indexam.c

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/*-------------------------------------------------------------------------
 *
 * indexam.c
 *    general index access method routines
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/access/index/indexam.c
 *
 * INTERFACE ROUTINES
 *      index_open      - open an index relation by relation OID
 *      index_close     - close an index relation
 *      index_beginscan - start a scan of an index with amgettuple
 *      index_beginscan_bitmap - start a scan of an index with amgetbitmap
 *      index_rescan    - restart a scan of an index
 *      index_endscan   - end a scan
 *      index_insert    - insert an index tuple into a relation
 *      index_markpos   - mark a scan position
 *      index_restrpos  - restore a scan position
 *      index_parallelscan_estimate - estimate shared memory for parallel scan
 *      index_parallelscan_initialize - initialize parallel scan
 *      index_parallelrescan  - (re)start a parallel scan of an index
 *      index_beginscan_parallel - join parallel index scan
 *      index_getnext_tid   - get the next TID from a scan
 *      index_fetch_heap        - get the scan's next heap tuple
 *      index_getnext_slot  - get the next tuple from a scan
 *      index_getbitmap - get all tuples from a scan
 *      index_bulk_delete   - bulk deletion of index tuples
 *      index_vacuum_cleanup    - post-deletion cleanup of an index
 *      index_can_return    - does index support index-only scans?
 *      index_getprocid - get a support procedure OID
 *      index_getprocinfo - get a support procedure's lookup info
 *
 * NOTES
 *      This file contains the index_ routines which used
 *      to be a scattered collection of stuff in access/genam.
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/amapi.h"
#include "access/heapam.h"
#include "access/reloptions.h"
#include "access/relscan.h"
#include "access/tableam.h"
#include "access/transam.h"
#include "access/xlog.h"
#include "catalog/index.h"
#include "catalog/pg_amproc.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
#include "nodes/makefuncs.h"
#include "pgstat.h"
#include "storage/bufmgr.h"
#include "storage/lmgr.h"
#include "storage/predicate.h"
#include "utils/ruleutils.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
 
 
/* ----------------------------------------------------------------
 *                  macros used in index_ routines
 *
 * Note: the ReindexIsProcessingIndex() check in RELATION_CHECKS is there
 * to check that we don't try to scan or do retail insertions into an index
 * that is currently being rebuilt or pending rebuild.  This helps to catch
 * things that don't work when reindexing system catalogs.  The assertion
 * doesn't prevent the actual rebuild because we don't use RELATION_CHECKS
 * when calling the index AM's ambuild routine, and there is no reason for
 * ambuild to call its subsidiary routines through this file.
 * ----------------------------------------------------------------
 */
#define RELATION_CHECKS \
( \
    AssertMacro(RelationIsValid(indexRelation)), \
    AssertMacro(PointerIsValid(indexRelation->rd_indam)), \
    AssertMacro(!ReindexIsProcessingIndex(RelationGetRelid(indexRelation))) \
)
 
#define SCAN_CHECKS \
( \
    AssertMacro(IndexScanIsValid(scan)), \
    AssertMacro(RelationIsValid(scan->indexRelation)), \
    AssertMacro(PointerIsValid(scan->indexRelation->rd_indam)) \
)
 
#define CHECK_REL_PROCEDURE(pname) \
do { \
    if (indexRelation->rd_indam->pname == NULL) \
        elog(ERROR, "function \"%s\" is not defined for index \"%s\"", \
             CppAsString(pname), RelationGetRelationName(indexRelation)); \
} while(0)
 
#define CHECK_SCAN_PROCEDURE(pname) \
do { \
    if (scan->indexRelation->rd_indam->pname == NULL) \
        elog(ERROR, "function \"%s\" is not defined for index \"%s\"", \
             CppAsString(pname), RelationGetRelationName(scan->indexRelation)); \
} while(0)
 
static IndexScanDesc index_beginscan_internal(Relation indexRelation,
                                              int nkeys, int norderbys, Snapshot snapshot,
                                              ParallelIndexScanDesc pscan, bool temp_snap);
 
 
/* ----------------------------------------------------------------
 *                 index_ interface functions
 * ----------------------------------------------------------------
 */
 
/* ----------------
 *      index_open - open an index relation by relation OID
 *
 *      If lockmode is not "NoLock", the specified kind of lock is
 *      obtained on the index.  (Generally, NoLock should only be
 *      used if the caller knows it has some appropriate lock on the
 *      index already.)
 *
 *      An error is raised if the index does not exist.
 *
 *      This is a convenience routine adapted for indexscan use.
 *      Some callers may prefer to use relation_open directly.
 * ----------------
 */
Relation
index_open(Oid relationId, LOCKMODE lockmode)
{
    Relation    r;
 
    r = relation_open(relationId, lockmode);
 
    if (r->rd_rel->relkind != RELKIND_INDEX &&
        r->rd_rel->relkind != RELKIND_PARTITIONED_INDEX)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not an index",
                        RelationGetRelationName(r))));
 
    return r;
}
 
/* ----------------
 *      index_close - close an index relation
 *
 *      If lockmode is not "NoLock", we then release the specified lock.
 *
 *      Note that it is often sensible to hold a lock beyond index_close;
 *      in that case, the lock is released automatically at xact end.
 * ----------------
 */
void
index_close(Relation relation, LOCKMODE lockmode)
{
    LockRelId   relid = relation->rd_lockInfo.lockRelId;
 
    Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);
 
    /* The relcache does the real work... */
    RelationClose(relation);
 
    if (lockmode != NoLock)
        UnlockRelationId(&relid, lockmode);
}
 
/* ----------------
 *      index_insert - insert an index tuple into a relation
 * ----------------
 */
bool
index_insert(Relation indexRelation,
             Datum *values,
             bool *isnull,
             ItemPointer heap_t_ctid,
             Relation heapRelation,
             IndexUniqueCheck checkUnique,
             bool indexUnchanged,
             IndexInfo *indexInfo)
{
    RELATION_CHECKS;
    CHECK_REL_PROCEDURE(aminsert);
 
    if (!(indexRelation->rd_indam->ampredlocks))
        CheckForSerializableConflictIn(indexRelation,
                                       (ItemPointer) NULL,
                                       InvalidBlockNumber);
 
    return indexRelation->rd_indam->aminsert(indexRelation, values, isnull,
                                             heap_t_ctid, heapRelation,
                                             checkUnique, indexUnchanged,
                                             indexInfo);
}
 
/*
 * index_beginscan - start a scan of an index with amgettuple
 *
 * Caller must be holding suitable locks on the heap and the index.
 */
IndexScanDesc
index_beginscan(Relation heapRelation,
                Relation indexRelation,
                Snapshot snapshot,
                int nkeys, int norderbys)
{
    IndexScanDesc scan;
 
    Assert(snapshot != InvalidSnapshot);
 
    scan = index_beginscan_internal(indexRelation, nkeys, norderbys, snapshot, NULL, false);
 
    /*
     * Save additional parameters into the scandesc.  Everything else was set
     * up by RelationGetIndexScan.
     */
    scan->heapRelation = heapRelation;
    scan->xs_snapshot = snapshot;
 
    /* prepare to fetch index matches from table */
    scan->xs_heapfetch = table_index_fetch_begin(heapRelation);
 
    return scan;
}
 
/*
 * index_beginscan_bitmap - start a scan of an index with amgetbitmap
 *
 * As above, caller had better be holding some lock on the parent heap
 * relation, even though it's not explicitly mentioned here.
 */
IndexScanDesc
index_beginscan_bitmap(Relation indexRelation,
                       Snapshot snapshot,
                       int nkeys)
{
    IndexScanDesc scan;
 
    Assert(snapshot != InvalidSnapshot);
 
    scan = index_beginscan_internal(indexRelation, nkeys, 0, snapshot, NULL, false);
 
    /*
     * Save additional parameters into the scandesc.  Everything else was set
     * up by RelationGetIndexScan.
     */
    scan->xs_snapshot = snapshot;
 
    return scan;
}
 
/*
 * index_beginscan_internal --- common code for index_beginscan variants
 */
static IndexScanDesc
index_beginscan_internal(Relation indexRelation,
                         int nkeys, int norderbys, Snapshot snapshot,
                         ParallelIndexScanDesc pscan, bool temp_snap)
{
    IndexScanDesc scan;
 
    RELATION_CHECKS;
    CHECK_REL_PROCEDURE(ambeginscan);
 
    if (!(indexRelation->rd_indam->ampredlocks))
        PredicateLockRelation(indexRelation, snapshot);
 
    /*
     * We hold a reference count to the relcache entry throughout the scan.
     */
    RelationIncrementReferenceCount(indexRelation);
 
    /*
     * Tell the AM to open a scan.
     */
    scan = indexRelation->rd_indam->ambeginscan(indexRelation, nkeys,
                                                norderbys);
    /* Initialize information for parallel scan. */
    scan->parallel_scan = pscan;
    scan->xs_temp_snap = temp_snap;
 
    return scan;
}
 
/* ----------------
 *      index_rescan  - (re)start a scan of an index
 *
 * During a restart, the caller may specify a new set of scankeys and/or
 * orderbykeys; but the number of keys cannot differ from what index_beginscan
 * was told.  (Later we might relax that to "must not exceed", but currently
 * the index AMs tend to assume that scan->numberOfKeys is what to believe.)
 * To restart the scan without changing keys, pass NULL for the key arrays.
 * (Of course, keys *must* be passed on the first call, unless
 * scan->numberOfKeys is zero.)
 * ----------------
 */
void
index_rescan(IndexScanDesc scan,
             ScanKey keys, int nkeys,
             ScanKey orderbys, int norderbys)
{
    SCAN_CHECKS;
    CHECK_SCAN_PROCEDURE(amrescan);
 
    Assert(nkeys == scan->numberOfKeys);
    Assert(norderbys == scan->numberOfOrderBys);
 
    /* Release resources (like buffer pins) from table accesses */
    if (scan->xs_heapfetch)
        table_index_fetch_reset(scan->xs_heapfetch);
 
    scan->kill_prior_tuple = false; /* for safety */
    scan->xs_heap_continue = false;
 
    scan->indexRelation->rd_indam->amrescan(scan, keys, nkeys,
                                            orderbys, norderbys);
}
 
/* ----------------
 *      index_endscan - end a scan
 * ----------------
 */
void
index_endscan(IndexScanDesc scan)
{
    SCAN_CHECKS;
    CHECK_SCAN_PROCEDURE(amendscan);
 
    /* Release resources (like buffer pins) from table accesses */
    if (scan->xs_heapfetch)
    {
        table_index_fetch_end(scan->xs_heapfetch);
        scan->xs_heapfetch = NULL;
    }
 
    /* End the AM's scan */
    scan->indexRelation->rd_indam->amendscan(scan);
 
    /* Release index refcount acquired by index_beginscan */
    RelationDecrementReferenceCount(scan->indexRelation);
 
    if (scan->xs_temp_snap)
        UnregisterSnapshot(scan->xs_snapshot);
 
    /* Release the scan data structure itself */
    IndexScanEnd(scan);
}
 
/* ----------------
 *      index_markpos  - mark a scan position
 * ----------------
 */
void
index_markpos(IndexScanDesc scan)
{
    SCAN_CHECKS;
    CHECK_SCAN_PROCEDURE(ammarkpos);
 
    scan->indexRelation->rd_indam->ammarkpos(scan);
}
 
/* ----------------
 *      index_restrpos  - restore a scan position
 *
 * NOTE: this only restores the internal scan state of the index AM.  See
 * comments for ExecRestrPos().
 *
 * NOTE: For heap, in the presence of HOT chains, mark/restore only works
 * correctly if the scan's snapshot is MVCC-safe; that ensures that there's at
 * most one returnable tuple in each HOT chain, and so restoring the prior
 * state at the granularity of the index AM is sufficient.  Since the only
 * current user of mark/restore functionality is nodeMergejoin.c, this
 * effectively means that merge-join plans only work for MVCC snapshots.  This
 * could be fixed if necessary, but for now it seems unimportant.
 * ----------------
 */
void
index_restrpos(IndexScanDesc scan)
{
    Assert(IsMVCCSnapshot(scan->xs_snapshot));
 
    SCAN_CHECKS;
    CHECK_SCAN_PROCEDURE(amrestrpos);
 
    /* release resources (like buffer pins) from table accesses */
    if (scan->xs_heapfetch)
        table_index_fetch_reset(scan->xs_heapfetch);
 
    scan->kill_prior_tuple = false; /* for safety */
    scan->xs_heap_continue = false;
 
    scan->indexRelation->rd_indam->amrestrpos(scan);
}
 
/*
 * index_parallelscan_estimate - estimate shared memory for parallel scan
 *
 * Currently, we don't pass any information to the AM-specific estimator,
 * so it can probably only return a constant.  In the future, we might need
 * to pass more information.
 */
Size
index_parallelscan_estimate(Relation indexRelation, Snapshot snapshot)
{
    Size        nbytes;
 
    Assert(snapshot != InvalidSnapshot);
 
    RELATION_CHECKS;
 
    nbytes = offsetof(ParallelIndexScanDescData, ps_snapshot_data);
    nbytes = add_size(nbytes, EstimateSnapshotSpace(snapshot));
    nbytes = MAXALIGN(nbytes);
 
    /*
     * If amestimateparallelscan is not provided, assume there is no
     * AM-specific data needed.  (It's hard to believe that could work, but
     * it's easy enough to cater to it here.)
     */
    if (indexRelation->rd_indam->amestimateparallelscan != NULL)
        nbytes = add_size(nbytes,
                          indexRelation->rd_indam->amestimateparallelscan());
 
    return nbytes;
}
 
/*
 * index_parallelscan_initialize - initialize parallel scan
 *
 * We initialize both the ParallelIndexScanDesc proper and the AM-specific
 * information which follows it.
 *
 * This function calls access method specific initialization routine to
 * initialize am specific information.  Call this just once in the leader
 * process; then, individual workers attach via index_beginscan_parallel.
 */
void
index_parallelscan_initialize(Relation heapRelation, Relation indexRelation,
                              Snapshot snapshot, ParallelIndexScanDesc target)
{
    Size        offset;
 
    Assert(snapshot != InvalidSnapshot);
 
    RELATION_CHECKS;
 
    offset = add_size(offsetof(ParallelIndexScanDescData, ps_snapshot_data),
                      EstimateSnapshotSpace(snapshot));
    offset = MAXALIGN(offset);
 
    target->ps_relid = RelationGetRelid(heapRelation);
    target->ps_indexid = RelationGetRelid(indexRelation);
    target->ps_offset = offset;
    SerializeSnapshot(snapshot, target->ps_snapshot_data);
 
    /* aminitparallelscan is optional; assume no-op if not provided by AM */
    if (indexRelation->rd_indam->aminitparallelscan != NULL)
    {
        void       *amtarget;
 
        amtarget = OffsetToPointer(target, offset);
        indexRelation->rd_indam->aminitparallelscan(amtarget);
    }
}
 
/* ----------------
 *      index_parallelrescan  - (re)start a parallel scan of an index
 * ----------------
 */
void
index_parallelrescan(IndexScanDesc scan)
{
    SCAN_CHECKS;
 
    if (scan->xs_heapfetch)
        table_index_fetch_reset(scan->xs_heapfetch);
 
    /* amparallelrescan is optional; assume no-op if not provided by AM */
    if (scan->indexRelation->rd_indam->amparallelrescan != NULL)
        scan->indexRelation->rd_indam->amparallelrescan(scan);
}
 
/*
 * index_beginscan_parallel - join parallel index scan
 *
 * Caller must be holding suitable locks on the heap and the index.
 */
IndexScanDesc
index_beginscan_parallel(Relation heaprel, Relation indexrel, int nkeys,
                         int norderbys, ParallelIndexScanDesc pscan)
{
    Snapshot    snapshot;
    IndexScanDesc scan;
 
    Assert(RelationGetRelid(heaprel) == pscan->ps_relid);
    snapshot = RestoreSnapshot(pscan->ps_snapshot_data);
    RegisterSnapshot(snapshot);
    scan = index_beginscan_internal(indexrel, nkeys, norderbys, snapshot,
                                    pscan, true);
 
    /*
     * Save additional parameters into the scandesc.  Everything else was set
     * up by index_beginscan_internal.
     */
    scan->heapRelation = heaprel;
    scan->xs_snapshot = snapshot;
 
    /* prepare to fetch index matches from table */
    scan->xs_heapfetch = table_index_fetch_begin(heaprel);
 
    return scan;
}
 
/* ----------------
 * index_getnext_tid - get the next TID from a scan
 *
 * The result is the next TID satisfying the scan keys,
 * or NULL if no more matching tuples exist.
 * ----------------
 */
ItemPointer
index_getnext_tid(IndexScanDesc scan, ScanDirection direction)
{
    bool        found;
 
    SCAN_CHECKS;
    CHECK_SCAN_PROCEDURE(amgettuple);
 
    /* XXX: we should assert that a snapshot is pushed or registered */
    Assert(TransactionIdIsValid(RecentXmin));
 
    /*
     * The AM's amgettuple proc finds the next index entry matching the scan
     * keys, and puts the TID into scan->xs_heaptid.  It should also set
     * scan->xs_recheck and possibly scan->xs_itup/scan->xs_hitup, though we
     * pay no attention to those fields here.
     */
    found = scan->indexRelation->rd_indam->amgettuple(scan, direction);
 
    /* Reset kill flag immediately for safety */
    scan->kill_prior_tuple = false;
    scan->xs_heap_continue = false;
 
    /* If we're out of index entries, we're done */
    if (!found)
    {
        /* release resources (like buffer pins) from table accesses */
        if (scan->xs_heapfetch)
            table_index_fetch_reset(scan->xs_heapfetch);
 
        return NULL;
    }
    Assert(ItemPointerIsValid(&scan->xs_heaptid));
 
    pgstat_count_index_tuples(scan->indexRelation, 1);
 
    /* Return the TID of the tuple we found. */
    return &scan->xs_heaptid;
}
 
/* ----------------
 *      index_fetch_heap - get the scan's next heap tuple
 *
 * The result is a visible heap tuple associated with the index TID most
 * recently fetched by index_getnext_tid, or NULL if no more matching tuples
 * exist.  (There can be more than one matching tuple because of HOT chains,
 * although when using an MVCC snapshot it should be impossible for more than
 * one such tuple to exist.)
 *
 * On success, the buffer containing the heap tup is pinned (the pin will be
 * dropped in a future index_getnext_tid, index_fetch_heap or index_endscan
 * call).
 *
 * Note: caller must check scan->xs_recheck, and perform rechecking of the
 * scan keys if required.  We do not do that here because we don't have
 * enough information to do it efficiently in the general case.
 * ----------------
 */
bool
index_fetch_heap(IndexScanDesc scan, TupleTableSlot *slot)
{
    bool        all_dead = false;
    bool        found;
 
    found = table_index_fetch_tuple(scan->xs_heapfetch, &scan->xs_heaptid,
                                    scan->xs_snapshot, slot,
                                    &scan->xs_heap_continue, &all_dead);
 
    if (found)
        pgstat_count_heap_fetch(scan->indexRelation);
 
    /*
     * If we scanned a whole HOT chain and found only dead tuples, tell index
     * AM to kill its entry for that TID (this will take effect in the next
     * amgettuple call, in index_getnext_tid).  We do not do this when in
     * recovery because it may violate MVCC to do so.  See comments in
     * RelationGetIndexScan().
     */
    if (!scan->xactStartedInRecovery)
        scan->kill_prior_tuple = all_dead;
 
    return found;
}
 
/* ----------------
 *      index_getnext_slot - get the next tuple from a scan
 *
 * The result is true if a tuple satisfying the scan keys and the snapshot was
 * found, false otherwise.  The tuple is stored in the specified slot.
 *
 * On success, resources (like buffer pins) are likely to be held, and will be
 * dropped by a future index_getnext_tid, index_fetch_heap or index_endscan
 * call).
 *
 * Note: caller must check scan->xs_recheck, and perform rechecking of the
 * scan keys if required.  We do not do that here because we don't have
 * enough information to do it efficiently in the general case.
 * ----------------
 */
bool
index_getnext_slot(IndexScanDesc scan, ScanDirection direction, TupleTableSlot *slot)
{
    for (;;)
    {
        if (!scan->xs_heap_continue)
        {
            ItemPointer tid;
 
            /* Time to fetch the next TID from the index */
            tid = index_getnext_tid(scan, direction);
 
            /* If we're out of index entries, we're done */
            if (tid == NULL)
                break;
 
            Assert(ItemPointerEquals(tid, &scan->xs_heaptid));
        }
 
        /*
         * Fetch the next (or only) visible heap tuple for this index entry.
         * If we don't find anything, loop around and grab the next TID from
         * the index.
         */
        Assert(ItemPointerIsValid(&scan->xs_heaptid));
        if (index_fetch_heap(scan, slot))
            return true;
    }
 
    return false;
}
 
/* ----------------
 *      index_getbitmap - get all tuples at once from an index scan
 *
 * Adds the TIDs of all heap tuples satisfying the scan keys to a bitmap.
 * Since there's no interlock between the index scan and the eventual heap
 * access, this is only safe to use with MVCC-based snapshots: the heap
 * item slot could have been replaced by a newer tuple by the time we get
 * to it.
 *
 * Returns the number of matching tuples found.  (Note: this might be only
 * approximate, so it should only be used for statistical purposes.)
 * ----------------
 */
int64
index_getbitmap(IndexScanDesc scan, TIDBitmap *bitmap)
{
    int64       ntids;
 
    SCAN_CHECKS;
    CHECK_SCAN_PROCEDURE(amgetbitmap);
 
    /* just make sure this is false... */
    scan->kill_prior_tuple = false;
 
    /*
     * have the am's getbitmap proc do all the work.
     */
    ntids = scan->indexRelation->rd_indam->amgetbitmap(scan, bitmap);
 
    pgstat_count_index_tuples(scan->indexRelation, ntids);
 
    return ntids;
}
 
/* ----------------
 *      index_bulk_delete - do mass deletion of index entries
 *
 *      callback routine tells whether a given main-heap tuple is
 *      to be deleted
 *
 *      return value is an optional palloc'd struct of statistics
 * ----------------
 */
IndexBulkDeleteResult *
index_bulk_delete(IndexVacuumInfo *info,
                  IndexBulkDeleteResult *istat,
                  IndexBulkDeleteCallback callback,
                  void *callback_state)
{
    Relation    indexRelation = info->index;
 
    RELATION_CHECKS;
    CHECK_REL_PROCEDURE(ambulkdelete);
 
    return indexRelation->rd_indam->ambulkdelete(info, istat,
                                                 callback, callback_state);
}
 
/* ----------------
 *      index_vacuum_cleanup - do post-deletion cleanup of an index
 *
 *      return value is an optional palloc'd struct of statistics
 * ----------------
 */
IndexBulkDeleteResult *
index_vacuum_cleanup(IndexVacuumInfo *info,
                     IndexBulkDeleteResult *istat)
{
    Relation    indexRelation = info->index;
 
    RELATION_CHECKS;
    CHECK_REL_PROCEDURE(amvacuumcleanup);
 
    return indexRelation->rd_indam->amvacuumcleanup(info, istat);
}
 
/* ----------------
 *      index_can_return
 *
 *      Does the index access method support index-only scans for the given
 *      column?
 * ----------------
 */
bool
index_can_return(Relation indexRelation, int attno)
{
    RELATION_CHECKS;
 
    /* amcanreturn is optional; assume false if not provided by AM */
    if (indexRelation->rd_indam->amcanreturn == NULL)
        return false;
 
    return indexRelation->rd_indam->amcanreturn(indexRelation, attno);
}
 
/* ----------------
 *      index_getprocid
 *
 *      Index access methods typically require support routines that are
 *      not directly the implementation of any WHERE-clause query operator
 *      and so cannot be kept in pg_amop.  Instead, such routines are kept
 *      in pg_amproc.  These registered procedure OIDs are assigned numbers
 *      according to a convention established by the access method.
 *      The general index code doesn't know anything about the routines
 *      involved; it just builds an ordered list of them for
 *      each attribute on which an index is defined.
 *
 *      As of Postgres 8.3, support routines within an operator family
 *      are further subdivided by the "left type" and "right type" of the
 *      query operator(s) that they support.  The "default" functions for a
 *      particular indexed attribute are those with both types equal to
 *      the index opclass' opcintype (note that this is subtly different
 *      from the indexed attribute's own type: it may be a binary-compatible
 *      type instead).  Only the default functions are stored in relcache
 *      entries --- access methods can use the syscache to look up non-default
 *      functions.
 *
 *      This routine returns the requested default procedure OID for a
 *      particular indexed attribute.
 * ----------------
 */
RegProcedure
index_getprocid(Relation irel,
                AttrNumber attnum,
                uint16 procnum)
{
    RegProcedure *loc;
    int         nproc;
    int         procindex;
 
    nproc = irel->rd_indam->amsupport;
 
    Assert(procnum > 0 && procnum <= (uint16) nproc);
 
    procindex = (nproc * (attnum - 1)) + (procnum - 1);
 
    loc = irel->rd_support;
 
    Assert(loc != NULL);
 
    return loc[procindex];
}
 
/* ----------------
 *      index_getprocinfo
 *
 *      This routine allows index AMs to keep fmgr lookup info for
 *      support procs in the relcache.  As above, only the "default"
 *      functions for any particular indexed attribute are cached.
 *
 * Note: the return value points into cached data that will be lost during
 * any relcache rebuild!  Therefore, either use the callinfo right away,
 * or save it only after having acquired some type of lock on the index rel.
 * ----------------
 */
FmgrInfo *
index_getprocinfo(Relation irel,
                  AttrNumber attnum,
                  uint16 procnum)
{
    FmgrInfo   *locinfo;
    int         nproc;
    int         optsproc;
    int         procindex;
 
    nproc = irel->rd_indam->amsupport;
    optsproc = irel->rd_indam->amoptsprocnum;
 
    Assert(procnum > 0 && procnum <= (uint16) nproc);
 
    procindex = (nproc * (attnum - 1)) + (procnum - 1);
 
    locinfo = irel->rd_supportinfo;
 
    Assert(locinfo != NULL);
 
    locinfo += procindex;
 
    /* Initialize the lookup info if first time through */
    if (locinfo->fn_oid == InvalidOid)
    {
        RegProcedure *loc = irel->rd_support;
        RegProcedure procId;
 
        Assert(loc != NULL);
 
        procId = loc[procindex];
 
        /*
         * Complain if function was not found during IndexSupportInitialize.
         * This should not happen unless the system tables contain bogus
         * entries for the index opclass.  (If an AM wants to allow a support
         * function to be optional, it can use index_getprocid.)
         */
        if (!RegProcedureIsValid(procId))
            elog(ERROR, "missing support function %d for attribute %d of index \"%s\"",
                 procnum, attnum, RelationGetRelationName(irel));
 
        fmgr_info_cxt(procId, locinfo, irel->rd_indexcxt);
 
        if (procnum != optsproc)
        {
            /* Initialize locinfo->fn_expr with opclass options Const */
            bytea     **attoptions = RelationGetIndexAttOptions(irel, false);
            MemoryContext oldcxt = MemoryContextSwitchTo(irel->rd_indexcxt);
 
            set_fn_opclass_options(locinfo, attoptions[attnum - 1]);
 
            MemoryContextSwitchTo(oldcxt);
        }
    }
 
    return locinfo;
}
 
/* ----------------
 *      index_store_float8_orderby_distances
 *
 *      Convert AM distance function's results (that can be inexact)
 *      to ORDER BY types and save them into xs_orderbyvals/xs_orderbynulls
 *      for a possible recheck.
 * ----------------
 */
void
index_store_float8_orderby_distances(IndexScanDesc scan, Oid *orderByTypes,
                                     IndexOrderByDistance *distances,
                                     bool recheckOrderBy)
{
    int         i;
 
    Assert(distances || !recheckOrderBy);
 
    scan->xs_recheckorderby = recheckOrderBy;
 
    for (i = 0; i < scan->numberOfOrderBys; i++)
    {
        if (orderByTypes[i] == FLOAT8OID)
        {
#ifndef USE_FLOAT8_BYVAL
            /* must free any old value to avoid memory leakage */
            if (!scan->xs_orderbynulls[i])
                pfree(DatumGetPointer(scan->xs_orderbyvals[i]));
#endif
            if (distances && !distances[i].isnull)
            {
                scan->xs_orderbyvals[i] = Float8GetDatum(distances[i].value);
                scan->xs_orderbynulls[i] = false;
            }
            else
            {
                scan->xs_orderbyvals[i] = (Datum) 0;
                scan->xs_orderbynulls[i] = true;
            }
        }
        else if (orderByTypes[i] == FLOAT4OID)
        {
            /* convert distance function's result to ORDER BY type */
            if (distances && !distances[i].isnull)
            {
                scan->xs_orderbyvals[i] = Float4GetDatum((float4) distances[i].value);
                scan->xs_orderbynulls[i] = false;
            }
            else
            {
                scan->xs_orderbyvals[i] = (Datum) 0;
                scan->xs_orderbynulls[i] = true;
            }
        }
        else
        {
            /*
             * If the ordering operator's return value is anything else, we
             * don't know how to convert the float8 bound calculated by the
             * distance function to that.  The executor won't actually need
             * the order by values we return here, if there are no lossy
             * results, so only insist on converting if the *recheck flag is
             * set.
             */
            if (scan->xs_recheckorderby)
                elog(ERROR, "ORDER BY operator must return float8 or float4 if the distance function is lossy");
            scan->xs_orderbynulls[i] = true;
        }
    }
}
 
/* ----------------
 *      index_opclass_options
 *
 *      Parse opclass-specific options for index column.
 * ----------------
 */
bytea *
index_opclass_options(Relation indrel, AttrNumber attnum, Datum attoptions,
                      bool validate)
{
    int         amoptsprocnum = indrel->rd_indam->amoptsprocnum;
    Oid         procid = InvalidOid;
    FmgrInfo   *procinfo;
    local_relopts relopts;
 
    /* fetch options support procedure if specified */
    if (amoptsprocnum != 0)
        procid = index_getprocid(indrel, attnum, amoptsprocnum);
 
    if (!OidIsValid(procid))
    {
        Oid         opclass;
        Datum       indclassDatum;
        oidvector  *indclass;
 
        if (!DatumGetPointer(attoptions))
            return NULL;        /* ok, no options, no procedure */
 
        /*
         * Report an error if the opclass's options-parsing procedure does not
         * exist but the opclass options are specified.
         */
        indclassDatum = SysCacheGetAttrNotNull(INDEXRELID, indrel->rd_indextuple,
                                               Anum_pg_index_indclass);
        indclass = (oidvector *) DatumGetPointer(indclassDatum);
        opclass = indclass->values[attnum - 1];
 
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("operator class %s has no options",
                        generate_opclass_name(opclass))));
    }
 
    init_local_reloptions(&relopts, 0);
 
    procinfo = index_getprocinfo(indrel, attnum, amoptsprocnum);
 
    (void) FunctionCall1(procinfo, PointerGetDatum(&relopts));
 
    return build_local_reloptions(&relopts, attoptions, validate);
}