Force a checkpoint in CREATE DATABASE before starting to copy the files,

[PostgreSQL.git] / src / backend / commands / cluster.c

/*-------------------------------------------------------------------------
 *
 * cluster.c
 *        CLUSTER a table on an index.
 *
 * There is hardly anything left of Paul Brown's original implementation...
 *
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994-5, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *        $PostgreSQL$
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/genam.h"
#include "access/heapam.h"
#include "access/relscan.h"
#include "access/rewriteheap.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/indexing.h"
#include "catalog/namespace.h"
#include "catalog/toasting.h"
#include "commands/cluster.h"
#include "commands/tablecmds.h"
#include "commands/trigger.h"
#include "commands/vacuum.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "storage/procarray.h"
#include "utils/acl.h"
#include "utils/fmgroids.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/relcache.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
#include "utils/tqual.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_rel(RelToCluster *rv, bool recheck);
static void rebuild_relation(Relation OldHeap, Oid indexOid);
static TransactionId copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex);
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;
                RelToCluster rvtc;

                /* Find and lock the table */
                rel = heap_openrv(stmt->relation, AccessExclusiveLock);

                tableOid = RelationGetRelid(rel);

                /* Check permissions */
                if (!pg_class_ownercheck(tableOid, GetUserId()))
                        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                                                   RelationGetRelationName(rel));

                /*
                 * Reject clustering a remote temp table ... their local buffer
                 * manager is not going to cope.
                 */
                if (isOtherTempNamespace(RelationGetNamespace(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))
                        {
                                HeapTuple       idxtuple;
                                Form_pg_index indexForm;

                                indexOid = lfirst_oid(index);
                                idxtuple = SearchSysCache(INDEXRELID,
                                                                                  ObjectIdGetDatum(indexOid),
                                                                                  0, 0, 0);
                                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)));
                }

                /* All other checks are done in cluster_rel() */
                rvtc.tableOid = tableOid;
                rvtc.indexOid = indexOid;

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

                /* Do the job */
                cluster_rel(&rvtc, false);
        }
        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.
                 */
                PreventTransactionChain(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_MINSIZE,
                                                                                                ALLOCSET_DEFAULT_INITSIZE,
                                                                                                ALLOCSET_DEFAULT_MAXSIZE);

                /*
                 * 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());
                        cluster_rel(rvtc, true);
                        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 thru 7.3).
 *
 * Also create new indexes and swap the filenodes with the old indexes the
 * same way we do for the relation.  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.
 */
static void
cluster_rel(RelToCluster *rvtc, bool recheck)
{
        Relation        OldHeap;

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

        /*
         * 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(rvtc->tableOid, AccessExclusiveLock);

        /* If the table has gone away, we can skip processing it */
        if (!OldHeap)
                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(rvtc->tableOid, GetUserId()))
                {
                        relation_close(OldHeap, AccessExclusiveLock);
                        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
                 * check_index_is_clusterable which is redundant, but we leave it for
                 * extra safety.
                 */
                if (isOtherTempNamespace(RelationGetNamespace(OldHeap)))
                {
                        relation_close(OldHeap, AccessExclusiveLock);
                        return;
                }

                /*
                 * Check that the index still exists
                 */
                if (!SearchSysCacheExists(RELOID,
                                                                  ObjectIdGetDatum(rvtc->indexOid),
                                                                  0, 0, 0))
                {
                        relation_close(OldHeap, AccessExclusiveLock);
                        return;
                }

                /*
                 * Check that the index is still the one with indisclustered set.
                 */
                tuple = SearchSysCache(INDEXRELID,
                                                           ObjectIdGetDatum(rvtc->indexOid),
                                                           0, 0, 0);
                if (!HeapTupleIsValid(tuple))   /* probably can't happen */
                {
                        relation_close(OldHeap, AccessExclusiveLock);
                        return;
                }
                indexForm = (Form_pg_index) GETSTRUCT(tuple);
                if (!indexForm->indisclustered)
                {
                        ReleaseSysCache(tuple);
                        relation_close(OldHeap, AccessExclusiveLock);
                        return;
                }
                ReleaseSysCache(tuple);
        }

        /* Check index is valid to cluster on */
        check_index_is_clusterable(OldHeap, rvtc->indexOid, recheck);

        /* rebuild_relation does all the dirty work */
        rebuild_relation(OldHeap, rvtc->indexOid);

        /* NB: rebuild_relation does heap_close() on OldHeap */
}

/*
 * Verify that the specified index is a legitimate index to cluster on
 *
 * Side effect: obtains exclusive lock on the index.  The caller should
 * already have exclusive lock on the table, so the index lock is likely
 * redundant, but it seems best to grab it anyway to ensure the index
 * definition can't change under us.
 */
void
check_index_is_clusterable(Relation OldHeap, Oid indexOid, bool recheck)
{
        Relation        OldIndex;

        OldIndex = index_open(indexOid, AccessExclusiveLock);

        /*
         * 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))));

        /*
         * 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))
                ereport(ERROR,
                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                 errmsg("cannot cluster on partial index \"%s\"",
                                                RelationGetRelationName(OldIndex))));

        if (!OldIndex->rd_am->amclusterable)
                ereport(ERROR,
                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                 errmsg("cannot cluster on index \"%s\" because access method does not support clustering",
                                                RelationGetRelationName(OldIndex))));

        if (!OldIndex->rd_am->amindexnulls)
        {
                AttrNumber      colno;

                /*
                 * If the AM doesn't index nulls, then it's a partial index unless we
                 * can prove all the rows are non-null.  Note we only need look at the
                 * first column; multicolumn-capable AMs are *required* to index nulls
                 * in columns after the first.
                 */
                colno = OldIndex->rd_index->indkey.values[0];
                if (colno > 0)
                {
                        /* ordinary user attribute */
                        if (!OldHeap->rd_att->attrs[colno - 1]->attnotnull)
                                ereport(ERROR,
                                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                                 errmsg("cannot cluster on index \"%s\" because access method does not handle null values",
                                                                RelationGetRelationName(OldIndex)),
                                                 recheck
                                                 ? errhint("You might be able to work around this by marking column \"%s\" NOT NULL, or use ALTER TABLE ... SET WITHOUT CLUSTER to remove the cluster specification from the table.",
                                                 NameStr(OldHeap->rd_att->attrs[colno - 1]->attname))
                                                 : errhint("You might be able to work around this by marking column \"%s\" NOT NULL.",
                                          NameStr(OldHeap->rd_att->attrs[colno - 1]->attname))));
                }
                else if (colno < 0)
                {
                        /* system column --- okay, always non-null */
                }
                else
                        /* index expression, lose... */
                        ereport(ERROR,
                                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                         errmsg("cannot cluster on expressional index \"%s\" because its index access method does not handle null values",
                                                        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))));

        /*
         * Disallow clustering system relations.  This will definitely NOT work
         * for shared relations (we have no way to update pg_class rows in other
         * databases), nor for nailed-in-cache relations (the relfilenode values
         * for those are hardwired, see relcache.c).  It might work for other
         * system relations, but I ain't gonna risk it.
         */
        if (IsSystemRelation(OldHeap))
                ereport(ERROR,
                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                 errmsg("\"%s\" is a system catalog",
                                                RelationGetRelationName(OldHeap))));

        /*
         * Don't allow cluster on temp tables of other backends ... their local
         * buffer manager is not going to cope.
         */
        if (isOtherTempNamespace(RelationGetNamespace(OldHeap)))
                ereport(ERROR,
                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                           errmsg("cannot cluster 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, "CLUSTER");

        /* 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)
{
        HeapTuple       indexTuple;
        Form_pg_index indexForm;
        Relation        pg_index;
        ListCell   *index;

        /*
         * If the index is already marked clustered, no need to do anything.
         */
        if (OidIsValid(indexOid))
        {
                indexTuple = SearchSysCache(INDEXRELID,
                                                                        ObjectIdGetDatum(indexOid),
                                                                        0, 0, 0);
                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 = heap_open(IndexRelationId, RowExclusiveLock);

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

                indexTuple = SearchSysCacheCopy(INDEXRELID,
                                                                                ObjectIdGetDatum(thisIndexOid),
                                                                                0, 0, 0);
                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;
                        simple_heap_update(pg_index, &indexTuple->t_self, indexTuple);
                        CatalogUpdateIndexes(pg_index, indexTuple);
                        /* Ensure we see the update in the index's relcache entry */
                        CacheInvalidateRelcacheByRelid(thisIndexOid);
                }
                else if (thisIndexOid == indexOid)
                {
                        indexForm->indisclustered = true;
                        simple_heap_update(pg_index, &indexTuple->t_self, indexTuple);
                        CatalogUpdateIndexes(pg_index, indexTuple);
                        /* Ensure we see the update in the index's relcache entry */
                        CacheInvalidateRelcacheByRelid(thisIndexOid);
                }
                heap_freetuple(indexTuple);
        }

        heap_close(pg_index, RowExclusiveLock);
}

/*
 * rebuild_relation: rebuild an existing relation in index order
 *
 * OldHeap: table to rebuild --- must be opened and exclusive-locked!
 * indexOid: index to cluster by
 *
 * NB: this routine closes OldHeap at the right time; caller should not.
 */
static void
rebuild_relation(Relation OldHeap, Oid indexOid)
{
        Oid                     tableOid = RelationGetRelid(OldHeap);
        Oid                     tableSpace = OldHeap->rd_rel->reltablespace;
        Oid                     OIDNewHeap;
        char            NewHeapName[NAMEDATALEN];
        TransactionId frozenXid;
        ObjectAddress object;

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

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

        /*
         * 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.
         */
        snprintf(NewHeapName, sizeof(NewHeapName), "pg_temp_%u", tableOid);

        OIDNewHeap = make_new_heap(tableOid, NewHeapName, tableSpace);

        /*
         * We don't need CommandCounterIncrement() because make_new_heap did it.
         */

        /*
         * Copy the heap data into the new table in the desired order.
         */
        frozenXid = copy_heap_data(OIDNewHeap, tableOid, indexOid);

        /* To make the new heap's data visible (probably not needed?). */
        CommandCounterIncrement();

        /* Swap the physical files of the old and new heaps. */
        swap_relation_files(tableOid, OIDNewHeap, frozenXid);

        CommandCounterIncrement();

        /* 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);

        /* performDeletion does CommandCounterIncrement at end */

        /*
         * Rebuild each index on the relation (but not the toast table, which is
         * all-new at this point).      We do not need CommandCounterIncrement()
         * because reindex_relation does it.
         */
        reindex_relation(tableOid, false);
}

/*
 * Create the new table that we will fill with correctly-ordered data.
 */
Oid
make_new_heap(Oid OIDOldHeap, const char *NewName, Oid NewTableSpace)
{
        TupleDesc       OldHeapDesc,
                                tupdesc;
        Oid                     OIDNewHeap;
        Relation        OldHeap;
        HeapTuple       tuple;
        Datum           reloptions;
        bool            isNull;

        OldHeap = heap_open(OIDOldHeap, AccessExclusiveLock);
        OldHeapDesc = RelationGetDescr(OldHeap);

        /*
         * Need to make a copy of the tuple descriptor, since
         * heap_create_with_catalog modifies it.  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.
         */
        tupdesc = CreateTupleDescCopy(OldHeapDesc);

        /*
         * Use options of the old heap for new heap.
         */
        tuple = SearchSysCache(RELOID,
                                                   ObjectIdGetDatum(OIDOldHeap),
                                                   0, 0, 0);
        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;

        OIDNewHeap = heap_create_with_catalog(NewName,
                                                                                  RelationGetNamespace(OldHeap),
                                                                                  NewTableSpace,
                                                                                  InvalidOid,
                                                                                  OldHeap->rd_rel->relowner,
                                                                                  tupdesc,
                                                                                  NIL,
                                                                                  OldHeap->rd_rel->relkind,
                                                                                  OldHeap->rd_rel->relisshared,
                                                                                  true,
                                                                                  0,
                                                                                  ONCOMMIT_NOOP,
                                                                                  reloptions,
                                                                                  allowSystemTableMods);

        ReleaseSysCache(tuple);

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

        /*
         * If necessary, create a TOAST table for the new relation. Note that
         * AlterTableCreateToastTable ends with CommandCounterIncrement(), so that
         * the TOAST table will be visible for insertion.
         */
        AlterTableCreateToastTable(OIDNewHeap);

        heap_close(OldHeap, NoLock);

        return OIDNewHeap;
}

/*
 * Do the physical copying of heap data.  Returns the TransactionId used as
 * freeze cutoff point for the tuples.
 */
static TransactionId
copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex)
{
        Relation        NewHeap,
                                OldHeap,
                                OldIndex;
        TupleDesc       oldTupDesc;
        TupleDesc       newTupDesc;
        int                     natts;
        Datum      *values;
        bool       *isnull;
        IndexScanDesc scan;
        HeapTuple       tuple;
        bool            use_wal;
        TransactionId OldestXmin;
        TransactionId FreezeXid;
        RewriteState rwstate;

        /*
         * Open the relations we need.
         */
        NewHeap = heap_open(OIDNewHeap, AccessExclusiveLock);
        OldHeap = heap_open(OIDOldHeap, AccessExclusiveLock);
        OldIndex = index_open(OIDOldIndex, AccessExclusiveLock);

        /*
         * 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);

        /* Preallocate values/isnull arrays */
        natts = newTupDesc->natts;
        values = (Datum *) palloc(natts * sizeof(Datum));
        isnull = (bool *) palloc(natts * sizeof(bool));

        /*
         * We need to log the copied data in WAL iff WAL archiving is enabled AND
         * it's not a temp rel.
         */
        use_wal = XLogArchivingActive() && !NewHeap->rd_istemp;

        /* use_wal off requires rd_targblock be initially invalid */
        Assert(NewHeap->rd_targblock == InvalidBlockNumber);

        /*
         * compute xids used to freeze and weed out dead tuples.  We use -1
         * freeze_min_age to avoid having CLUSTER freeze tuples earlier than a
         * plain VACUUM would.
         */
        vacuum_set_xid_limits(-1, OldHeap->rd_rel->relisshared,
                                                  &OldestXmin, &FreezeXid);

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

        /* Initialize the rewrite operation */
        rwstate = begin_heap_rewrite(NewHeap, OldestXmin, FreezeXid, use_wal);

        /*
         * Scan through the OldHeap in OldIndex order and copy each tuple into the
         * NewHeap.  To ensure we see recently-dead tuples that still need to be
         * copied, we scan with SnapshotAny and use HeapTupleSatisfiesVacuum for
         * the visibility test.
         */
        scan = index_beginscan(OldHeap, OldIndex,
                                                   SnapshotAny, 0, (ScanKey) NULL);

        while ((tuple = index_getnext(scan, ForwardScanDirection)) != NULL)
        {
                HeapTuple       copiedTuple;
                bool            isdead;
                int                     i;

                CHECK_FOR_INTERRUPTS();

                /* Since we used no scan keys, should never need to recheck */
                if (scan->xs_recheck)
                        elog(ERROR, "CLUSTER does not support lossy index conditions");

                LockBuffer(scan->xs_cbuf, BUFFER_LOCK_SHARE);

                switch (HeapTupleSatisfiesVacuum(tuple->t_data, OldestXmin,
                                                                                 scan->xs_cbuf))
                {
                        case HEAPTUPLE_DEAD:
                                /* Definitely dead */
                                isdead = true;
                                break;
                        case HEAPTUPLE_LIVE:
                        case HEAPTUPLE_RECENTLY_DEAD:
                                /* Live or recently dead, must copy it */
                                isdead = false;
                                break;
                        case HEAPTUPLE_INSERT_IN_PROGRESS:

                                /*
                                 * We should not see this unless it's been inserted earlier in
                                 * our own transaction.
                                 */
                                if (!TransactionIdIsCurrentTransactionId(
                                                                          HeapTupleHeaderGetXmin(tuple->t_data)))
                                        elog(ERROR, "concurrent insert in progress");
                                /* treat as live */
                                isdead = false;
                                break;
                        case HEAPTUPLE_DELETE_IN_PROGRESS:

                                /*
                                 * We should not see this unless it's been deleted earlier in
                                 * our own transaction.
                                 */
                                Assert(!(tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI));
                                if (!TransactionIdIsCurrentTransactionId(
                                                                          HeapTupleHeaderGetXmax(tuple->t_data)))
                                        elog(ERROR, "concurrent delete in progress");
                                /* treat as recently dead */
                                isdead = false;
                                break;
                        default:
                                elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result");
                                isdead = false; /* keep compiler quiet */
                                break;
                }

                LockBuffer(scan->xs_cbuf, BUFFER_LOCK_UNLOCK);

                if (isdead)
                {
                        /* heap rewrite module still needs to see it... */
                        rewrite_heap_dead_tuple(rwstate, tuple);
                        continue;
                }

                /*
                 * We cannot simply copy the tuple as-is, for several reasons:
                 *
                 * 1. We'd like to squeeze out the values of any dropped columns, both
                 * to save space and to ensure we have no corner-case failures. (It's
                 * possible for example that the new table hasn't got a TOAST table
                 * and so is unable to store any large values of dropped cols.)
                 *
                 * 2. The tuple might not even be legal for the new table; this is
                 * currently only known to happen as an after-effect of ALTER TABLE
                 * SET WITHOUT OIDS.
                 *
                 * So, we must reconstruct the tuple from component Datums.
                 */
                heap_deform_tuple(tuple, oldTupDesc, values, isnull);

                /* Be sure to null out any dropped columns */
                for (i = 0; i < natts; i++)
                {
                        if (newTupDesc->attrs[i]->attisdropped)
                                isnull[i] = true;
                }

                copiedTuple = heap_form_tuple(newTupDesc, values, isnull);

                /* Preserve OID, if any */
                if (NewHeap->rd_rel->relhasoids)
                        HeapTupleSetOid(copiedTuple, HeapTupleGetOid(tuple));

                /* The heap rewrite module does the rest */
                rewrite_heap_tuple(rwstate, tuple, copiedTuple);

                heap_freetuple(copiedTuple);
        }

        index_endscan(scan);

        /* Write out any remaining tuples, and fsync if needed */
        end_heap_rewrite(rwstate);

        pfree(values);
        pfree(isnull);

        index_close(OldIndex, NoLock);
        heap_close(OldHeap, NoLock);
        heap_close(NewHeap, NoLock);

        return FreezeXid;
}

/*
 * Swap the physical files of two given relations.
 *
 * We swap the physical identity (reltablespace and relfilenode) while
 * keeping the same logical identities of the two relations.
 *
 * Also swap any TOAST links, so that the toast data moves along with
 * the main-table data.
 *
 * Additionally, the first relation is marked with relfrozenxid set to
 * frozenXid.  It seems a bit ugly to have this here, but all callers would
 * have to do it anyway, so having it here saves a heap_update.  Note: the
 * TOAST table needs no special handling, because since we swapped the links,
 * the entry for the TOAST table will now contain RecentXmin in relfrozenxid,
 * which is the correct value.
 */
void
swap_relation_files(Oid r1, Oid r2, TransactionId frozenXid)
{
        Relation        relRelation;
        HeapTuple       reltup1,
                                reltup2;
        Form_pg_class relform1,
                                relform2;
        Oid                     swaptemp;
        CatalogIndexState indstate;

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

        reltup1 = SearchSysCacheCopy(RELOID,
                                                                 ObjectIdGetDatum(r1),
                                                                 0, 0, 0);
        if (!HeapTupleIsValid(reltup1))
                elog(ERROR, "cache lookup failed for relation %u", r1);
        relform1 = (Form_pg_class) GETSTRUCT(reltup1);

        reltup2 = SearchSysCacheCopy(RELOID,
                                                                 ObjectIdGetDatum(r2),
                                                                 0, 0, 0);
        if (!HeapTupleIsValid(reltup2))
                elog(ERROR, "cache lookup failed for relation %u", r2);
        relform2 = (Form_pg_class) GETSTRUCT(reltup2);

        /*
         * Actually swap the fields in the two tuples
         */
        swaptemp = relform1->relfilenode;
        relform1->relfilenode = relform2->relfilenode;
        relform2->relfilenode = swaptemp;

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

        swaptemp = relform1->reltoastrelid;
        relform1->reltoastrelid = relform2->reltoastrelid;
        relform2->reltoastrelid = swaptemp;

        /* we should not swap reltoastidxid */

        /* set rel1's frozen Xid */
        Assert(TransactionIdIsNormal(frozenXid));
        relform1->relfrozenxid = frozenXid;

        /* swap size statistics too, since new rel has freshly-updated stats */
        {
                int4            swap_pages;
                float4          swap_tuples;

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

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

        /* Update the tuples in pg_class */
        simple_heap_update(relRelation, &reltup1->t_self, reltup1);
        simple_heap_update(relRelation, &reltup2->t_self, reltup2);

        /* Keep system catalogs current */
        indstate = CatalogOpenIndexes(relRelation);
        CatalogIndexInsert(indstate, reltup1);
        CatalogIndexInsert(indstate, reltup2);
        CatalogCloseIndexes(indstate);

        /*
         * If we have toast tables associated with the relations being swapped,
         * change their dependency links to re-associate them with their new
         * owning relations.  Otherwise the wrong one will get dropped ...
         *
         * NOTE: it is possible that only one table has a toast table; this can
         * happen in CLUSTER if there were dropped columns in the old table, and
         * in ALTER TABLE when adding or changing type of columns.
         *
         * 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 only the
         * link we want.
         */
        if (relform1->reltoastrelid || relform2->reltoastrelid)
        {
                ObjectAddress baseobject,
                                        toastobject;
                long            count;

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

        /*
         * Blow away the old relcache entries now.      We need this kluge because
         * relcache.c keeps a link to the smgr relation for the physical file, and
         * that will be out of date as soon as we do CommandCounterIncrement.
         * Whichever of the rels is the second to be cleared during cache
         * invalidation will have a dangling reference to an already-deleted smgr
         * relation.  Rather than trying to avoid this by ordering operations just
         * so, it's easiest to not have the relcache entries there at all.
         * (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-local relation.)
         */
        RelationForgetRelation(r1);
        RelationForgetRelation(r2);

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

        heap_close(relRelation, RowExclusiveLock);
}

/*
 * Get a list of tables that the current user owns and
 * have indisclustered set.  Return the list in a List * of rvsToCluster
 * with the tableOid and the indexOid on which the table is already
 * clustered.
 */
static List *
get_tables_to_cluster(MemoryContext cluster_context)
{
        Relation        indRelation;
        HeapScanDesc 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 = heap_open(IndexRelationId, AccessShareLock);
        ScanKeyInit(&entry,
                                Anum_pg_index_indisclustered,
                                BTEqualStrategyNumber, F_BOOLEQ,
                                BoolGetDatum(true));
        scan = heap_beginscan(indRelation, SnapshotNow, 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 = lcons(rvtc, rvs);

                MemoryContextSwitchTo(old_context);
        }
        heap_endscan(scan);

        relation_close(indRelation, AccessShareLock);

        return rvs;
}