_end_command();
        return;
    }

    /*
     * Since we may open a new transaction for each relation, we have to check
     * that the relation still is what we think it is.
     *
     * If this is a single-transaction CLUSTER, we can skip these tests. We
     * *must* skip the one on indisclustered since it would reject an attempt
     * to cluster a not-previously-clustered index.
     */
    if (recheck)
    {
        HeapTuple   tuple;
        Form_pg_index indexForm;

        /* Check that the user still owns the relation */
        if (!pg_class_ownercheck(tableOid, GetUserId()))
        {
            relation_close(OldHeap, AccessExclusiveLock);
            pgstat_progress_end_command();
            return;
        }

        /*
         * Silently skip a temp table for a remote session.  Only doing this
         * check in the "recheck" case is appropriate (which currently means
         * somebody is executing a database-wide CLUSTER), because there is
         * another check in cluster() which will stop any attempt to cluster
         * remote temp tables by name.  There is another check in cluster_rel
         * which is redundant, but we leave it for extra safety.
         */
        if (RELATION_IS_OTHER_TEMP(OldHeap))
        {
            relation_close(OldHeap, AccessExclusiveLock);
            pgstat_progress_end_command();
            return;
        }

        if (OidIsValid(indexOid))
        {
            /*
             * Check that the index still exists
             */
            if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(indexOid)))
            {
                relation_close(OldHeap, AccessExclusiveLock);
                pgstat_progress_end_command();
                return;
            }

            /*
             * Check that the index is still the one with indisclustered set.
             */
            tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(indexOid));
            if (!HeapTupleIsValid(tuple))   /* probably can't happen */
            {
                relation_close(OldHeap, AccessExclusiveLock);
                pgstat_progress_end_command();
                return;
            }
            indexForm = (Form_pg_index) GETSTRUCT(tuple);
            if (!indexForm->indisclustered)
            {
                ReleaseSysCache(tuple);
                relation_close(OldHeap, AccessExclusiveLock);
                pgstat_progress_end_command();
                return;
            }
            ReleaseSysCache(tuple);
        }
    }

    /*
     * We allow VACUUM FULL, but not CLUSTER, on shared catalogs.  CLUSTER
     * would work in most respects, but the index would only get marked as
     * indisclustered in the current database, leading to unexpected behavior
     * if CLUSTER were later invoked in another database.
     */
    if (OidIsValid(indexOid) && OldHeap->rd_rel->relisshared)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot cluster a shared catalog")));

    /*
     * Don't process temp tables of other backends ... their local buffer
     * manager is not going to cope.
     */
    if (RELATION_IS_OTHER_TEMP(OldHeap))
    {
        if (OidIsValid(indexOid))
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("cannot cluster temporary tables of other sessions")));
        else
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("cannot vacuum temporary tables of other sessions")));
    }

    /*
     * Also check for active uses of the relation in the current transaction,
     * including open scans and pending AFTER trigger events.
     */
    CheckTableNotInUse(OldHeap, OidIsValid(indexOid) ? "CLUSTER" : "VACUUM");

    /* Check heap and index are valid to cluster on */
    if (OidIsValid(indexOid))
        check_index_is_clusterable(OldHeap, indexOid, recheck, AccessExclusiveLock);

    /*
     * Quietly ignore the request if this is a materialized view which has not
     * been populated from its query. No harm is done because there is no data
     * to deal with, and we don't want to throw an error if this is part of a
     * multi-relation request -- for example, CLUSTER was run on the entire
     * database.
     */
    if (OldHeap->rd_rel->relkind == RELKIND_MATVIEW &&
        !RelationIsPopulated(OldHeap))
    {
        relation_close(OldHeap, AccessExclusiveLock);
        pgstat_progress_end_command();
        return;
    }

    /*
     * All predicate locks on the tuples or pages are about to be made
     * invalid, because we move tuples around.  Promote them to relation
     * locks.  Predicate locks on indexes will be promoted when they are
     * reindexed.
     */
    TransferPredicateLocksToHeapRelation(OldHeap);

    /* rebuild_relation does all the dirty work */
    rebuild_relation(OldHeap, indexOid, verbose);

    /* NB: rebuild_relation does table_close() on OldHeap */

    pgstat_progress_end_command();
}

/*
 * Verify that the specified heap and index are valid to cluster on
 *
 * Side effect: obtains lock on the index.  The caller may
 * in some cases already have AccessExclusiveLock on the table, but
 * not in all cases so we can't rely on the table-level lock for
 * protection here.
 */
void
check_index_is_clusterable(Relation OldHeap, Oid indexOid, bool recheck, LOCKMODE lockmode)
{
    Relation    OldIndex;

    OldIndex = index_open(indexOid, lockmode);

    /*
     * Check that index is in fact an index on the given relation
     */
    if (OldIndex->rd_index == NULL ||
        OldIndex->rd_index->indrelid != RelationGetRelid(OldHeap))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not an index for table \"%s\"",
                        RelationGetRelationName(OldIndex),
                        RelationGetRelationName(OldHeap))));

    /* Index AM must allow clustering */
    if (!OldIndex->rd_indam->amclusterable)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot cluster on index \"%s\" because access method does not support clustering",
                        RelationGetRelationName(OldIndex))));

    /*
     * Disallow clustering on incomplete indexes (those that might not index
     * every row of the relation).  We could relax this by making a separate
     * seqscan pass over the table to copy the missing rows, but that seems
     * expensive and tedious.
     */
    if (!heap_attisnull(OldIndex->rd_indextuple, Anum_pg_index_indpred, NULL))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot cluster on partial index \"%s\"",
                        RelationGetRelationName(OldIndex))));

    /*
     * Disallow if index is left over from a failed CREATE INDEX CONCURRENTLY;
     * it might well not contain entries for every heap row, or might not even
     * be internally consistent.  (But note that we don't check indcheckxmin;
     * the worst consequence of following broken HOT chains would be that we
     * might put recently-dead tuples out-of-order in the new table, and there
     * is little harm in that.)
     */
    if (!OldIndex->rd_index->indisvalid)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot cluster on invalid index \"%s\"",
                        RelationGetRelationName(OldIndex))));

    /* Drop relcache refcnt on OldIndex, but keep lock */
    index_close(OldIndex, NoLock);
}

/*
 * mark_index_clustered: mark the specified index as the one clustered on
 *
 * With indexOid == InvalidOid, will mark all indexes of rel not-clustered.
 */
void
mark_index_clustered(Relation rel, Oid indexOid, bool is_internal)
{
    HeapTuple   indexTuple;
    Form_pg_index indexForm;
    Relation    pg_index;
    ListCell   *index;

    /* Disallow applying to a partitioned table */
    if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot mark index clustered in partitioned table")));

    /*
     * If the index is already marked clustered, no need to do anything.
     */
    if (OidIsValid(indexOid))
    {
        indexTuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(indexOid));
        if (!HeapTupleIsValid(indexTuple))
            elog(ERROR, "cache lookup failed for index %u", indexOid);
        indexForm = (Form_pg_index) GETSTRUCT(indexTuple);

        if (indexForm->indisclustered)
        {
            ReleaseSysCache(indexTuple);
            return;
        }

        ReleaseSysCache(indexTuple);
    }

    /*
     * Check each index of the relation and set/clear the bit as needed.
     */
    pg_index = table_open(IndexRelationId, RowExclusiveLock);

    foreach(index, RelationGetIndexList(rel))
    {
        Oid         thisIndexOid = lfirst_oid(index);

        indexTuple = SearchSysCacheCopy1(INDEXRELID,
                                         ObjectIdGetDatum(thisIndexOid));
        if (!HeapTupleIsValid(indexTuple))
            elog(ERROR, "cache lookup failed for index %u", thisIndexOid);
        indexForm = (Form_pg_index) GETSTRUCT(indexTuple);

        /*
         * Unset the bit if set.  We know it's wrong because we checked this
         * earlier.
         */
        if (indexForm->indisclustered)
        {
            indexForm->indisclustered = false;
            CatalogTupleUpdate(pg_index, &indexTuple->t_self, indexTuple);
        }
        else if (thisIndexOid == indexOid)
        {
            /* this was checked earlier, but let's be real sure */
            if (!indexForm->indisvalid)
                elog(ERROR, "cannot cluster on invalid index %u", indexOid);
            indexForm->indisclustered = true;
            CatalogTupleUpdate(pg_index, &indexTuple->t_self, indexTuple);
        }

        InvokeObjectPostAlterHookArg(IndexRelationId, thisIndexOid, 0,
                                     InvalidOid, is_internal);

        heap_freetuple(indexTuple);
    }

    table_close(pg_index, RowExclusiveLock);
}

/*
 * rebuild_relation: rebuild an existing relation in index or physical order
 *
 * OldHeap: table to rebuild --- must be opened and exclusive-locked!
 * indexOid: index to cluster by, or InvalidOid to rewrite in physical order.
 *
 * NB: this routine closes OldHeap at the right time; caller should not.
 */
static void
rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose)
{
    Oid         tableOid = RelationGetRelid(OldHeap);
    Oid         tableSpace = OldHeap->rd_rel->reltablespace;
    Oid         OIDNewHeap;
    char        relpersistence;
    bool        is_system_catalog;
    bool        swap_toast_by_content;
    TransactionId frozenXid;
    MultiXactId cutoffMulti;

    /* Mark the correct index as clustered */
    if (OidIsValid(indexOid))
        mark_index_clustered(OldHeap, indexOid, true);

    /* Remember info about rel before closing OldHeap */
    relpersistence = OldHeap->rd_rel->relpersistence;
    is_system_catalog = IsSystemRelation(OldHeap);

    /* Close relcache entry, but keep lock until transaction commit */
    table_close(OldHeap, NoLock);

    /* Create the transient table that will receive the re-ordered data */
    OIDNewHeap = make_new_heap(tableOid, tableSpace,
                               relpersistence,
                               AccessExclusiveLock);

    /* Copy the heap data into the new table in the desired order */
    copy_table_data(OIDNewHeap, tableOid, indexOid, verbose,
                    &swap_toast_by_content, &frozenXid, &cutoffMulti);

    /*
     * Swap the physical files of the target and transient tables, then
     * rebuild the target's indexes and throw away the transient table.
     */
    finish_heap_swap(tableOid, OIDNewHeap, is_system_catalog,
                     swap_toast_by_content, false, true,
                     frozenXid, cutoffMulti,
                     relpersistence);
}


/*
 * Create the transient table that will be filled with new data during
 * CLUSTER, ALTER TABLE, and similar operations.  The transient table
 * duplicates the logical structure of the OldHeap, but is placed in
 * NewTableSpace which might be different from OldHeap's.  Also, it's built
 * with the specified persistence, which might differ from the original's.
 *
 * After this, the caller should load the new heap with transferred/modified
 * data, then call finish_heap_swap to complete the operation.
 */
Oid
make_new_heap(Oid OIDOldHeap, Oid NewTableSpace, char relpersistence,
              LOCKMODE lockmode)
{
    TupleDesc   OldHeapDesc;
    char        NewHeapName[NAMEDATALEN];
    Oid         OIDNewHeap;
    Oid         toastid;
    Relation    OldHeap;
    HeapTuple   tuple;
    Datum       reloptions;
    bool        isNull;
    Oid         namespaceid;

    OldHeap = table_open(OIDOldHeap, lockmode);
    OldHeapDesc = RelationGetDescr(OldHeap);

    /*
     * Note that the NewHeap will not receive any of the defaults or
     * constraints associated with the OldHeap; we don't need 'em, and there's
     * no reason to spend cycles inserting them into the catalogs only to
     * delete them.
     */

    /*
     * But we do want to use reloptions of the old heap for new heap.
     */
    tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(OIDOldHeap));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for relation %u", OIDOldHeap);
    reloptions = SysCacheGetAttr(RELOID, tuple, Anum_pg_class_reloptions,
                                 &isNull);
    if (isNull)
        reloptions = (Datum) 0;

    if (relpersistence == RELPERSISTENCE_TEMP)
        namespaceid = LookupCreationNamespace("pg_temp");
    else
        namespaceid = RelationGetNamespace(OldHeap);

    /*
     * Create the new heap, using a temporary name in the same namespace as
     * the existing table.  NOTE: there is some risk of collision with user
     * relnames.  Working around this seems more trouble than it's worth; in
     * particular, we can't create the new heap in a different namespace from
     * the old, or we will have problems with the TEMP status of temp tables.
     *
     * Note: the new heap is not a shared relation, even if we are rebuilding
     * a shared rel.  However, we do make the new heap mapped if the source is
     * mapped.  This simplifies swap_relation_files, and is absolutely
     * necessary for rebuilding pg_class, for reasons explained there.
     */
    snprintf(NewHeapName, sizeof(NewHeapName), "pg_temp_%u", OIDOldHeap);

    OIDNewHeap = heap_create_with_catalog(NewHeapName,
                                          namespaceid,
                                          NewTableSpace,
                                          InvalidOid,
                                          InvalidOid,
                                          InvalidOid,
                                          OldHeap->rd_rel->relowner,
                                          OldHeap->rd_rel->relam,
                                          OldHeapDesc,
                                          NIL,
                                          RELKIND_RELATION,
                                          relpersistence,
                                          false,
                                          RelationIsMapped(OldHeap),
                                          ONCOMMIT_NOOP,
                                          reloptions,
                                          false,
                                          true,
                                          true,
                                          OIDOldHeap,
                                          NULL);
    Assert(OIDNewHeap != InvalidOid);

    ReleaseSysCache(tuple);

    /*
     * Advance command counter so that the newly-created relation's catalog
     * tuples will be visible to table_open.
     */
    CommandCounterIncrement();

    /*
     * If necessary, create a TOAST table for the new relation.
     *
     * If the relation doesn't have a TOAST table already, we can't need one
     * for the new relation.  The other way around is possible though: if some
     * wide columns have been dropped, NewHeapCreateToastTable can decide that
     * no TOAST table is needed for the new table.
     *
     * Note that NewHeapCreateToastTable ends with CommandCounterIncrement, so
     * that the TOAST table will be visible for insertion.
     */
    toastid = OldHeap->rd_rel->reltoastrelid;
    if (OidIsValid(toastid))
    {
        /* keep the existing toast table's reloptions, if any */
        tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(toastid));
        if (!HeapTupleIsValid(tuple))
            elog(ERROR, "cache lookup failed for relation %u", toastid);
        reloptions = SysCacheGetAttr(RELOID, tuple, Anum_pg_class_reloptions,
                                     &isNull);
        if (isNull)
            reloptions = (Datum) 0;

        NewHeapCreateToastTable(OIDNewHeap, reloptions, lockmode);

        ReleaseSysCache(tuple);
    }

    table_close(OldHeap, NoLock);

    return OIDNewHeap;
}

/*
 * Do the physical copying of table data.
 *
 * There are three output parameters:
 * *pSwapToastByContent is set true if toast tables must be swapped by content.
 * *pFreezeXid receives the TransactionId used as freeze cutoff point.
 * *pCutoffMulti receives the MultiXactId used as a cutoff point.
 */
static void
copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex, bool verbose,
                bool *pSwapToastByContent, TransactionId *pFreezeXid,
                MultiXactId *pCutoffMulti)
{
    Relation    NewHeap,
                OldHeap,
                OldIndex;
    Relation    relRelation;
    HeapTuple   reltup;
    Form_pg_class relform;
    TupleDesc   oldTupDesc PG_USED_FOR_ASSERTS_ONLY;
    TupleDesc   newTupDesc PG_USED_FOR_ASSERTS_ONLY;
    TransactionId OldestXmin;
    TransactionId FreezeXid;
    MultiXactId MultiXactCutoff;
    bool        use_sort;
    double      num_tuples = 0,
                tups_vacuumed = 0,
                tups_recently_dead = 0;
    BlockNumber num_pages;
    int         elevel = verbose ? INFO : DEBUG2;
    PGRUsage    ru0;

    pg_rusage_init(&ru0);

    /*
     * Open the relations we need.
     */
    NewHeap = table_open(OIDNewHeap, AccessExclusiveLock);
    OldHeap = table_open(OIDOldHeap, AccessExclusiveLock);
    if (OidIsValid(OIDOldIndex))
        OldIndex = index_open(OIDOldIndex, AccessExclusiveLock);
    else
        OldIndex = NULL;

    /*
     * Their tuple descriptors should be exactly alike, but here we only need
     * assume that they have the same number of columns.
     */
    oldTupDesc = RelationGetDescr(OldHeap);
    newTupDesc = RelationGetDescr(NewHeap);
    Assert(newTupDesc->natts == oldTupDesc->natts);

    /*
     * If the OldHeap has a toast table, get lock on the toast table to keep
     * it from being vacuumed.  This is needed because autovacuum processes
     * toast tables independently of their main tables, with no lock on the
     * latter.  If an autovacuum were to start on the toast table after we
     * compute our OldestXmin below, it would use a later OldestXmin, and then
     * possibly remove as DEAD toast tuples belonging to main tuples we think
     * are only RECENTLY_DEAD.  Then we'd fail while trying to copy those
     * tuples.
     *
     * We don't need to open the toast relation here, just lock it.  The lock
     * will be held till end of transaction.
     */
    if (OldHeap->rd_rel->reltoastrelid)
        LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock);

    /*
     * If both tables have TOAST tables, perform toast swap by content.  It is
     * possible that the old table has a toast table but the new one doesn't,
     * if toastable columns have been dropped.  In that case we have to do
     * swap by links.  This is okay because swap by content is only essential
     * for system catalogs, and we don't support schema changes for them.
     */
    if (OldHeap->rd_rel->reltoastrelid && NewHeap->rd_rel->reltoastrelid)
    {
        *pSwapToastByContent = true;

        /*
         * When doing swap by content, any toast pointers written into NewHeap
         * must use the old toast table's OID, because that's where the toast
         * data will eventually be found.  Set this up by setting rd_toastoid.
         * This also tells toast_save_datum() to preserve the toast value
         * OIDs, which we want so as not to invalidate toast pointers in
         * system catalog caches, and to avoid making multiple copies of a
         * single toast value.
         *
         * Note that we must hold NewHeap open until we are done writing data,
         * since the relcache will not guarantee to remember this setting once
         * the relation is closed.  Also, this technique depends on the fact
         * that no one will try to read from the NewHeap until after we've
         * finished writing it and swapping the rels --- otherwise they could
         * follow the toast pointers to the wrong place.  (It would actually
         * work for values copied over from the old toast table, but not for
         * any values that we toast which were previously not toasted.)
         */
        NewHeap->rd_toastoid = OldHeap->rd_rel->reltoastrelid;
    }
    else
        *pSwapToastByContent = false;

    /*
     * Compute xids used to freeze and weed out dead tuples and multixacts.
     * Since we're going to rewrite the whole table anyway, there's no reason
     * not to be aggressive about this.
     */
    vacuum_set_xid_limits(OldHeap, 0, 0, 0, 0,
                          &OldestXmin, &FreezeXid, NULL, &MultiXactCutoff,
                          NULL);

    /*
     * FreezeXid will become the table's new relfrozenxid, and that mustn't go
     * backwards, so take the max.
     */
    if (TransactionIdIsValid(OldHeap->rd_rel->relfrozenxid) &&
        TransactionIdPrecedes(FreezeXid, OldHeap->rd_rel->relfrozenxid))
        FreezeXid = OldHeap->rd_rel->relfrozenxid;

    /*
     * MultiXactCutoff, similarly, shouldn't go backwards either.
     */
    if (MultiXactIdIsValid(OldHeap->rd_rel->relminmxid) &&
        MultiXactIdPrecedes(MultiXactCutoff, OldHeap->rd_rel->relminmxid))
        MultiXactCutoff = OldHeap->rd_rel->relminmxid;

    /*
     * Decide whether to use an indexscan or seqscan-and-optional-sort to scan
     * the OldHeap.  We know how to use a sort to duplicate the ordering of a
     * btree index, and will use seqscan-and-sort for that case if the planner
     * tells us it's cheaper.  Otherwise, always indexscan if an index is
     * provided, else plain seqscan.
     */
    if (OldIndex != NULL && OldIndex->rd_rel->relam == BTREE_AM_OID)
        use_sort = plan_cluster_use_sort(OIDOldHeap, OIDOldIndex);
    else
        use_sort = false;

    /* Log what we're doing */
    if (OldIndex != NULL && !use_sort)
        ereport(elevel,
                (errmsg("clustering \"%s.%s\" using index scan on \"%s\"",
                        get_namespace_name(RelationGetNamespace(OldHeap)),
                        RelationGetRelationName(OldHeap),
                        RelationGetRelationName(OldIndex))));
    else if (use_sort)
        ereport(elevel,
                (errmsg("clustering \"%s.%s\" using sequential scan and sort",
                        get_namespace_name(RelationGetNamespace(OldHeap)),
                        RelationGetRelationName(OldHeap))));
    else
        ereport(elevel,
                (errmsg("vacuuming \"%s.%s\"",
                        get_namespace_name(RelationGetNamespace(OldHeap)),
                        RelationGetRelationName(OldHeap))));

    /*
     * Hand of the actual copying to AM specific function, the generic code
     * cannot know how to deal with visibility across AMs. Note that this
     * routine is allowed to set FreezeXid / MultiXactCutoff to different
     * values (e.g. because the AM doesn't use freezing).
     */
    table_relation_copy_for_cluster(OldHeap, NewHeap, OldIndex, use_sort,
                                    OldestXmin, &FreezeXid, &MultiXactCutoff,
                                    &num_tuples, &tups_vacuumed,
                                    &tups_recently_dead);

    /* return selected values to caller, get set as relfrozenxid/minmxid */
    *pFreezeXid = FreezeXid;
    *pCutoffMulti = MultiXactCutoff;

    /* Reset rd_toastoid just to be tidy --- it shouldn't be looked at again */
    NewHeap->rd_toastoid = InvalidOid;

    num_pages = RelationGetNumberOfBlocks(NewHeap);

    /* Log what we did */
    ereport(elevel,
            (errmsg("\"%s\": found %.0f removable, %.0f nonremovable row versions in %u pages",
                    RelationGetRelationName(OldHeap),
                    tups_vacuumed, num_tuples,
                    RelationGetNumberOfBlocks(OldHeap)),
             errdetail("%.0f dead row versions cannot be removed yet.\n"
                       "%s.",
                       tups_recently_dead,
                       pg_rusage_show(&ru0))));

    if (OldIndex != NULL)
        index_close(OldIndex, NoLock);
    table_close(OldHeap, NoLock);
    table_close(NewHeap, NoLock);

    /* Update pg_class to reflect the correct values of pages and tuples. */
    relRelation = table_open(RelationRelationId, RowExclusiveLock);

    reltup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(OIDNewHeap));
    if (!HeapTupleIsValid(reltup))
        elog(ERROR, "cache lookup failed for relation %u", OIDNewHeap);
    relform = (Form_pg_class) GETSTRUCT(reltup);

    relform->relpages = num_pages;
    relform->reltuples = num_tuples;

    /* Don't update the stats for pg_class.  See swap_relation_files. */
    if (OIDOldHeap != RelationRelationId)
        CatalogTupleUpdate(relRelation, &reltup->t_self, reltup);
    else
        CacheInvalidateRelcacheByTuple(reltup);

    /* Clean up. */
    heap_freetuple(reltup);
    table_close(relRelation, RowExclusiveLock);

    /* Make the update visible */
    CommandCounterIncrement();
}

/*
 * Swap the physical files of two given relations.
 *
 * We swap the physical identity (reltablespace, relfilenode) while keeping the
 * same logical identities of the two relations.  relpersistence is also
 * swapped, which is critical since it determines where buffers live for each
 * relation.
 *
 * We can swap associated TOAST data in either of two ways: recursively swap
 * the physical content of the toast tables (and their indexes), or swap the
 * TOAST links in the given relations' pg_class entries.  The former is needed
 * to manage rewrites of shared catalogs (where we cannot change the pg_class
 * links) while the latter is the only way to handle cases in which a toast
 * table is added or removed altogether.
 *
 * Additionally, the first relation is marked with relfrozenxid set to
 * frozenXid.  It seems a bit ugly to have this here, but the caller would
 * have to do it anyway, so having it here saves a heap_update.  Note: in
 * the swap-toast-links case, we assume we don't need to change the toast
 * table's relfrozenxid: the new version of the toast table should already
 * have relfrozenxid set to RecentXmin, which is good enough.
 *
 * Lastly, if r2 and its toast table and toast index (if any) are mapped,
 * their OIDs are emitted into mapped_tables[].  This is hacky but beats
 * having to look the information up again later in finish_heap_swap.
 */
static void
swap_relation_files(Oid r1, Oid r2, bool target_is_pg_class,
                    bool swap_toast_by_content,
                    bool is_internal,
                    TransactionId frozenXid,
                    MultiXactId cutoffMulti,
                    Oid *mapped_tables)
{
    Relation    relRelation;
    HeapTuple   reltup1,
                reltup2;
    Form_pg_class relform1,
                relform2;
    Oid         relfilenode1,
                relfilenode2;
    Oid         swaptemp;
    char        swptmpchr;

    /* We need writable copies of both pg_class tuples. */
    relRelation = table_open(RelationRelationId, RowExclusiveLock);

    reltup1 = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(r1));
    if (!HeapTupleIsValid(reltup1))
        elog(ERROR, "cache lookup failed for relation %u", r1);
    relform1 = (Form_pg_class) GETSTRUCT(reltup1);

    reltup2 = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(r2));
    if (!HeapTupleIsValid(reltup2))
        elog(ERROR, "cache lookup failed for relation %u", r2);
    relform2 = (Form_pg_class) GETSTRUCT(reltup2);

    relfilenode1 = relform1->relfilenode;
    relfilenode2 = relform2->relfilenode;

    if (OidIsValid(relfilenode1) && OidIsValid(relfilenode2))
    {
        /*
         * Normal non-mapped relations: swap relfilenodes, reltablespaces,
         * relpersistence
         */
        Assert(!target_is_pg_class);

        swaptemp = relform1->relfilenode;
        relform1->relfilenode = relform2->relfilenode;
        relform2->relfilenode = swaptemp;

        swaptemp = relform1->reltablespace;
        relform1->reltablespace = relform2->reltablespace;
        relform2->reltablespace = swaptemp;

        swptmpchr = relform1->relpersistence;
        relform1->relpersistence = relform2->relpersistence;
        relform2->relpersistence = swptmpchr;

        /* Also swap toast links, if we're swapping by links */
        if (!swap_toast_by_content)
        {
            swaptemp = relform1->reltoastrelid;
            relform1->reltoastrelid = relform2->reltoastrelid;
            relform2->reltoastrelid = swaptemp;
        }
    }
    else
    {
        /*
         * Mapped-relation case.  Here we have to swap the relation mappings
         * instead of modifying the pg_class columns.  Both must be mapped.
         */
        if (OidIsValid(relfilenode1) || OidIsValid(relfilenode2))
            elog(ERROR, "cannot swap mapped relation \"%s\" with non-mapped relation",
                 NameStr(relform1->relname));

        /*
         * We can't change the tablespace nor persistence of a mapped rel, and
         * we can't handle toast link swapping for one either, because we must
         * not apply any critical changes to its pg_class row.  These cases
         * should be prevented by upstream permissions tests, so these checks
         * are non-user-facing emergency backstop.
         */
        if (relform1->reltablespace != relform2->reltablespace)
            elog(ERROR, "cannot change tablespace of mapped relation \"%s\"",
                 NameStr(relform1->relname));
        if (relform1->relpersistence != relform2->relpersistence)
            elog(ERROR, "cannot change persistence of mapped relation \"%s\"",
                 NameStr(relform1->relname));
        if (!swap_toast_by_content &&
            (relform1->reltoastrelid || relform2->reltoastrelid))
            elog(ERROR, "cannot swap toast by links for mapped relation \"%s\"",
                 NameStr(relform1->relname));

        /*
         * Fetch the mappings --- shouldn't fail, but be paranoid
         */
        relfilenode1 = RelationMapOidToFilenode(r1, relform1->relisshared);
        if (!OidIsValid(relfilenode1))
            elog(ERROR, "could not find relation mapping for relation \"%s\", OID %u",
                 NameStr(relform1->relname), r1);
        relfilenode2 = RelationMapOidToFilenode(r2, relform2->relisshared);
        if (!OidIsValid(relfilenode2))
            elog(ERROR, "could not find relation mapping for relation \"%s\", OID %u",
                 NameStr(relform2->relname), r2);

        /*
         * Send replacement mappings to relmapper.  Note these won't actually
         * take effect until CommandCounterIncrement.
         */
        RelationMapUpdateMap(r1, relfilenode2, relform1->relisshared, false);
        RelationMapUpdateMap(r2, relfilenode1, relform2->relisshared, false);

        /* Pass OIDs of mapped r2 tables back to caller */
        *mapped_tables++ = r2;
    }

    /*
     * In the case of a shared catalog, these next few steps will only affect
     * our own database's pg_class row; but that's okay, because they are all
     * noncritical updates.  That's also an important fact for the case of a
     * mapped catalog, because it's possible that we'll commit the map change
     * and then fail to commit the pg_class update.
     */

    /* set rel1's frozen Xid and minimum MultiXid */
    if (relform1->relkind != RELKIND_INDEX)
    {
        Assert(!TransactionIdIsValid(frozenXid) ||
               TransactionIdIsNormal(frozenXid));
        relform1->relfrozenxid = frozenXid;
        relform1->relminmxid = cutoffMulti;
    }

    /* swap size statistics too, since new rel has freshly-updated stats */
    {
        int32       swap_pages;
        float4      swap_tuples;
        int32       swap_allvisible;

        swap_pages = relform1->relpages;
        relform1->relpages = relform2->relpages;
        relform2->relpages = swap_pages;

        swap_tuples = relform1->reltuples;
        relform1->reltuples = relform2->reltuples;
        relform2->reltuples = swap_tuples;

        swap_allvisible = relform1->relallvisible;
        relform1->relallvisible = relform2->relallvisible;
        relform2->relallvisible = swap_allvisible;
    }

    /*
     * Update the tuples in pg_class --- unless the target relation of the
     * swap is pg_class itself.  In that case, there is zero point in making
     * changes because we'd be updating the old data that we're about to throw
     * away.  Because the real work being done here for a mapped relation is
     * just to change the relation map settings, it's all right to not update
     * the pg_class rows in this case. The most important changes will instead
     * performed later, in finish_heap_swap() itself.
     */
    if (!target_is_pg_class)
    {
        CatalogIndexState indstate;

        indstate = CatalogOpenIndexes(relRelation);
        CatalogTupleUpdateWithInfo(relRelation, &reltup1->t_self, reltup1,
                                   indstate);
        CatalogTupleUpdateWithInfo(relRelation, &reltup2->t_self, reltup2,
                                   indstate);
        CatalogCloseIndexes(indstate);
    }
    else
    {
        /* no update ... but we do still need relcache inval */
        CacheInvalidateRelcacheByTuple(reltup1);
        CacheInvalidateRelcacheByTuple(reltup2);
    }

    /*
     * Post alter hook for modified relations. The change to r2 is always
     * internal, but r1 depends on the invocation context.
     */
    InvokeObjectPostAlterHookArg(RelationRelationId, r1, 0,
                                 InvalidOid, is_internal);
    InvokeObjectPostAlterHookArg(RelationRelationId, r2, 0,
                                 InvalidOid, true);

    /*
     * If we have toast tables associated with the relations being swapped,
     * deal with them too.
     */
    if (relform1->reltoastrelid || relform2->reltoastrelid)
    {
        if (swap_toast_by_content)
        {
            if (relform1->reltoastrelid && relform2->reltoastrelid)
            {
                /* Recursively swap the contents of the toast tables */
                swap_relation_files(relform1->reltoastrelid,
                                    relform2->reltoastrelid,
                                    target_is_pg_class,
                                    swap_toast_by_content,
                                    is_internal,
                                    frozenXid,
                                    cutoffMulti,
                                    mapped_tables);
            }
            else
            {
                /* caller messed up */
                elog(ERROR, "cannot swap toast files by content when there's only one");
            }
        }
        else
        {
            /*
             * We swapped the ownership links, so we need to change dependency
             * data to match.
             *
             * NOTE: it is possible that only one table has a toast table.
             *
             * NOTE: at present, a TOAST table's only dependency is the one on
             * its owning table.  If more are ever created, we'd need to use
             * something more selective than deleteDependencyRecordsFor() to
             * get rid of just the link we want.
             */
            ObjectAddress baseobject,
                        toastobject;
            long        count;

            /*
             * We disallow this case for system catalogs, to avoid the
             * possibility that the catalog we're rebuilding is one of the
             * ones the dependency changes would change.  It's too late to be
             * making any data changes to the target catalog.
             */
            if (IsSystemClass(r1, relform1))
                elog(ERROR, "cannot swap toast files by links for system catalogs");

            /* Delete old dependencies */
            if (relform1->reltoastrelid)
            {
                count = deleteDependencyRecordsFor(RelationRelationId,
                                                   relform1->reltoastrelid,
                                                   false);
                if (count != 1)
                    elog(ERROR, "expected one dependency record for TOAST table, found %ld",
                         count);
            }
            if (relform2->reltoastrelid)
            {
                count = deleteDependencyRecordsFor(RelationRelationId,
                                                   relform2->reltoastrelid,
                                                   false);
                if (count != 1)
                    elog(ERROR, "expected one dependency record for TOAST table, found %ld",
                         count);
            }

            /* Register new dependencies */
            baseobject.classId = RelationRelationId;
            baseobject.objectSubId = 0;
            toastobject.classId = RelationRelationId;
            toastobject.objectSubId = 0;

            if (relform1->reltoastrelid)
            {
                baseobject.objectId = r1;
                toastobject.objectId = relform1->reltoastrelid;
                recordDependencyOn(&toastobject, &baseobject,
                                   DEPENDENCY_INTERNAL);
            }

            if (relform2->reltoastrelid)
            {
                baseobject.objectId = r2;
                toastobject.objectId = relform2->reltoastrelid;
                recordDependencyOn(&toastobject, &baseobject,
                                   DEPENDENCY_INTERNAL);
            }
        }
    }

    /*
     * If we're swapping two toast tables by content, do the same for their
     * valid index. The swap can actually be safely done only if the relations
     * have indexes.
     */
    if (swap_toast_by_content &&
        relform1->relkind == RELKIND_TOASTVALUE &&
        relform2->relkind == RELKIND_TOASTVALUE)
    {
        Oid         toastIndex1,
                    toastIndex2;

        /* Get valid index for each relation */
        toastIndex1 = toast_get_valid_index(r1,
                                            AccessExclusiveLock);
        toastIndex2 = toast_get_valid_index(r2,
                                            AccessExclusiveLock);

        swap_relation_files(toastIndex1,
                            toastIndex2,
                            target_is_pg_class,
                            swap_toast_by_content,
                            is_internal,
                            InvalidTransactionId,
                            InvalidMultiXactId,
                            mapped_tables);
    }

    /* Clean up. */
    heap_freetuple(reltup1);
    heap_freetuple(reltup2);

    table_close(relRelation, RowExclusiveLock);

    /*
     * Close both relcache entries' smgr links.  We need this kluge because
     * both links will be invalidated during upcoming CommandCounterIncrement.
     * Whichever of the rels is the second to be cleared will have a dangling
     * reference to the other's smgr entry.  Rather than trying to avoid this
     * by ordering operations just so, it's easiest to close the links first.
     * (Fortunately, since one of the entries is local in our transaction,
     * it's sufficient to clear out our own relcache this way; the problem
     * cannot arise for other backends when they see our update on the
     * non-transient relation.)
     *
     * Caution: the placement of this step interacts with the decision to
     * handle toast rels by recursion.  When we are trying to rebuild pg_class
     * itself, the smgr close on pg_class must happen after all accesses in
     * this function.
     */
    RelationCloseSmgrByOid(r1);
    RelationCloseSmgrByOid(r2);
}

/*
 * Remove the transient table that was built by make_new_heap, and finish
 * cleaning up (including rebuilding all indexes on the old heap).
 */
void
finish_heap_swap(Oid OIDOldHeap, Oid OIDNewHeap,
                 bool is_system_catalog,
                 bool swap_toast_by_content,
                 bool check_constraints,
                 bool is_internal,
                 TransactionId frozenXid,
                 MultiXactId cutoffMulti,
                 char newrelpersistence)
{
    ObjectAddress object;
    Oid         mapped_tables[4];
    int         reindex_flags;
    int         i;

    /* Report that we are now swapping relation files */
    pgstat_progress_update_param(PROGRESS_CLUSTER_PHASE,
                                 PROGRESS_CLUSTER_PHASE_SWAP_REL_FILES);

    /* Zero out possible results from swapped_relation_files */
    memset(mapped_tables, 0, sizeof(mapped_tables));

    /*
     * Swap the contents of the heap relations (including any toast tables).
     * Also set old heap's relfrozenxid to frozenXid.
     */
    swap_relation_files(OIDOldHeap, OIDNewHeap,
                        (OIDOldHeap == RelationRelationId),
                        swap_toast_by_content, is_internal,
                        frozenXid, cutoffMulti, mapped_tables);

    /*
     * If it's a system catalog, queue a sinval message to flush all catcaches
     * on the catalog when we reach CommandCounterIncrement.
     */
    if (is_system_catalog)
        CacheInvalidateCatalog(OIDOldHeap);

    /*
     * Rebuild each index on the relation (but not the toast table, which is
     * all-new at this point).  It is important to do this before the DROP
     * step because if we are processing a system catalog that will be used
     * during DROP, we want to have its indexes available.  There is no
     * advantage to the other order anyway because this is all transactional,
     * so no chance to reclaim disk space before commit.  We do not need a
     * final CommandCounterIncrement() because reindex_relation does it.
     *
     * Note: because index_build is called via reindex_relation, it will never
     * set indcheckxmin true for the indexes.  This is OK even though in some
     * sense we are building new indexes rather than rebuilding existing ones,
     * because the new heap won't contain any HOT chains at all, let alone
     * broken ones, so it can't be necessary to set indcheckxmin.
     */
    reindex_flags = REINDEX_REL_SUPPRESS_INDEX_USE;
    if (check_constraints)
        reindex_flags |= REINDEX_REL_CHECK_CONSTRAINTS;

    /*
     * Ensure that the indexes have the same persistence as the parent
     * relation.
     */
    if (newrelpersistence == RELPERSISTENCE_UNLOGGED)
        reindex_flags |= REINDEX_REL_FORCE_INDEXES_UNLOGGED;
    else if (newrelpersistence == RELPERSISTENCE_PERMANENT)
        reindex_flags |= REINDEX_REL_FORCE_INDEXES_PERMANENT;

    /* Report that we are now reindexing relations */
    pgstat_progress_update_param(PROGRESS_CLUSTER_PHASE,
                                 PROGRESS_CLUSTER_PHASE_REBUILD_INDEX);

    reindex_relation(OIDOldHeap, reindex_flags, 0);

    /* Report that we are now doing clean up */
    pgstat_progress_update_param(PROGRESS_CLUSTER_PHASE,
                                 PROGRESS_CLUSTER_PHASE_FINAL_CLEANUP);

    /*
     * If the relation being rebuild is pg_class, swap_relation_files()
     * couldn't update pg_class's own pg_class entry (check comments in
     * swap_relation_files()), thus relfrozenxid was not updated. That's
     * annoying because a potential reason for doing a VACUUM FULL is a
     * imminent or actual anti-wraparound shutdown.  So, now that we can
     * access the new relation using its indices, update relfrozenxid.
     * pg_class doesn't have a toast relation, so we don't need to update the
     * corresponding toast relation. Not that there's little point moving all
     * relfrozenxid updates here since swap_relation_files() needs to write to
     * pg_class for non-mapped relations anyway.
     */
    if (OIDOldHeap == RelationRelationId)
    {
        Relation    relRelation;
        HeapTuple   reltup;
        Form_pg_class relform;

        relRelation = table_open(RelationRelationId, RowExclusiveLock);

        reltup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(OIDOldHeap));
        if (!HeapTupleIsValid(reltup))
            elog(ERROR, "cache lookup failed for relation %u", OIDOldHeap);
        relform = (Form_pg_class) GETSTRUCT(reltup);

        relform->relfrozenxid = frozenXid;
        relform->relminmxid = cutoffMulti;

        CatalogTupleUpdate(relRelation, &reltup->t_self, reltup);

        table_close(relRelation, RowExclusiveLock);
    }

    /* Destroy new heap with old filenode */
    object.classId = RelationRelationId;
    object.objectId = OIDNewHeap;
    object.objectSubId = 0;

    /*
     * The new relation is local to our transaction and we know nothing
     * depends on it, so DROP_RESTRICT should be OK.
     */
    performDeletion(&object, DROP_RESTRICT, PERFORM_DELETION_INTERNAL);

    /* performDeletion does CommandCounterIncrement at end */

    /*
     * Now we must remove any relation mapping entries that we set up for the
     * transient table, as well as its toast table and toast index if any. If
     * we fail to do this before commit, the relmapper will complain about new
     * permanent map entries being added post-bootstrap.
     */
    for (i = 0; OidIsValid(mapped_tables[i]); i++)
        RelationMapRemoveMapping(mapped_tables[i]);

    /*
     * At this point, everything is kosher except that, if we did toast swap
     * by links, the toast table's name corresponds to the transient table.
     * The name is irrelevant to the backend because it's referenced by OID,
     * but users looking at the catalogs could be confused.  Rename it to
     * prevent this problem.
     *
     * Note no lock required on the relation, because we already hold an
     * exclusive lock on it.
     */
    if (!swap_toast_by_content)
    {
        Relation    newrel;

        newrel = table_open(OIDOldHeap, NoLock);
        if (OidIsValid(newrel->rd_rel->reltoastrelid))
        {
            Oid         toastidx;
            char        NewToastName[NAMEDATALEN];

            /* Get the associated valid index to be renamed */
            toastidx = toast_get_valid_index(newrel->rd_rel->reltoastrelid,
                                             AccessShareLock);

            /* rename the toast table ... */
            snprintf(NewToastName, NAMEDATALEN, "pg_toast_%u",
                     OIDOldHeap);
            RenameRelationInternal(newrel->rd_rel->reltoastrelid,
                                   NewToastName, true, false);

            /* ... and its valid index too. */
            snprintf(NewToastName, NAMEDATALEN, "pg_toast_%u_index",
                     OIDOldHeap);

            RenameRelationInternal(toastidx,
                                   NewToastName, true, true);
        }
        relation_close(newrel, NoLock);
    }

    /* if it's not a catalog table, clear any missing attribute settings */
    if (!is_system_catalog)
    {
        Relation    newrel;

        newrel = table_open(OIDOldHeap, NoLock);
        RelationClearMissing(newrel);
        relation_close(newrel, NoLock);
    }
}


/*
 * Get a list of tables that the current user owns and
 * have indisclustered set.  Return the list in a List * of RelToCluster
 * with the tableOid and the indexOid on which the table is already
 * clustered.
 */
static List *
get_tables_to_cluster(MemoryContext cluster_context)
{
    Relation    indRelation;
    TableScanDesc scan;
    ScanKeyData entry;
    HeapTuple   indexTuple;
    Form_pg_index index;
    MemoryContext old_context;
    RelToCluster *rvtc;
    List       *rvs = NIL;

    /*
     * Get all indexes that have indisclustered set and are owned by
     * appropriate user. System relations or nailed-in relations cannot ever
     * have indisclustered set, because CLUSTER will refuse to set it when
     * called with one of them as argument.
     */
    indRelation = table_open(IndexRelationId, AccessShareLock);
    ScanKeyInit(&entry,
                Anum_pg_index_indisclustered,
                BTEqualStrategyNumber, F_BOOLEQ,
                BoolGetDatum(true));
    scan = table_beginscan_catalog(indRelation, 1, &entry);
    while ((indexTuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
    {
        index = (Form_pg_index) GETSTRUCT(indexTuple);

        if (!pg_class_ownercheck(index->indrelid, GetUserId()))
            continue;

        /*
         * We have to build the list in a different memory context so it will
         * survive the cross-transaction processing
         */
        old_context = MemoryContextSwitchTo(cluster_context);

        rvtc = (RelToCluster *) palloc(sizeof(RelToCluster));
        rvtc->tableOid = index->indrelid;
        rvtc->indexOid = index->indexrelid;
        rvs = lappend(rvs, rvtc);

        MemoryContextSwitchTo(old_context);
    }
    table_endscan(scan);

    relation_close(indRelation, AccessShareLock);

    return rvs;
}