[pg-rex/syncrep.git] / src / backend / access / nbtree / nbtutils.c

/*-------------------------------------------------------------------------
 *
 * nbtutils.c
 *        Utility code for Postgres btree implementation.
 *
 * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *        src/backend/access/nbtree/nbtutils.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <time.h>

#include "access/genam.h"
#include "access/nbtree.h"
#include "access/reloptions.h"
#include "access/relscan.h"
#include "executor/execdebug.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "storage/lwlock.h"
#include "storage/shmem.h"
#include "utils/lsyscache.h"


static bool _bt_compare_scankey_args(IndexScanDesc scan, ScanKey op,
                                                 ScanKey leftarg, ScanKey rightarg,
                                                 bool *result);
static bool _bt_fix_scankey_strategy(ScanKey skey, int16 *indoption);
static void _bt_mark_scankey_required(ScanKey skey);
static bool _bt_check_rowcompare(ScanKey skey,
                                         IndexTuple tuple, TupleDesc tupdesc,
                                         ScanDirection dir, bool *continuescan);


/*
 * _bt_mkscankey
 *              Build an insertion scan key that contains comparison data from itup
 *              as well as comparator routines appropriate to the key datatypes.
 *
 *              The result is intended for use with _bt_compare().
 */
ScanKey
_bt_mkscankey(Relation rel, IndexTuple itup)
{
        ScanKey         skey;
        TupleDesc       itupdesc;
        int                     natts;
        int16      *indoption;
        int                     i;

        itupdesc = RelationGetDescr(rel);
        natts = RelationGetNumberOfAttributes(rel);
        indoption = rel->rd_indoption;

        skey = (ScanKey) palloc(natts * sizeof(ScanKeyData));

        for (i = 0; i < natts; i++)
        {
                FmgrInfo   *procinfo;
                Datum           arg;
                bool            null;
                int                     flags;

                /*
                 * We can use the cached (default) support procs since no cross-type
                 * comparison can be needed.
                 */
                procinfo = index_getprocinfo(rel, i + 1, BTORDER_PROC);
                arg = index_getattr(itup, i + 1, itupdesc, &null);
                flags = (null ? SK_ISNULL : 0) | (indoption[i] << SK_BT_INDOPTION_SHIFT);
                ScanKeyEntryInitializeWithInfo(&skey[i],
                                                                           flags,
                                                                           (AttrNumber) (i + 1),
                                                                           InvalidStrategy,
                                                                           InvalidOid,
                                                                           rel->rd_indcollation[i],
                                                                           procinfo,
                                                                           arg);
        }

        return skey;
}

/*
 * _bt_mkscankey_nodata
 *              Build an insertion scan key that contains 3-way comparator routines
 *              appropriate to the key datatypes, but no comparison data.  The
 *              comparison data ultimately used must match the key datatypes.
 *
 *              The result cannot be used with _bt_compare(), unless comparison
 *              data is first stored into the key entries.      Currently this
 *              routine is only called by nbtsort.c and tuplesort.c, which have
 *              their own comparison routines.
 */
ScanKey
_bt_mkscankey_nodata(Relation rel)
{
        ScanKey         skey;
        int                     natts;
        int16      *indoption;
        int                     i;

        natts = RelationGetNumberOfAttributes(rel);
        indoption = rel->rd_indoption;

        skey = (ScanKey) palloc(natts * sizeof(ScanKeyData));

        for (i = 0; i < natts; i++)
        {
                FmgrInfo   *procinfo;
                int                     flags;

                /*
                 * We can use the cached (default) support procs since no cross-type
                 * comparison can be needed.
                 */
                procinfo = index_getprocinfo(rel, i + 1, BTORDER_PROC);
                flags = SK_ISNULL | (indoption[i] << SK_BT_INDOPTION_SHIFT);
                ScanKeyEntryInitializeWithInfo(&skey[i],
                                                                           flags,
                                                                           (AttrNumber) (i + 1),
                                                                           InvalidStrategy,
                                                                           InvalidOid,
                                                                           rel->rd_indcollation[i],
                                                                           procinfo,
                                                                           (Datum) 0);
        }

        return skey;
}

/*
 * free a scan key made by either _bt_mkscankey or _bt_mkscankey_nodata.
 */
void
_bt_freeskey(ScanKey skey)
{
        pfree(skey);
}

/*
 * free a retracement stack made by _bt_search.
 */
void
_bt_freestack(BTStack stack)
{
        BTStack         ostack;

        while (stack != NULL)
        {
                ostack = stack;
                stack = stack->bts_parent;
                pfree(ostack);
        }
}


/*
 *      _bt_preprocess_keys() -- Preprocess scan keys
 *
 * The caller-supplied search-type keys (in scan->keyData[]) are copied to
 * so->keyData[] with possible transformation.  scan->numberOfKeys is
 * the number of input keys, so->numberOfKeys gets the number of output
 * keys (possibly less, never greater).
 *
 * The output keys are marked with additional sk_flag bits beyond the
 * system-standard bits supplied by the caller.  The DESC and NULLS_FIRST
 * indoption bits for the relevant index attribute are copied into the flags.
 * Also, for a DESC column, we commute (flip) all the sk_strategy numbers
 * so that the index sorts in the desired direction.
 *
 * One key purpose of this routine is to discover how many scan keys
 * must be satisfied to continue the scan.      It also attempts to eliminate
 * redundant keys and detect contradictory keys.  (If the index opfamily
 * provides incomplete sets of cross-type operators, we may fail to detect
 * redundant or contradictory keys, but we can survive that.)
 *
 * The output keys must be sorted by index attribute.  Presently we expect
 * (but verify) that the input keys are already so sorted --- this is done
 * by group_clauses_by_indexkey() in indxpath.c.  Some reordering of the keys
 * within each attribute may be done as a byproduct of the processing here,
 * but no other code depends on that.
 *
 * The output keys are marked with flags SK_BT_REQFWD and/or SK_BT_REQBKWD
 * if they must be satisfied in order to continue the scan forward or backward
 * respectively.  _bt_checkkeys uses these flags.  For example, if the quals
 * are "x = 1 AND y < 4 AND z < 5", then _bt_checkkeys will reject a tuple
 * (1,2,7), but we must continue the scan in case there are tuples (1,3,z).
 * But once we reach tuples like (1,4,z) we can stop scanning because no
 * later tuples could match.  This is reflected by marking the x and y keys,
 * but not the z key, with SK_BT_REQFWD.  In general, the keys for leading
 * attributes with "=" keys are marked both SK_BT_REQFWD and SK_BT_REQBKWD.
 * For the first attribute without an "=" key, any "<" and "<=" keys are
 * marked SK_BT_REQFWD while any ">" and ">=" keys are marked SK_BT_REQBKWD.
 * This can be seen to be correct by considering the above example.  Note
 * in particular that if there are no keys for a given attribute, the keys for
 * subsequent attributes can never be required; for instance "WHERE y = 4"
 * requires a full-index scan.
 *
 * If possible, redundant keys are eliminated: we keep only the tightest
 * >/>= bound and the tightest </<= bound, and if there's an = key then
 * that's the only one returned.  (So, we return either a single = key,
 * or one or two boundary-condition keys for each attr.)  However, if we
 * cannot compare two keys for lack of a suitable cross-type operator,
 * we cannot eliminate either.  If there are two such keys of the same
 * operator strategy, the second one is just pushed into the output array
 * without further processing here.  We may also emit both >/>= or both
 * </<= keys if we can't compare them.  The logic about required keys still
 * works if we don't eliminate redundant keys.
 *
 * As a byproduct of this work, we can detect contradictory quals such
 * as "x = 1 AND x > 2".  If we see that, we return so->qual_ok = FALSE,
 * indicating the scan need not be run at all since no tuples can match.
 * (In this case we do not bother completing the output key array!)
 * Again, missing cross-type operators might cause us to fail to prove the
 * quals contradictory when they really are, but the scan will work correctly.
 *
 * Row comparison keys are currently also treated without any smarts:
 * we just transfer them into the preprocessed array without any
 * editorialization.  We can treat them the same as an ordinary inequality
 * comparison on the row's first index column, for the purposes of the logic
 * about required keys.
 *
 * Note: the reason we have to copy the preprocessed scan keys into private
 * storage is that we are modifying the array based on comparisons of the
 * key argument values, which could change on a rescan.  Therefore we can't
 * overwrite the caller's data structure.
 */
void
_bt_preprocess_keys(IndexScanDesc scan)
{
        BTScanOpaque so = (BTScanOpaque) scan->opaque;
        int                     numberOfKeys = scan->numberOfKeys;
        int16      *indoption = scan->indexRelation->rd_indoption;
        int                     new_numberOfKeys;
        int                     numberOfEqualCols;
        ScanKey         inkeys;
        ScanKey         outkeys;
        ScanKey         cur;
        ScanKey         xform[BTMaxStrategyNumber];
        bool            test_result;
        int                     i,
                                j;
        AttrNumber      attno;

        /* initialize result variables */
        so->qual_ok = true;
        so->numberOfKeys = 0;

        if (numberOfKeys < 1)
                return;                                 /* done if qual-less scan */

        inkeys = scan->keyData;
        outkeys = so->keyData;
        cur = &inkeys[0];
        /* we check that input keys are correctly ordered */
        if (cur->sk_attno < 1)
                elog(ERROR, "btree index keys must be ordered by attribute");

        /* We can short-circuit most of the work if there's just one key */
        if (numberOfKeys == 1)
        {
                /* Apply indoption to scankey (might change sk_strategy!) */
                if (!_bt_fix_scankey_strategy(cur, indoption))
                        so->qual_ok = false;
                memcpy(outkeys, cur, sizeof(ScanKeyData));
                so->numberOfKeys = 1;
                /* We can mark the qual as required if it's for first index col */
                if (cur->sk_attno == 1)
                        _bt_mark_scankey_required(outkeys);
                return;
        }

        /*
         * Otherwise, do the full set of pushups.
         */
        new_numberOfKeys = 0;
        numberOfEqualCols = 0;

        /*
         * Initialize for processing of keys for attr 1.
         *
         * xform[i] points to the currently best scan key of strategy type i+1; it
         * is NULL if we haven't yet found such a key for this attr.
         */
        attno = 1;
        memset(xform, 0, sizeof(xform));

        /*
         * Loop iterates from 0 to numberOfKeys inclusive; we use the last pass to
         * handle after-last-key processing.  Actual exit from the loop is at the
         * "break" statement below.
         */
        for (i = 0;; cur++, i++)
        {
                if (i < numberOfKeys)
                {
                        /* Apply indoption to scankey (might change sk_strategy!) */
                        if (!_bt_fix_scankey_strategy(cur, indoption))
                        {
                                /* NULL can't be matched, so give up */
                                so->qual_ok = false;
                                return;
                        }
                }

                /*
                 * If we are at the end of the keys for a particular attr, finish up
                 * processing and emit the cleaned-up keys.
                 */
                if (i == numberOfKeys || cur->sk_attno != attno)
                {
                        int                     priorNumberOfEqualCols = numberOfEqualCols;

                        /* check input keys are correctly ordered */
                        if (i < numberOfKeys && cur->sk_attno < attno)
                                elog(ERROR, "btree index keys must be ordered by attribute");

                        /*
                         * If = has been specified, all other keys can be eliminated as
                         * redundant.  If we have a case like key = 1 AND key > 2, we can
                         * set qual_ok to false and abandon further processing.
                         *
                         * We also have to deal with the case of "key IS NULL", which is
                         * unsatisfiable in combination with any other index condition.
                         * By the time we get here, that's been classified as an equality
                         * check, and we've rejected any combination of it with a regular
                         * equality condition; but not with other types of conditions.
                         */
                        if (xform[BTEqualStrategyNumber - 1])
                        {
                                ScanKey         eq = xform[BTEqualStrategyNumber - 1];

                                for (j = BTMaxStrategyNumber; --j >= 0;)
                                {
                                        ScanKey         chk = xform[j];

                                        if (!chk || j == (BTEqualStrategyNumber - 1))
                                                continue;

                                        if (eq->sk_flags & SK_SEARCHNULL)
                                        {
                                                /* IS NULL is contradictory to anything else */
                                                so->qual_ok = false;
                                                return;
                                        }

                                        if (_bt_compare_scankey_args(scan, chk, eq, chk,
                                                                                                 &test_result))
                                        {
                                                if (!test_result)
                                                {
                                                        /* keys proven mutually contradictory */
                                                        so->qual_ok = false;
                                                        return;
                                                }
                                                /* else discard the redundant non-equality key */
                                                xform[j] = NULL;
                                        }
                                        /* else, cannot determine redundancy, keep both keys */
                                }
                                /* track number of attrs for which we have "=" keys */
                                numberOfEqualCols++;
                        }

                        /* try to keep only one of <, <= */
                        if (xform[BTLessStrategyNumber - 1]
                                && xform[BTLessEqualStrategyNumber - 1])
                        {
                                ScanKey         lt = xform[BTLessStrategyNumber - 1];
                                ScanKey         le = xform[BTLessEqualStrategyNumber - 1];

                                if (_bt_compare_scankey_args(scan, le, lt, le,
                                                                                         &test_result))
                                {
                                        if (test_result)
                                                xform[BTLessEqualStrategyNumber - 1] = NULL;
                                        else
                                                xform[BTLessStrategyNumber - 1] = NULL;
                                }
                        }

                        /* try to keep only one of >, >= */
                        if (xform[BTGreaterStrategyNumber - 1]
                                && xform[BTGreaterEqualStrategyNumber - 1])
                        {
                                ScanKey         gt = xform[BTGreaterStrategyNumber - 1];
                                ScanKey         ge = xform[BTGreaterEqualStrategyNumber - 1];

                                if (_bt_compare_scankey_args(scan, ge, gt, ge,
                                                                                         &test_result))
                                {
                                        if (test_result)
                                                xform[BTGreaterEqualStrategyNumber - 1] = NULL;
                                        else
                                                xform[BTGreaterStrategyNumber - 1] = NULL;
                                }
                        }

                        /*
                         * Emit the cleaned-up keys into the outkeys[] array, and then
                         * mark them if they are required.      They are required (possibly
                         * only in one direction) if all attrs before this one had "=".
                         */
                        for (j = BTMaxStrategyNumber; --j >= 0;)
                        {
                                if (xform[j])
                                {
                                        ScanKey         outkey = &outkeys[new_numberOfKeys++];

                                        memcpy(outkey, xform[j], sizeof(ScanKeyData));
                                        if (priorNumberOfEqualCols == attno - 1)
                                                _bt_mark_scankey_required(outkey);
                                }
                        }

                        /*
                         * Exit loop here if done.
                         */
                        if (i == numberOfKeys)
                                break;

                        /* Re-initialize for new attno */
                        attno = cur->sk_attno;
                        memset(xform, 0, sizeof(xform));
                }

                /* check strategy this key's operator corresponds to */
                j = cur->sk_strategy - 1;

                /* if row comparison, push it directly to the output array */
                if (cur->sk_flags & SK_ROW_HEADER)
                {
                        ScanKey         outkey = &outkeys[new_numberOfKeys++];

                        memcpy(outkey, cur, sizeof(ScanKeyData));
                        if (numberOfEqualCols == attno - 1)
                                _bt_mark_scankey_required(outkey);

                        /*
                         * We don't support RowCompare using equality; such a qual would
                         * mess up the numberOfEqualCols tracking.
                         */
                        Assert(j != (BTEqualStrategyNumber - 1));
                        continue;
                }

                /* have we seen one of these before? */
                if (xform[j] == NULL)
                {
                        /* nope, so remember this scankey */
                        xform[j] = cur;
                }
                else
                {
                        /* yup, keep only the more restrictive key */
                        if (_bt_compare_scankey_args(scan, cur, cur, xform[j],
                                                                                 &test_result))
                        {
                                if (test_result)
                                        xform[j] = cur;
                                else if (j == (BTEqualStrategyNumber - 1))
                                {
                                        /* key == a && key == b, but a != b */
                                        so->qual_ok = false;
                                        return;
                                }
                                /* else old key is more restrictive, keep it */
                        }
                        else
                        {
                                /*
                                 * We can't determine which key is more restrictive.  Keep the
                                 * previous one in xform[j] and push this one directly to the
                                 * output array.
                                 */
                                ScanKey         outkey = &outkeys[new_numberOfKeys++];

                                memcpy(outkey, cur, sizeof(ScanKeyData));
                                if (numberOfEqualCols == attno - 1)
                                        _bt_mark_scankey_required(outkey);
                        }
                }
        }

        so->numberOfKeys = new_numberOfKeys;
}

/*
 * Compare two scankey values using a specified operator.
 *
 * The test we want to perform is logically "leftarg op rightarg", where
 * leftarg and rightarg are the sk_argument values in those ScanKeys, and
 * the comparison operator is the one in the op ScanKey.  However, in
 * cross-data-type situations we may need to look up the correct operator in
 * the index's opfamily: it is the one having amopstrategy = op->sk_strategy
 * and amoplefttype/amoprighttype equal to the two argument datatypes.
 *
 * If the opfamily doesn't supply a complete set of cross-type operators we
 * may not be able to make the comparison.      If we can make the comparison
 * we store the operator result in *result and return TRUE.  We return FALSE
 * if the comparison could not be made.
 *
 * Note: op always points at the same ScanKey as either leftarg or rightarg.
 * Since we don't scribble on the scankeys, this aliasing should cause no
 * trouble.
 *
 * Note: this routine needs to be insensitive to any DESC option applied
 * to the index column.  For example, "x < 4" is a tighter constraint than
 * "x < 5" regardless of which way the index is sorted.
 */
static bool
_bt_compare_scankey_args(IndexScanDesc scan, ScanKey op,
                                                 ScanKey leftarg, ScanKey rightarg,
                                                 bool *result)
{
        Relation        rel = scan->indexRelation;
        Oid                     lefttype,
                                righttype,
                                optype,
                                opcintype,
                                cmp_op;
        StrategyNumber strat;

        /*
         * First, deal with cases where one or both args are NULL.      This should
         * only happen when the scankeys represent IS NULL/NOT NULL conditions.
         */
        if ((leftarg->sk_flags | rightarg->sk_flags) & SK_ISNULL)
        {
                bool            leftnull,
                                        rightnull;

                if (leftarg->sk_flags & SK_ISNULL)
                {
                        Assert(leftarg->sk_flags & (SK_SEARCHNULL | SK_SEARCHNOTNULL));
                        leftnull = true;
                }
                else
                        leftnull = false;
                if (rightarg->sk_flags & SK_ISNULL)
                {
                        Assert(rightarg->sk_flags & (SK_SEARCHNULL | SK_SEARCHNOTNULL));
                        rightnull = true;
                }
                else
                        rightnull = false;

                /*
                 * We treat NULL as either greater than or less than all other values.
                 * Since true > false, the tests below work correctly for NULLS LAST
                 * logic.  If the index is NULLS FIRST, we need to flip the strategy.
                 */
                strat = op->sk_strategy;
                if (op->sk_flags & SK_BT_NULLS_FIRST)
                        strat = BTCommuteStrategyNumber(strat);

                switch (strat)
                {
                        case BTLessStrategyNumber:
                                *result = (leftnull < rightnull);
                                break;
                        case BTLessEqualStrategyNumber:
                                *result = (leftnull <= rightnull);
                                break;
                        case BTEqualStrategyNumber:
                                *result = (leftnull == rightnull);
                                break;
                        case BTGreaterEqualStrategyNumber:
                                *result = (leftnull >= rightnull);
                                break;
                        case BTGreaterStrategyNumber:
                                *result = (leftnull > rightnull);
                                break;
                        default:
                                elog(ERROR, "unrecognized StrategyNumber: %d", (int) strat);
                                *result = false;        /* keep compiler quiet */
                                break;
                }
                return true;
        }

        /*
         * The opfamily we need to worry about is identified by the index column.
         */
        Assert(leftarg->sk_attno == rightarg->sk_attno);

        opcintype = rel->rd_opcintype[leftarg->sk_attno - 1];

        /*
         * Determine the actual datatypes of the ScanKey arguments.  We have to
         * support the convention that sk_subtype == InvalidOid means the opclass
         * input type; this is a hack to simplify life for ScanKeyInit().
         */
        lefttype = leftarg->sk_subtype;
        if (lefttype == InvalidOid)
                lefttype = opcintype;
        righttype = rightarg->sk_subtype;
        if (righttype == InvalidOid)
                righttype = opcintype;
        optype = op->sk_subtype;
        if (optype == InvalidOid)
                optype = opcintype;

        /*
         * If leftarg and rightarg match the types expected for the "op" scankey,
         * we can use its already-looked-up comparison function.
         */
        if (lefttype == opcintype && righttype == optype)
        {
                *result = DatumGetBool(FunctionCall2Coll(&op->sk_func,
                                                                                                 op->sk_collation,
                                                                                                 leftarg->sk_argument,
                                                                                                 rightarg->sk_argument));
                return true;
        }

        /*
         * Otherwise, we need to go to the syscache to find the appropriate
         * operator.  (This cannot result in infinite recursion, since no
         * indexscan initiated by syscache lookup will use cross-data-type
         * operators.)
         *
         * If the sk_strategy was flipped by _bt_fix_scankey_strategy, we have to
         * un-flip it to get the correct opfamily member.
         */
        strat = op->sk_strategy;
        if (op->sk_flags & SK_BT_DESC)
                strat = BTCommuteStrategyNumber(strat);

        cmp_op = get_opfamily_member(rel->rd_opfamily[leftarg->sk_attno - 1],
                                                                 lefttype,
                                                                 righttype,
                                                                 strat);
        if (OidIsValid(cmp_op))
        {
                RegProcedure cmp_proc = get_opcode(cmp_op);

                if (RegProcedureIsValid(cmp_proc))
                {
                        *result = DatumGetBool(OidFunctionCall2Coll(cmp_proc,
                                                                                                                op->sk_collation,
                                                                                                                leftarg->sk_argument,
                                                                                                         rightarg->sk_argument));
                        return true;
                }
        }

        /* Can't make the comparison */
        *result = false;                        /* suppress compiler warnings */
        return false;
}

/*
 * Adjust a scankey's strategy and flags setting as needed for indoptions.
 *
 * We copy the appropriate indoption value into the scankey sk_flags
 * (shifting to avoid clobbering system-defined flag bits).  Also, if
 * the DESC option is set, commute (flip) the operator strategy number.
 *
 * A secondary purpose is to check for IS NULL/NOT NULL scankeys and set up
 * the strategy field correctly for them.
 *
 * Lastly, for ordinary scankeys (not IS NULL/NOT NULL), we check for a
 * NULL comparison value.  Since all btree operators are assumed strict,
 * a NULL means that the qual cannot be satisfied.      We return TRUE if the
 * comparison value isn't NULL, or FALSE if the scan should be abandoned.
 *
 * This function is applied to the *input* scankey structure; therefore
 * on a rescan we will be looking at already-processed scankeys.  Hence
 * we have to be careful not to re-commute the strategy if we already did it.
 * It's a bit ugly to modify the caller's copy of the scankey but in practice
 * there shouldn't be any problem, since the index's indoptions are certainly
 * not going to change while the scankey survives.
 */
static bool
_bt_fix_scankey_strategy(ScanKey skey, int16 *indoption)
{
        int                     addflags;

        addflags = indoption[skey->sk_attno - 1] << SK_BT_INDOPTION_SHIFT;

        /*
         * We treat all btree operators as strict (even if they're not so marked
         * in pg_proc). This means that it is impossible for an operator condition
         * with a NULL comparison constant to succeed, and we can reject it right
         * away.
         *
         * However, we now also support "x IS NULL" clauses as search conditions,
         * so in that case keep going. The planner has not filled in any
         * particular strategy in this case, so set it to BTEqualStrategyNumber
         * --- we can treat IS NULL as an equality operator for purposes of search
         * strategy.
         *
         * Likewise, "x IS NOT NULL" is supported.      We treat that as either "less
         * than NULL" in a NULLS LAST index, or "greater than NULL" in a NULLS
         * FIRST index.
         *
         * Note: someday we might have to fill in sk_collation from the index
         * column's collation.  At the moment this is a non-issue because we'll
         * never actually call the comparison operator on a NULL.
         */
        if (skey->sk_flags & SK_ISNULL)
        {
                /* SK_ISNULL shouldn't be set in a row header scankey */
                Assert(!(skey->sk_flags & SK_ROW_HEADER));

                /* Set indoption flags in scankey (might be done already) */
                skey->sk_flags |= addflags;

                /* Set correct strategy for IS NULL or NOT NULL search */
                if (skey->sk_flags & SK_SEARCHNULL)
                {
                        skey->sk_strategy = BTEqualStrategyNumber;
                        skey->sk_subtype = InvalidOid;
                        skey->sk_collation = InvalidOid;
                }
                else if (skey->sk_flags & SK_SEARCHNOTNULL)
                {
                        if (skey->sk_flags & SK_BT_NULLS_FIRST)
                                skey->sk_strategy = BTGreaterStrategyNumber;
                        else
                                skey->sk_strategy = BTLessStrategyNumber;
                        skey->sk_subtype = InvalidOid;
                        skey->sk_collation = InvalidOid;
                }
                else
                {
                        /* regular qual, so it cannot be satisfied */
                        return false;
                }

                /* Needn't do the rest */
                return true;
        }

        /* Adjust strategy for DESC, if we didn't already */
        if ((addflags & SK_BT_DESC) && !(skey->sk_flags & SK_BT_DESC))
                skey->sk_strategy = BTCommuteStrategyNumber(skey->sk_strategy);
        skey->sk_flags |= addflags;

        /* If it's a row header, fix row member flags and strategies similarly */
        if (skey->sk_flags & SK_ROW_HEADER)
        {
                ScanKey         subkey = (ScanKey) DatumGetPointer(skey->sk_argument);

                for (;;)
                {
                        Assert(subkey->sk_flags & SK_ROW_MEMBER);
                        addflags = indoption[subkey->sk_attno - 1] << SK_BT_INDOPTION_SHIFT;
                        if ((addflags & SK_BT_DESC) && !(subkey->sk_flags & SK_BT_DESC))
                                subkey->sk_strategy = BTCommuteStrategyNumber(subkey->sk_strategy);
                        subkey->sk_flags |= addflags;
                        if (subkey->sk_flags & SK_ROW_END)
                                break;
                        subkey++;
                }
        }

        return true;
}

/*
 * Mark a scankey as "required to continue the scan".
 *
 * Depending on the operator type, the key may be required for both scan
 * directions or just one.      Also, if the key is a row comparison header,
 * we have to mark the appropriate subsidiary ScanKeys as required.  In
 * such cases, the first subsidiary key is required, but subsequent ones
 * are required only as long as they correspond to successive index columns
 * and match the leading column as to sort direction.
 * Otherwise the row comparison ordering is different from the index ordering
 * and so we can't stop the scan on the basis of those lower-order columns.
 *
 * Note: when we set required-key flag bits in a subsidiary scankey, we are
 * scribbling on a data structure belonging to the index AM's caller, not on
 * our private copy.  This should be OK because the marking will not change
 * from scan to scan within a query, and so we'd just re-mark the same way
 * anyway on a rescan.  Something to keep an eye on though.
 */
static void
_bt_mark_scankey_required(ScanKey skey)
{
        int                     addflags;

        switch (skey->sk_strategy)
        {
                case BTLessStrategyNumber:
                case BTLessEqualStrategyNumber:
                        addflags = SK_BT_REQFWD;
                        break;
                case BTEqualStrategyNumber:
                        addflags = SK_BT_REQFWD | SK_BT_REQBKWD;
                        break;
                case BTGreaterEqualStrategyNumber:
                case BTGreaterStrategyNumber:
                        addflags = SK_BT_REQBKWD;
                        break;
                default:
                        elog(ERROR, "unrecognized StrategyNumber: %d",
                                 (int) skey->sk_strategy);
                        addflags = 0;           /* keep compiler quiet */
                        break;
        }

        skey->sk_flags |= addflags;

        if (skey->sk_flags & SK_ROW_HEADER)
        {
                ScanKey         subkey = (ScanKey) DatumGetPointer(skey->sk_argument);
                AttrNumber      attno = skey->sk_attno;

                /* First subkey should be same as the header says */
                Assert(subkey->sk_attno == attno);

                for (;;)
                {
                        Assert(subkey->sk_flags & SK_ROW_MEMBER);
                        if (subkey->sk_attno != attno)
                                break;                  /* non-adjacent key, so not required */
                        if (subkey->sk_strategy != skey->sk_strategy)
                                break;                  /* wrong direction, so not required */
                        subkey->sk_flags |= addflags;
                        if (subkey->sk_flags & SK_ROW_END)
                                break;
                        subkey++;
                        attno++;
                }
        }
}

/*
 * Test whether an indextuple satisfies all the scankey conditions.
 *
 * If so, copy its TID into scan->xs_ctup.t_self, and return TRUE.
 * If not, return FALSE (xs_ctup is not changed).
 *
 * If the tuple fails to pass the qual, we also determine whether there's
 * any need to continue the scan beyond this tuple, and set *continuescan
 * accordingly.  See comments for _bt_preprocess_keys(), above, about how
 * this is done.
 *
 * scan: index scan descriptor (containing a search-type scankey)
 * page: buffer page containing index tuple
 * offnum: offset number of index tuple (must be a valid item!)
 * dir: direction we are scanning in
 * continuescan: output parameter (will be set correctly in all cases)
 */
bool
_bt_checkkeys(IndexScanDesc scan,
                          Page page, OffsetNumber offnum,
                          ScanDirection dir, bool *continuescan)
{
        ItemId          iid = PageGetItemId(page, offnum);
        bool            tuple_valid;
        IndexTuple      tuple;
        TupleDesc       tupdesc;
        BTScanOpaque so;
        int                     keysz;
        int                     ikey;
        ScanKey         key;

        *continuescan = true;           /* default assumption */

        /*
         * If the scan specifies not to return killed tuples, then we treat a
         * killed tuple as not passing the qual.  Most of the time, it's a win to
         * not bother examining the tuple's index keys, but just return
         * immediately with continuescan = true to proceed to the next tuple.
         * However, if this is the last tuple on the page, we should check the
         * index keys to prevent uselessly advancing to the next page.
         */
        if (scan->ignore_killed_tuples && ItemIdIsDead(iid))
        {
                /* return immediately if there are more tuples on the page */
                if (ScanDirectionIsForward(dir))
                {
                        if (offnum < PageGetMaxOffsetNumber(page))
                                return false;
                }
                else
                {
                        BTPageOpaque opaque = (BTPageOpaque) PageGetSpecialPointer(page);

                        if (offnum > P_FIRSTDATAKEY(opaque))
                                return false;
                }

                /*
                 * OK, we want to check the keys, but we'll return FALSE even if the
                 * tuple passes the key tests.
                 */
                tuple_valid = false;
        }
        else
                tuple_valid = true;

        tuple = (IndexTuple) PageGetItem(page, iid);

        tupdesc = RelationGetDescr(scan->indexRelation);
        so = (BTScanOpaque) scan->opaque;
        keysz = so->numberOfKeys;

        for (key = so->keyData, ikey = 0; ikey < keysz; key++, ikey++)
        {
                Datum           datum;
                bool            isNull;
                Datum           test;

                /* row-comparison keys need special processing */
                if (key->sk_flags & SK_ROW_HEADER)
                {
                        if (_bt_check_rowcompare(key, tuple, tupdesc, dir, continuescan))
                                continue;
                        return false;
                }

                datum = index_getattr(tuple,
                                                          key->sk_attno,
                                                          tupdesc,
                                                          &isNull);

                if (key->sk_flags & SK_ISNULL)
                {
                        /* Handle IS NULL/NOT NULL tests */
                        if (key->sk_flags & SK_SEARCHNULL)
                        {
                                if (isNull)
                                        continue;       /* tuple satisfies this qual */
                        }
                        else
                        {
                                Assert(key->sk_flags & SK_SEARCHNOTNULL);
                                if (!isNull)
                                        continue;       /* tuple satisfies this qual */
                        }

                        /*
                         * Tuple fails this qual.  If it's a required qual for the current
                         * scan direction, then we can conclude no further tuples will
                         * pass, either.
                         */
                        if ((key->sk_flags & SK_BT_REQFWD) &&
                                ScanDirectionIsForward(dir))
                                *continuescan = false;
                        else if ((key->sk_flags & SK_BT_REQBKWD) &&
                                         ScanDirectionIsBackward(dir))
                                *continuescan = false;

                        /*
                         * In any case, this indextuple doesn't match the qual.
                         */
                        return false;
                }

                if (isNull)
                {
                        if (key->sk_flags & SK_BT_NULLS_FIRST)
                        {
                                /*
                                 * Since NULLs are sorted before non-NULLs, we know we have
                                 * reached the lower limit of the range of values for this
                                 * index attr.  On a backward scan, we can stop if this qual
                                 * is one of the "must match" subset.  On a forward scan,
                                 * however, we should keep going.
                                 */
                                if ((key->sk_flags & SK_BT_REQBKWD) &&
                                        ScanDirectionIsBackward(dir))
                                        *continuescan = false;
                        }
                        else
                        {
                                /*
                                 * Since NULLs are sorted after non-NULLs, we know we have
                                 * reached the upper limit of the range of values for this
                                 * index attr.  On a forward scan, we can stop if this qual is
                                 * one of the "must match" subset.      On a backward scan,
                                 * however, we should keep going.
                                 */
                                if ((key->sk_flags & SK_BT_REQFWD) &&
                                        ScanDirectionIsForward(dir))
                                        *continuescan = false;
                        }

                        /*
                         * In any case, this indextuple doesn't match the qual.
                         */
                        return false;
                }

                test = FunctionCall2Coll(&key->sk_func, key->sk_collation,
                                                                 datum, key->sk_argument);

                if (!DatumGetBool(test))
                {
                        /*
                         * Tuple fails this qual.  If it's a required qual for the current
                         * scan direction, then we can conclude no further tuples will
                         * pass, either.
                         *
                         * Note: because we stop the scan as soon as any required equality
                         * qual fails, it is critical that equality quals be used for the
                         * initial positioning in _bt_first() when they are available. See
                         * comments in _bt_first().
                         */
                        if ((key->sk_flags & SK_BT_REQFWD) &&
                                ScanDirectionIsForward(dir))
                                *continuescan = false;
                        else if ((key->sk_flags & SK_BT_REQBKWD) &&
                                         ScanDirectionIsBackward(dir))
                                *continuescan = false;

                        /*
                         * In any case, this indextuple doesn't match the qual.
                         */
                        return false;
                }
        }

        /* If we get here, the tuple passes all index quals. */
        if (tuple_valid)
                scan->xs_ctup.t_self = tuple->t_tid;

        return tuple_valid;
}

/*
 * Test whether an indextuple satisfies a row-comparison scan condition.
 *
 * Return true if so, false if not.  If not, also clear *continuescan if
 * it's not possible for any future tuples in the current scan direction
 * to pass the qual.
 *
 * This is a subroutine for _bt_checkkeys, which see for more info.
 */
static bool
_bt_check_rowcompare(ScanKey skey, IndexTuple tuple, TupleDesc tupdesc,
                                         ScanDirection dir, bool *continuescan)
{
        ScanKey         subkey = (ScanKey) DatumGetPointer(skey->sk_argument);
        int32           cmpresult = 0;
        bool            result;

        /* First subkey should be same as the header says */
        Assert(subkey->sk_attno == skey->sk_attno);

        /* Loop over columns of the row condition */
        for (;;)
        {
                Datum           datum;
                bool            isNull;

                Assert(subkey->sk_flags & SK_ROW_MEMBER);

                datum = index_getattr(tuple,
                                                          subkey->sk_attno,
                                                          tupdesc,
                                                          &isNull);

                if (isNull)
                {
                        if (subkey->sk_flags & SK_BT_NULLS_FIRST)
                        {
                                /*
                                 * Since NULLs are sorted before non-NULLs, we know we have
                                 * reached the lower limit of the range of values for this
                                 * index attr. On a backward scan, we can stop if this qual is
                                 * one of the "must match" subset.      On a forward scan,
                                 * however, we should keep going.
                                 */
                                if ((subkey->sk_flags & SK_BT_REQBKWD) &&
                                        ScanDirectionIsBackward(dir))
                                        *continuescan = false;
                        }
                        else
                        {
                                /*
                                 * Since NULLs are sorted after non-NULLs, we know we have
                                 * reached the upper limit of the range of values for this
                                 * index attr. On a forward scan, we can stop if this qual is
                                 * one of the "must match" subset.      On a backward scan,
                                 * however, we should keep going.
                                 */
                                if ((subkey->sk_flags & SK_BT_REQFWD) &&
                                        ScanDirectionIsForward(dir))
                                        *continuescan = false;
                        }

                        /*
                         * In any case, this indextuple doesn't match the qual.
                         */
                        return false;
                }

                if (subkey->sk_flags & SK_ISNULL)
                {
                        /*
                         * Unlike the simple-scankey case, this isn't a disallowed case.
                         * But it can never match.      If all the earlier row comparison
                         * columns are required for the scan direction, we can stop the
                         * scan, because there can't be another tuple that will succeed.
                         */
                        if (subkey != (ScanKey) DatumGetPointer(skey->sk_argument))
                                subkey--;
                        if ((subkey->sk_flags & SK_BT_REQFWD) &&
                                ScanDirectionIsForward(dir))
                                *continuescan = false;
                        else if ((subkey->sk_flags & SK_BT_REQBKWD) &&
                                         ScanDirectionIsBackward(dir))
                                *continuescan = false;
                        return false;
                }

                /* Perform the test --- three-way comparison not bool operator */
                cmpresult = DatumGetInt32(FunctionCall2Coll(&subkey->sk_func,
                                                                                                        subkey->sk_collation,
                                                                                                        datum,
                                                                                                        subkey->sk_argument));

                if (subkey->sk_flags & SK_BT_DESC)
                        cmpresult = -cmpresult;

                /* Done comparing if unequal, else advance to next column */
                if (cmpresult != 0)
                        break;

                if (subkey->sk_flags & SK_ROW_END)
                        break;
                subkey++;
        }

        /*
         * At this point cmpresult indicates the overall result of the row
         * comparison, and subkey points to the deciding column (or the last
         * column if the result is "=").
         */
        switch (subkey->sk_strategy)
        {
                        /* EQ and NE cases aren't allowed here */
                case BTLessStrategyNumber:
                        result = (cmpresult < 0);
                        break;
                case BTLessEqualStrategyNumber:
                        result = (cmpresult <= 0);
                        break;
                case BTGreaterEqualStrategyNumber:
                        result = (cmpresult >= 0);
                        break;
                case BTGreaterStrategyNumber:
                        result = (cmpresult > 0);
                        break;
                default:
                        elog(ERROR, "unrecognized RowCompareType: %d",
                                 (int) subkey->sk_strategy);
                        result = 0;                     /* keep compiler quiet */
                        break;
        }

        if (!result)
        {
                /*
                 * Tuple fails this qual.  If it's a required qual for the current
                 * scan direction, then we can conclude no further tuples will pass,
                 * either.      Note we have to look at the deciding column, not
                 * necessarily the first or last column of the row condition.
                 */
                if ((subkey->sk_flags & SK_BT_REQFWD) &&
                        ScanDirectionIsForward(dir))
                        *continuescan = false;
                else if ((subkey->sk_flags & SK_BT_REQBKWD) &&
                                 ScanDirectionIsBackward(dir))
                        *continuescan = false;
        }

        return result;
}

/*
 * _bt_killitems - set LP_DEAD state for items an indexscan caller has
 * told us were killed
 *
 * scan->so contains information about the current page and killed tuples
 * thereon (generally, this should only be called if so->numKilled > 0).
 *
 * The caller must have pin on so->currPos.buf, but may or may not have
 * read-lock, as indicated by haveLock.  Note that we assume read-lock
 * is sufficient for setting LP_DEAD status (which is only a hint).
 *
 * We match items by heap TID before assuming they are the right ones to
 * delete.      We cope with cases where items have moved right due to insertions.
 * If an item has moved off the current page due to a split, we'll fail to
 * find it and do nothing (this is not an error case --- we assume the item
 * will eventually get marked in a future indexscan).  Note that because we
 * hold pin on the target page continuously from initially reading the items
 * until applying this function, VACUUM cannot have deleted any items from
 * the page, and so there is no need to search left from the recorded offset.
 * (This observation also guarantees that the item is still the right one
 * to delete, which might otherwise be questionable since heap TIDs can get
 * recycled.)
 */
void
_bt_killitems(IndexScanDesc scan, bool haveLock)
{
        BTScanOpaque so = (BTScanOpaque) scan->opaque;
        Page            page;
        BTPageOpaque opaque;
        OffsetNumber minoff;
        OffsetNumber maxoff;
        int                     i;
        bool            killedsomething = false;

        Assert(BufferIsValid(so->currPos.buf));

        if (!haveLock)
                LockBuffer(so->currPos.buf, BT_READ);

        page = BufferGetPage(so->currPos.buf);
        opaque = (BTPageOpaque) PageGetSpecialPointer(page);
        minoff = P_FIRSTDATAKEY(opaque);
        maxoff = PageGetMaxOffsetNumber(page);

        for (i = 0; i < so->numKilled; i++)
        {
                int                     itemIndex = so->killedItems[i];
                BTScanPosItem *kitem = &so->currPos.items[itemIndex];
                OffsetNumber offnum = kitem->indexOffset;

                Assert(itemIndex >= so->currPos.firstItem &&
                           itemIndex <= so->currPos.lastItem);
                if (offnum < minoff)
                        continue;                       /* pure paranoia */
                while (offnum <= maxoff)
                {
                        ItemId          iid = PageGetItemId(page, offnum);
                        IndexTuple      ituple = (IndexTuple) PageGetItem(page, iid);

                        if (ItemPointerEquals(&ituple->t_tid, &kitem->heapTid))
                        {
                                /* found the item */
                                ItemIdMarkDead(iid);
                                killedsomething = true;
                                break;                  /* out of inner search loop */
                        }
                        offnum = OffsetNumberNext(offnum);
                }
        }

        /*
         * Since this can be redone later if needed, it's treated the same as a
         * commit-hint-bit status update for heap tuples: we mark the buffer dirty
         * but don't make a WAL log entry.
         *
         * Whenever we mark anything LP_DEAD, we also set the page's
         * BTP_HAS_GARBAGE flag, which is likewise just a hint.
         */
        if (killedsomething)
        {
                opaque->btpo_flags |= BTP_HAS_GARBAGE;
                SetBufferCommitInfoNeedsSave(so->currPos.buf);
        }

        if (!haveLock)
                LockBuffer(so->currPos.buf, BUFFER_LOCK_UNLOCK);

        /*
         * Always reset the scan state, so we don't look for same items on other
         * pages.
         */
        so->numKilled = 0;
}


/*
 * The following routines manage a shared-memory area in which we track
 * assignment of "vacuum cycle IDs" to currently-active btree vacuuming
 * operations.  There is a single counter which increments each time we
 * start a vacuum to assign it a cycle ID.      Since multiple vacuums could
 * be active concurrently, we have to track the cycle ID for each active
 * vacuum; this requires at most MaxBackends entries (usually far fewer).
 * We assume at most one vacuum can be active for a given index.
 *
 * Access to the shared memory area is controlled by BtreeVacuumLock.
 * In principle we could use a separate lmgr locktag for each index,
 * but a single LWLock is much cheaper, and given the short time that
 * the lock is ever held, the concurrency hit should be minimal.
 */

typedef struct BTOneVacInfo
{
        LockRelId       relid;                  /* global identifier of an index */
        BTCycleId       cycleid;                /* cycle ID for its active VACUUM */
} BTOneVacInfo;

typedef struct BTVacInfo
{
        BTCycleId       cycle_ctr;              /* cycle ID most recently assigned */
        int                     num_vacuums;    /* number of currently active VACUUMs */
        int                     max_vacuums;    /* allocated length of vacuums[] array */
        BTOneVacInfo vacuums[1];        /* VARIABLE LENGTH ARRAY */
} BTVacInfo;

static BTVacInfo *btvacinfo;


/*
 * _bt_vacuum_cycleid --- get the active vacuum cycle ID for an index,
 *              or zero if there is no active VACUUM
 *
 * Note: for correct interlocking, the caller must already hold pin and
 * exclusive lock on each buffer it will store the cycle ID into.  This
 * ensures that even if a VACUUM starts immediately afterwards, it cannot
 * process those pages until the page split is complete.
 */
BTCycleId
_bt_vacuum_cycleid(Relation rel)
{
        BTCycleId       result = 0;
        int                     i;

        /* Share lock is enough since this is a read-only operation */
        LWLockAcquire(BtreeVacuumLock, LW_SHARED);

        for (i = 0; i < btvacinfo->num_vacuums; i++)
        {
                BTOneVacInfo *vac = &btvacinfo->vacuums[i];

                if (vac->relid.relId == rel->rd_lockInfo.lockRelId.relId &&
                        vac->relid.dbId == rel->rd_lockInfo.lockRelId.dbId)
                {
                        result = vac->cycleid;
                        break;
                }
        }

        LWLockRelease(BtreeVacuumLock);
        return result;
}

/*
 * _bt_start_vacuum --- assign a cycle ID to a just-starting VACUUM operation
 *
 * Note: the caller must guarantee that it will eventually call
 * _bt_end_vacuum, else we'll permanently leak an array slot.  To ensure
 * that this happens even in elog(FATAL) scenarios, the appropriate coding
 * is not just a PG_TRY, but
 *              PG_ENSURE_ERROR_CLEANUP(_bt_end_vacuum_callback, PointerGetDatum(rel))
 */
BTCycleId
_bt_start_vacuum(Relation rel)
{
        BTCycleId       result;
        int                     i;
        BTOneVacInfo *vac;

        LWLockAcquire(BtreeVacuumLock, LW_EXCLUSIVE);

        /*
         * Assign the next cycle ID, being careful to avoid zero as well as the
         * reserved high values.
         */
        result = ++(btvacinfo->cycle_ctr);
        if (result == 0 || result > MAX_BT_CYCLE_ID)
                result = btvacinfo->cycle_ctr = 1;

        /* Let's just make sure there's no entry already for this index */
        for (i = 0; i < btvacinfo->num_vacuums; i++)
        {
                vac = &btvacinfo->vacuums[i];
                if (vac->relid.relId == rel->rd_lockInfo.lockRelId.relId &&
                        vac->relid.dbId == rel->rd_lockInfo.lockRelId.dbId)
                {
                        /*
                         * Unlike most places in the backend, we have to explicitly
                         * release our LWLock before throwing an error.  This is because
                         * we expect _bt_end_vacuum() to be called before transaction
                         * abort cleanup can run to release LWLocks.
                         */
                        LWLockRelease(BtreeVacuumLock);
                        elog(ERROR, "multiple active vacuums for index \"%s\"",
                                 RelationGetRelationName(rel));
                }
        }

        /* OK, add an entry */
        if (btvacinfo->num_vacuums >= btvacinfo->max_vacuums)
        {
                LWLockRelease(BtreeVacuumLock);
                elog(ERROR, "out of btvacinfo slots");
        }
        vac = &btvacinfo->vacuums[btvacinfo->num_vacuums];
        vac->relid = rel->rd_lockInfo.lockRelId;
        vac->cycleid = result;
        btvacinfo->num_vacuums++;

        LWLockRelease(BtreeVacuumLock);
        return result;
}

/*
 * _bt_end_vacuum --- mark a btree VACUUM operation as done
 *
 * Note: this is deliberately coded not to complain if no entry is found;
 * this allows the caller to put PG_TRY around the start_vacuum operation.
 */
void
_bt_end_vacuum(Relation rel)
{
        int                     i;

        LWLockAcquire(BtreeVacuumLock, LW_EXCLUSIVE);

        /* Find the array entry */
        for (i = 0; i < btvacinfo->num_vacuums; i++)
        {
                BTOneVacInfo *vac = &btvacinfo->vacuums[i];

                if (vac->relid.relId == rel->rd_lockInfo.lockRelId.relId &&
                        vac->relid.dbId == rel->rd_lockInfo.lockRelId.dbId)
                {
                        /* Remove it by shifting down the last entry */
                        *vac = btvacinfo->vacuums[btvacinfo->num_vacuums - 1];
                        btvacinfo->num_vacuums--;
                        break;
                }
        }

        LWLockRelease(BtreeVacuumLock);
}

/*
 * _bt_end_vacuum wrapped as an on_shmem_exit callback function
 */
void
_bt_end_vacuum_callback(int code, Datum arg)
{
        _bt_end_vacuum((Relation) DatumGetPointer(arg));
}

/*
 * BTreeShmemSize --- report amount of shared memory space needed
 */
Size
BTreeShmemSize(void)
{
        Size            size;

        size = offsetof(BTVacInfo, vacuums[0]);
        size = add_size(size, mul_size(MaxBackends, sizeof(BTOneVacInfo)));
        return size;
}

/*
 * BTreeShmemInit --- initialize this module's shared memory
 */
void
BTreeShmemInit(void)
{
        bool            found;

        btvacinfo = (BTVacInfo *) ShmemInitStruct("BTree Vacuum State",
                                                                                          BTreeShmemSize(),
                                                                                          &found);

        if (!IsUnderPostmaster)
        {
                /* Initialize shared memory area */
                Assert(!found);

                /*
                 * It doesn't really matter what the cycle counter starts at, but
                 * having it always start the same doesn't seem good.  Seed with
                 * low-order bits of time() instead.
                 */
                btvacinfo->cycle_ctr = (BTCycleId) time(NULL);

                btvacinfo->num_vacuums = 0;
                btvacinfo->max_vacuums = MaxBackends;
        }
        else
                Assert(found);
}

Datum
btoptions(PG_FUNCTION_ARGS)
{
        Datum           reloptions = PG_GETARG_DATUM(0);
        bool            validate = PG_GETARG_BOOL(1);
        bytea      *result;

        result = default_reloptions(reloptions, validate, RELOPT_KIND_BTREE);
        if (result)
                PG_RETURN_BYTEA_P(result);
        PG_RETURN_NULL();
}