cluster.c

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/*-------------------------------------------------------------------------
 *
 * 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) 1996-2025, 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 "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/pg_inherits.h"
#include "catalog/toasting.h"
#include "commands/cluster.h"
#include "commands/defrem.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/guc.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"
 
/*
 * 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 cluster_multiple_rels(List *rtcs, ClusterParams *params);
static void rebuild_relation(Relation OldHeap, Relation index, bool verbose);
static void copy_table_data(Relation NewHeap, Relation OldHeap, Relation OldIndex,
                            bool verbose, bool *pSwapToastByContent,
                            TransactionId *pFreezeXid, MultiXactId *pCutoffMulti);
static List *get_tables_to_cluster(MemoryContext cluster_context);
static List *get_tables_to_cluster_partitioned(MemoryContext cluster_context,
                                               Oid indexOid);
static bool cluster_is_permitted_for_relation(Oid relid, Oid userid);
 
 
/*---------------------------------------------------------------------------
 * 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(ParseState *pstate, ClusterStmt *stmt, bool isTopLevel)
{
    ListCell   *lc;
    ClusterParams params = {0};
    bool        verbose = false;
    Relation    rel = NULL;
    Oid         indexOid = InvalidOid;
    MemoryContext cluster_context;
    List       *rtcs;
 
    /* Parse option list */
    foreach(lc, stmt->params)
    {
        DefElem    *opt = (DefElem *) lfirst(lc);
 
        if (strcmp(opt->defname, "verbose") == 0)
            verbose = defGetBoolean(opt);
        else
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("unrecognized CLUSTER option \"%s\"",
                            opt->defname),
                     parser_errposition(pstate, opt->location)));
    }
 
    params.options = (verbose ? CLUOPT_VERBOSE : 0);
 
    if (stmt->relation != NULL)
    {
        /* This is the single-relation case. */
        Oid         tableOid;
 
        /*
         * Find, lock, and check permissions on the table.  We obtain
         * AccessExclusiveLock right away to avoid lock-upgrade hazard in the
         * single-transaction case.
         */
        tableOid = RangeVarGetRelidExtended(stmt->relation,
                                            AccessExclusiveLock,
                                            0,
                                            RangeVarCallbackMaintainsTable,
                                            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")));
 
        if (stmt->indexname == NULL)
        {
            ListCell   *index;
 
            /* We need to find the index that has indisclustered set. */
            foreach(index, RelationGetIndexList(rel))
            {
                indexOid = lfirst_oid(index);
                if (get_index_isclustered(indexOid))
                    break;
                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)));
        }
 
        /* For non-partitioned tables, do what we came here to do. */
        if (rel->rd_rel->relkind != RELKIND_PARTITIONED_TABLE)
        {
            cluster_rel(rel, indexOid, &params);
            /* cluster_rel closes the relation, but keeps lock */
 
            return;
        }
    }
 
    /*
     * By here, we know we are in a multi-table situation.  In order to avoid
     * holding locks for too long, we want to process each table in its own
     * transaction.  This forces us to disallow running inside a user
     * transaction block.
     */
    PreventInTransactionBlock(isTopLevel, "CLUSTER");
 
    /* Also, we need a memory context to hold our list of relations */
    cluster_context = AllocSetContextCreate(PortalContext,
                                            "Cluster",
                                            ALLOCSET_DEFAULT_SIZES);
 
    /*
     * Either we're processing a partitioned table, or we were not given any
     * table name at all.  In either case, obtain a list of relations to
     * process.
     *
     * In the former case, an index name must have been given, so we don't
     * need to recheck its "indisclustered" bit, but we have to check that it
     * is an index that we can cluster on.  In the latter case, we set the
     * option bit to have indisclustered verified.
     *
     * Rechecking the relation itself is necessary here in all cases.
     */
    params.options |= CLUOPT_RECHECK;
    if (rel != NULL)
    {
        Assert(rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
        check_index_is_clusterable(rel, indexOid, AccessShareLock);
        rtcs = get_tables_to_cluster_partitioned(cluster_context, indexOid);
 
        /* close relation, releasing lock on parent table */
        table_close(rel, AccessExclusiveLock);
    }
    else
    {
        rtcs = get_tables_to_cluster(cluster_context);
        params.options |= CLUOPT_RECHECK_ISCLUSTERED;
    }
 
    /* Do the job. */
    cluster_multiple_rels(rtcs, &params);
 
    /* Start a new transaction for the cleanup work. */
    StartTransactionCommand();
 
    /* Clean up working storage */
    MemoryContextDelete(cluster_context);
}
 
/*
 * Given a list of relations to cluster, process each of them in a separate
 * transaction.
 *
 * We expect to be in a transaction at start, but there isn't one when we
 * return.
 */
static void
cluster_multiple_rels(List *rtcs, ClusterParams *params)
{
    ListCell   *lc;
 
    /* Commit to get out of starting transaction */
    PopActiveSnapshot();
    CommitTransactionCommand();
 
    /* Cluster the tables, each in a separate transaction */
    foreach(lc, rtcs)
    {
        RelToCluster *rtc = (RelToCluster *) lfirst(lc);
        Relation    rel;
 
        /* Start a new transaction for each relation. */
        StartTransactionCommand();
 
        /* functions in indexes may want a snapshot set */
        PushActiveSnapshot(GetTransactionSnapshot());
 
        rel = table_open(rtc->tableOid, AccessExclusiveLock);
 
        /* Process this table */
        cluster_rel(rel, rtc->indexOid, params);
        /* cluster_rel closes the relation, but keeps lock */
 
        PopActiveSnapshot();
        CommitTransactionCommand();
    }
}
 
/*
 * cluster_rel
 *
 * This clusters the table by creating a new, clustered table and
 * swapping the relfilenumbers 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.
 *
 * 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(Relation OldHeap, Oid indexOid, ClusterParams *params)
{
    Oid         tableOid = RelationGetRelid(OldHeap);
    Oid         save_userid;
    int         save_sec_context;
    int         save_nestlevel;
    bool        verbose = ((params->options & CLUOPT_VERBOSE) != 0);
    bool        recheck = ((params->options & CLUOPT_RECHECK) != 0);
    Relation    index;
 
    Assert(CheckRelationLockedByMe(OldHeap, AccessExclusiveLock, false));
 
    /* 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);
 
    /*
     * Switch to the table owner's userid, so that any index functions are run
     * as that user.  Also lock down security-restricted operations and
     * arrange to make GUC variable changes local to this command.
     */
    GetUserIdAndSecContext(&save_userid, &save_sec_context);
    SetUserIdAndSecContext(OldHeap->rd_rel->relowner,
                           save_sec_context | SECURITY_RESTRICTED_OPERATION);
    save_nestlevel = NewGUCNestLevel();
    RestrictSearchPath();
 
    /*
     * 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)
    {
        /* Check that the user still has privileges for the relation */
        if (!cluster_is_permitted_for_relation(tableOid, save_userid))
        {
            relation_close(OldHeap, AccessExclusiveLock);
            goto out;
        }
 
        /*
         * 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 or on a partitioned
         * table), 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);
            goto out;
        }
 
        if (OidIsValid(indexOid))
        {
            /*
             * Check that the index still exists
             */
            if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(indexOid)))
            {
                relation_close(OldHeap, AccessExclusiveLock);
                goto out;
            }
 
            /*
             * Check that the index is still the one with indisclustered set,
             * if needed.
             */
            if ((params->options & CLUOPT_RECHECK_ISCLUSTERED) != 0 &&
                !get_index_isclustered(indexOid))
            {
                relation_close(OldHeap, AccessExclusiveLock);
                goto out;
            }
        }
    }
 
    /*
     * 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))
    {
        /* verify the index is good and lock it */
        check_index_is_clusterable(OldHeap, indexOid, AccessExclusiveLock);
        /* also open it */
        index = index_open(indexOid, NoLock);
    }
    else
        index = NULL;
 
    /*
     * 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);
        goto out;
    }
 
    Assert(OldHeap->rd_rel->relkind == RELKIND_RELATION ||
           OldHeap->rd_rel->relkind == RELKIND_MATVIEW ||
           OldHeap->rd_rel->relkind == RELKIND_TOASTVALUE);
 
    /*
     * 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, index, verbose);
    /* rebuild_relation closes OldHeap, and index if valid */
 
out:
    /* Roll back any GUC changes executed by index functions */
    AtEOXact_GUC(false, save_nestlevel);
 
    /* Restore userid and security context */
    SetUserIdAndSecContext(save_userid, save_sec_context);
 
    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, 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))
    {
        if (get_index_isclustered(indexOid))
            return;
    }
 
    /*
     * 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.
 * index: index to cluster by, or NULL to rewrite in physical order.
 *
 * On entry, heap and index (if one is given) must be open, and
 * AccessExclusiveLock held on them.
 * On exit, they are closed, but locks on them are not released.
 */
static void
rebuild_relation(Relation OldHeap, Relation index, bool verbose)
{
    Oid         tableOid = RelationGetRelid(OldHeap);
    Oid         accessMethod = OldHeap->rd_rel->relam;
    Oid         tableSpace = OldHeap->rd_rel->reltablespace;
    Oid         OIDNewHeap;
    Relation    NewHeap;
    char        relpersistence;
    bool        is_system_catalog;
    bool        swap_toast_by_content;
    TransactionId frozenXid;
    MultiXactId cutoffMulti;
 
    Assert(CheckRelationLockedByMe(OldHeap, AccessExclusiveLock, false) &&
           (index == NULL || CheckRelationLockedByMe(index, AccessExclusiveLock, false)));
 
    if (index)
        /* Mark the correct index as clustered */
        mark_index_clustered(OldHeap, RelationGetRelid(index), true);
 
    /* Remember info about rel before closing OldHeap */
    relpersistence = OldHeap->rd_rel->relpersistence;
    is_system_catalog = IsSystemRelation(OldHeap);
 
    /*
     * Create the transient table that will receive the re-ordered data.
     *
     * OldHeap is already locked, so no need to lock it again.  make_new_heap
     * obtains AccessExclusiveLock on the new heap and its toast table.
     */
    OIDNewHeap = make_new_heap(tableOid, tableSpace,
                               accessMethod,
                               relpersistence,
                               NoLock);
    Assert(CheckRelationOidLockedByMe(OIDNewHeap, AccessExclusiveLock, false));
    NewHeap = table_open(OIDNewHeap, NoLock);
 
    /* Copy the heap data into the new table in the desired order */
    copy_table_data(NewHeap, OldHeap, index, verbose,
                    &swap_toast_by_content, &frozenXid, &cutoffMulti);
 
 
    /* Close relcache entries, but keep lock until transaction commit */
    table_close(OldHeap, NoLock);
    if (index)
        index_close(index, NoLock);
 
    /*
     * Close the new relation so it can be dropped as soon as the storage is
     * swapped. The relation is not visible to others, so no need to unlock it
     * explicitly.
     */
    table_close(NewHeap, NoLock);
 
    /*
     * 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 will have the
 * specified physical storage properties NewTableSpace, NewAccessMethod, and
 * relpersistence.
 *
 * 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, Oid NewAccessMethod,
              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,
                                          NewAccessMethod,
                                          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, toastid);
 
        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(Relation NewHeap, Relation OldHeap, Relation OldIndex, bool verbose,
                bool *pSwapToastByContent, TransactionId *pFreezeXid,
                MultiXactId *pCutoffMulti)
{
    Relation    relRelation;
    HeapTuple   reltup;
    Form_pg_class relform;
    TupleDesc   oldTupDesc PG_USED_FOR_ASSERTS_ONLY;
    TupleDesc   newTupDesc PG_USED_FOR_ASSERTS_ONLY;
    VacuumParams params;
    struct VacuumCutoffs cutoffs;
    bool        use_sort;
    double      num_tuples = 0,
                tups_vacuumed = 0,
                tups_recently_dead = 0;
    BlockNumber num_pages;
    int         elevel = verbose ? INFO : DEBUG2;
    PGRUsage    ru0;
    char       *nspname;
 
    pg_rusage_init(&ru0);
 
    /* Store a copy of the namespace name for logging purposes */
    nspname = get_namespace_name(RelationGetNamespace(OldHeap));
 
    /*
     * 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.
     */
    memset(&params, 0, sizeof(VacuumParams));
    vacuum_get_cutoffs(OldHeap, &params, &cutoffs);
 
    /*
     * FreezeXid will become the table's new relfrozenxid, and that mustn't go
     * backwards, so take the max.
     */
    {
        TransactionId relfrozenxid = OldHeap->rd_rel->relfrozenxid;
 
        if (TransactionIdIsValid(relfrozenxid) &&
            TransactionIdPrecedes(cutoffs.FreezeLimit, relfrozenxid))
            cutoffs.FreezeLimit = relfrozenxid;
    }
 
    /*
     * MultiXactCutoff, similarly, shouldn't go backwards either.
     */
    {
        MultiXactId relminmxid = OldHeap->rd_rel->relminmxid;
 
        if (MultiXactIdIsValid(relminmxid) &&
            MultiXactIdPrecedes(cutoffs.MultiXactCutoff, relminmxid))
            cutoffs.MultiXactCutoff = 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(RelationGetRelid(OldHeap),
                                         RelationGetRelid(OldIndex));
    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\"",
                        nspname,
                        RelationGetRelationName(OldHeap),
                        RelationGetRelationName(OldIndex))));
    else if (use_sort)
        ereport(elevel,
                (errmsg("clustering \"%s.%s\" using sequential scan and sort",
                        nspname,
                        RelationGetRelationName(OldHeap))));
    else
        ereport(elevel,
                (errmsg("vacuuming \"%s.%s\"",
                        nspname,
                        RelationGetRelationName(OldHeap))));
 
    /*
     * Hand off 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,
                                    cutoffs.OldestXmin, &cutoffs.FreezeLimit,
                                    &cutoffs.MultiXactCutoff,
                                    &num_tuples, &tups_vacuumed,
                                    &tups_recently_dead);
 
    /* return selected values to caller, get set as relfrozenxid/minmxid */
    *pFreezeXid = cutoffs.FreezeLimit;
    *pCutoffMulti = cutoffs.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.%s\": found %.0f removable, %.0f nonremovable row versions in %u pages",
                    nspname,
                    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))));
 
    /* Update pg_class to reflect the correct values of pages and tuples. */
    relRelation = table_open(RelationRelationId, RowExclusiveLock);
 
    reltup = SearchSysCacheCopy1(RELOID,
                                 ObjectIdGetDatum(RelationGetRelid(NewHeap)));
    if (!HeapTupleIsValid(reltup))
        elog(ERROR, "cache lookup failed for relation %u",
             RelationGetRelid(NewHeap));
    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 (RelationGetRelid(OldHeap) != 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, relfilenumber) 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;
    RelFileNumber relfilenumber1,
                relfilenumber2;
    RelFileNumber swaptemp;
    char        swptmpchr;
    Oid         relam1,
                relam2;
 
    /* 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);
 
    relfilenumber1 = relform1->relfilenode;
    relfilenumber2 = relform2->relfilenode;
    relam1 = relform1->relam;
    relam2 = relform2->relam;
 
    if (RelFileNumberIsValid(relfilenumber1) &&
        RelFileNumberIsValid(relfilenumber2))
    {
        /*
         * Normal non-mapped relations: swap relfilenumbers, 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;
 
        swaptemp = relform1->relam;
        relform1->relam = relform2->relam;
        relform2->relam = 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 (RelFileNumberIsValid(relfilenumber1) ||
            RelFileNumberIsValid(relfilenumber2))
            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 (relform1->relam != relform2->relam)
            elog(ERROR, "cannot change access method 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
         */
        relfilenumber1 = RelationMapOidToFilenumber(r1, relform1->relisshared);
        if (!RelFileNumberIsValid(relfilenumber1))
            elog(ERROR, "could not find relation mapping for relation \"%s\", OID %u",
                 NameStr(relform1->relname), r1);
        relfilenumber2 = RelationMapOidToFilenumber(r2, relform2->relisshared);
        if (!RelFileNumberIsValid(relfilenumber2))
            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, relfilenumber2, relform1->relisshared, false);
        RelationMapUpdateMap(r2, relfilenumber1, relform2->relisshared, false);
 
        /* Pass OIDs of mapped r2 tables back to caller */
        *mapped_tables++ = r2;
    }
 
    /*
     * Recognize that rel1's relfilenumber (swapped from rel2) is new in this
     * subtransaction. The rel2 storage (swapped from rel1) may or may not be
     * new.
     */
    {
        Relation    rel1,
                    rel2;
 
        rel1 = relation_open(r1, NoLock);
        rel2 = relation_open(r2, NoLock);
        rel2->rd_createSubid = rel1->rd_createSubid;
        rel2->rd_newRelfilelocatorSubid = rel1->rd_newRelfilelocatorSubid;
        rel2->rd_firstRelfilelocatorSubid = rel1->rd_firstRelfilelocatorSubid;
        RelationAssumeNewRelfilelocator(rel1);
        relation_close(rel1, NoLock);
        relation_close(rel2, NoLock);
    }
 
    /*
     * 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;
        int32       swap_allfrozen;
 
        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;
 
        swap_allfrozen = relform1->relallfrozen;
        relform1->relallfrozen = relform2->relallfrozen;
        relform2->relallfrozen = swap_allfrozen;
    }
 
    /*
     * 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);
    }
 
    /*
     * Now that pg_class has been updated with its relevant information for
     * the swap, update the dependency of the relations to point to their new
     * table AM, if it has changed.
     */
    if (relam1 != relam2)
    {
        if (changeDependencyFor(RelationRelationId,
                                r1,
                                AccessMethodRelationId,
                                relam1,
                                relam2) != 1)
            elog(ERROR, "could not change access method dependency for relation \"%s.%s\"",
                 get_namespace_name(get_rel_namespace(r1)),
                 get_rel_name(r1));
        if (changeDependencyFor(RelationRelationId,
                                r2,
                                AccessMethodRelationId,
                                relam2,
                                relam1) != 1)
            elog(ERROR, "could not change access method dependency for relation \"%s.%s\"",
                 get_namespace_name(get_rel_namespace(r2)),
                 get_rel_name(r2));
    }
 
    /*
     * 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);
}
 
/*
 * 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;
    ReindexParams reindex_params = {0};
    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(NULL, OIDOldHeap, reindex_flags, &reindex_params);
 
    /* Report that we are now doing clean up */
    pgstat_progress_update_param(PROGRESS_CLUSTER_PHASE,
                                 PROGRESS_CLUSTER_PHASE_FINAL_CLEANUP);
 
    /*
     * If the relation being rebuilt 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 filenumber */
    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,
                                             NoLock);
 
            /* 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);
 
            /*
             * Reset the relrewrite for the toast. The command-counter
             * increment is required here as we are about to update the tuple
             * that is updated as part of RenameRelationInternal.
             */
            CommandCounterIncrement();
            ResetRelRewrite(newrel->rd_rel->reltoastrelid);
        }
        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 has privileges on and
 * have indisclustered set.  Return the list in a List * of RelToCluster
 * (stored in the specified memory context), each one giving 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;
    List       *rtcs = NIL;
 
    /*
     * Get all indexes that have indisclustered set and that the current user
     * has the appropriate privileges for.
     */
    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)
    {
        RelToCluster *rtc;
 
        index = (Form_pg_index) GETSTRUCT(indexTuple);
 
        if (!cluster_is_permitted_for_relation(index->indrelid, GetUserId()))
            continue;
 
        /* Use a permanent memory context for the result list */
        old_context = MemoryContextSwitchTo(cluster_context);
 
        rtc = (RelToCluster *) palloc(sizeof(RelToCluster));
        rtc->tableOid = index->indrelid;
        rtc->indexOid = index->indexrelid;
        rtcs = lappend(rtcs, rtc);
 
        MemoryContextSwitchTo(old_context);
    }
    table_endscan(scan);
 
    relation_close(indRelation, AccessShareLock);
 
    return rtcs;
}
 
/*
 * Given an index on a partitioned table, return a list of RelToCluster for
 * all the children leaves tables/indexes.
 *
 * Like expand_vacuum_rel, but here caller must hold AccessExclusiveLock
 * on the table containing the index.
 */
static List *
get_tables_to_cluster_partitioned(MemoryContext cluster_context, Oid indexOid)
{
    List       *inhoids;
    ListCell   *lc;
    List       *rtcs = NIL;
    MemoryContext old_context;
 
    /* Do not lock the children until they're processed */
    inhoids = find_all_inheritors(indexOid, NoLock, NULL);
 
    foreach(lc, inhoids)
    {
        Oid         indexrelid = lfirst_oid(lc);
        Oid         relid = IndexGetRelation(indexrelid, false);
        RelToCluster *rtc;
 
        /* consider only leaf indexes */
        if (get_rel_relkind(indexrelid) != RELKIND_INDEX)
            continue;
 
        /*
         * It's possible that the user does not have privileges to CLUSTER the
         * leaf partition despite having such privileges on the partitioned
         * table.  We skip any partitions which the user is not permitted to
         * CLUSTER.
         */
        if (!cluster_is_permitted_for_relation(relid, GetUserId()))
            continue;
 
        /* Use a permanent memory context for the result list */
        old_context = MemoryContextSwitchTo(cluster_context);
 
        rtc = (RelToCluster *) palloc(sizeof(RelToCluster));
        rtc->tableOid = relid;
        rtc->indexOid = indexrelid;
        rtcs = lappend(rtcs, rtc);
 
        MemoryContextSwitchTo(old_context);
    }
 
    return rtcs;
}
 
/*
 * Return whether userid has privileges to CLUSTER relid.  If not, this
 * function emits a WARNING.
 */
static bool
cluster_is_permitted_for_relation(Oid relid, Oid userid)
{
    if (pg_class_aclcheck(relid, userid, ACL_MAINTAIN) == ACLCHECK_OK)
        return true;
 
    ereport(WARNING,
            (errmsg("permission denied to cluster \"%s\", skipping it",
                    get_rel_name(relid))));
    return false;
}