brin_inclusion.c

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/*
 * brin_inclusion.c
 *      Implementation of inclusion opclasses for BRIN
 *
 * This module provides framework BRIN support functions for the "inclusion"
 * operator classes.  A few SQL-level support functions are also required for
 * each opclass.
 *
 * The "inclusion" BRIN strategy is useful for types that support R-Tree
 * operations.  This implementation is a straight mapping of those operations
 * to the block-range nature of BRIN, with two exceptions: (a) we explicitly
 * support "empty" elements: at least with range types, we need to consider
 * emptiness separately from regular R-Tree strategies; and (b) we need to
 * consider "unmergeable" elements, that is, a set of elements for whose union
 * no representation exists.  The only case where that happens as of this
 * writing is the INET type, where IPv6 values cannot be merged with IPv4
 * values.
 *
 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/access/brin/brin_inclusion.c
 */
#include "postgres.h"

#include "access/brin_internal.h"
#include "access/brin_tuple.h"
#include "access/genam.h"
#include "access/skey.h"
#include "catalog/pg_amop.h"
#include "catalog/pg_type.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/syscache.h"


/*
 * Additional SQL level support functions
 *
 * Procedure numbers must not use values reserved for BRIN itself; see
 * brin_internal.h.
 */
#define     INCLUSION_MAX_PROCNUMS  4   /* maximum support procs we need */
#define     PROCNUM_MERGE           11  /* required */
#define     PROCNUM_MERGEABLE       12  /* optional */
#define     PROCNUM_CONTAINS        13  /* optional */
#define     PROCNUM_EMPTY           14  /* optional */


/*
 * Subtract this from procnum to obtain index in InclusionOpaque arrays
 * (Must be equal to minimum of private procnums).
 */
#define     PROCNUM_BASE            11

/*-
 * The values stored in the bv_values arrays correspond to:
 *
 * INCLUSION_UNION
 *      the union of the values in the block range
 * INCLUSION_UNMERGEABLE
 *      whether the values in the block range cannot be merged
 *      (e.g. an IPv6 address amidst IPv4 addresses)
 * INCLUSION_CONTAINS_EMPTY
 *      whether an empty value is present in any tuple
 *      in the block range
 */
#define INCLUSION_UNION             0
#define INCLUSION_UNMERGEABLE       1
#define INCLUSION_CONTAINS_EMPTY    2


typedef struct InclusionOpaque
{
    FmgrInfo    extra_procinfos[INCLUSION_MAX_PROCNUMS];
    bool        extra_proc_missing[INCLUSION_MAX_PROCNUMS];
    Oid         cached_subtype;
    FmgrInfo    strategy_procinfos[RTMaxStrategyNumber];
} InclusionOpaque;

static FmgrInfo *inclusion_get_procinfo(BrinDesc *bdesc, uint16 attno,
                                        uint16 procnum);
static FmgrInfo *inclusion_get_strategy_procinfo(BrinDesc *bdesc, uint16 attno,
                                                 Oid subtype, uint16 strategynum);


/*
 * BRIN inclusion OpcInfo function
 */
Datum
brin_inclusion_opcinfo(PG_FUNCTION_ARGS)
{
    Oid         typoid = PG_GETARG_OID(0);
    BrinOpcInfo *result;
    TypeCacheEntry *bool_typcache = lookup_type_cache(BOOLOID, 0);

    /*
     * All members of opaque are initialized lazily; both procinfo arrays
     * start out as non-initialized by having fn_oid be InvalidOid, and
     * "missing" to false, by zeroing here.  strategy_procinfos elements can
     * be invalidated when cached_subtype changes by zeroing fn_oid.
     * extra_procinfo entries are never invalidated, but if a lookup fails
     * (which is expected), extra_proc_missing is set to true, indicating not
     * to look it up again.
     */
    result = palloc0(MAXALIGN(SizeofBrinOpcInfo(3)) + sizeof(InclusionOpaque));
    result->oi_nstored = 3;
    result->oi_opaque = (InclusionOpaque *)
        MAXALIGN((char *) result + SizeofBrinOpcInfo(3));

    /* the union */
    result->oi_typcache[INCLUSION_UNION] =
        lookup_type_cache(typoid, 0);

    /* includes elements that are not mergeable */
    result->oi_typcache[INCLUSION_UNMERGEABLE] = bool_typcache;

    /* includes the empty element */
    result->oi_typcache[INCLUSION_CONTAINS_EMPTY] = bool_typcache;

    PG_RETURN_POINTER(result);
}

/*
 * BRIN inclusion add value function
 *
 * Examine the given index tuple (which contains partial status of a certain
 * page range) by comparing it to the given value that comes from another heap
 * tuple.  If the new value is outside the union specified by the existing
 * tuple values, update the index tuple and return true.  Otherwise, return
 * false and do not modify in this case.
 */
Datum
brin_inclusion_add_value(PG_FUNCTION_ARGS)
{
    BrinDesc   *bdesc = (BrinDesc *) PG_GETARG_POINTER(0);
    BrinValues *column = (BrinValues *) PG_GETARG_POINTER(1);
    Datum       newval = PG_GETARG_DATUM(2);
    bool        isnull = PG_GETARG_BOOL(3);
    Oid         colloid = PG_GET_COLLATION();
    FmgrInfo   *finfo;
    Datum       result;
    bool        new = false;
    AttrNumber  attno;
    Form_pg_attribute attr;

    /*
     * If the new value is null, we record that we saw it if it's the first
     * one; otherwise, there's nothing to do.
     */
    if (isnull)
    {
        if (column->bv_hasnulls)
            PG_RETURN_BOOL(false);

        column->bv_hasnulls = true;
        PG_RETURN_BOOL(true);
    }

    attno = column->bv_attno;
    attr = TupleDescAttr(bdesc->bd_tupdesc, attno - 1);

    /*
     * If the recorded value is null, copy the new value (which we know to be
     * not null), and we're almost done.
     */
    if (column->bv_allnulls)
    {
        column->bv_values[INCLUSION_UNION] =
            datumCopy(newval, attr->attbyval, attr->attlen);
        column->bv_values[INCLUSION_UNMERGEABLE] = BoolGetDatum(false);
        column->bv_values[INCLUSION_CONTAINS_EMPTY] = BoolGetDatum(false);
        column->bv_allnulls = false;
        new = true;
    }

    /*
     * No need for further processing if the block range is marked as
     * containing unmergeable values.
     */
    if (DatumGetBool(column->bv_values[INCLUSION_UNMERGEABLE]))
        PG_RETURN_BOOL(false);

    /*
     * If the opclass supports the concept of empty values, test the passed
     * new value for emptiness; if it returns true, we need to set the
     * "contains empty" flag in the element (unless already set).
     */
    finfo = inclusion_get_procinfo(bdesc, attno, PROCNUM_EMPTY);
    if (finfo != NULL && DatumGetBool(FunctionCall1Coll(finfo, colloid, newval)))
    {
        if (!DatumGetBool(column->bv_values[INCLUSION_CONTAINS_EMPTY]))
        {
            column->bv_values[INCLUSION_CONTAINS_EMPTY] = BoolGetDatum(true);
            PG_RETURN_BOOL(true);
        }

        PG_RETURN_BOOL(false);
    }

    if (new)
        PG_RETURN_BOOL(true);

    /* Check if the new value is already contained. */
    finfo = inclusion_get_procinfo(bdesc, attno, PROCNUM_CONTAINS);
    if (finfo != NULL &&
        DatumGetBool(FunctionCall2Coll(finfo, colloid,
                                       column->bv_values[INCLUSION_UNION],
                                       newval)))
        PG_RETURN_BOOL(false);

    /*
     * Check if the new value is mergeable to the existing union.  If it is
     * not, mark the value as containing unmergeable elements and get out.
     *
     * Note: at this point we could remove the value from the union, since
     * it's not going to be used any longer.  However, the BRIN framework
     * doesn't allow for the value not being present.  Improve someday.
     */
    finfo = inclusion_get_procinfo(bdesc, attno, PROCNUM_MERGEABLE);
    if (finfo != NULL &&
        !DatumGetBool(FunctionCall2Coll(finfo, colloid,
                                        column->bv_values[INCLUSION_UNION],
                                        newval)))
    {
        column->bv_values[INCLUSION_UNMERGEABLE] = BoolGetDatum(true);
        PG_RETURN_BOOL(true);
    }

    /* Finally, merge the new value to the existing union. */
    finfo = inclusion_get_procinfo(bdesc, attno, PROCNUM_MERGE);
    Assert(finfo != NULL);
    result = FunctionCall2Coll(finfo, colloid,
                               column->bv_values[INCLUSION_UNION], newval);
    if (!attr->attbyval)
        pfree(DatumGetPointer(column->bv_values[INCLUSION_UNION]));
    column->bv_values[INCLUSION_UNION] = result;

    PG_RETURN_BOOL(true);
}

/*
 * BRIN inclusion consistent function
 *
 * All of the strategies are optional.
 */
Datum
brin_inclusion_consistent(PG_FUNCTION_ARGS)
{
    BrinDesc   *bdesc = (BrinDesc *) PG_GETARG_POINTER(0);
    BrinValues *column = (BrinValues *) PG_GETARG_POINTER(1);
    ScanKey     key = (ScanKey) PG_GETARG_POINTER(2);
    Oid         colloid = PG_GET_COLLATION(),
                subtype;
    Datum       unionval;
    AttrNumber  attno;
    Datum       query;
    FmgrInfo   *finfo;
    Datum       result;

    Assert(key->sk_attno == column->bv_attno);

    /* Handle IS NULL/IS NOT NULL tests. */
    if (key->sk_flags & SK_ISNULL)
    {
        if (key->sk_flags & SK_SEARCHNULL)
        {
            if (column->bv_allnulls || column->bv_hasnulls)
                PG_RETURN_BOOL(true);
            PG_RETURN_BOOL(false);
        }

        /*
         * For IS NOT NULL, we can only skip ranges that are known to have
         * only nulls.
         */
        if (key->sk_flags & SK_SEARCHNOTNULL)
            PG_RETURN_BOOL(!column->bv_allnulls);

        /*
         * Neither IS NULL nor IS NOT NULL was used; assume all indexable
         * operators are strict and return false.
         */
        PG_RETURN_BOOL(false);
    }

    /* If it is all nulls, it cannot possibly be consistent. */
    if (column->bv_allnulls)
        PG_RETURN_BOOL(false);

    /* It has to be checked, if it contains elements that are not mergeable. */
    if (DatumGetBool(column->bv_values[INCLUSION_UNMERGEABLE]))
        PG_RETURN_BOOL(true);

    attno = key->sk_attno;
    subtype = key->sk_subtype;
    query = key->sk_argument;
    unionval = column->bv_values[INCLUSION_UNION];
    switch (key->sk_strategy)
    {
            /*
             * Placement strategies
             *
             * These are implemented by logically negating the result of the
             * converse placement operator; for this to work, the converse
             * operator must be part of the opclass.  An error will be thrown
             * by inclusion_get_strategy_procinfo() if the required strategy
             * is not part of the opclass.
             *
             * These all return false if either argument is empty, so there is
             * no need to check for empty elements.
             */

        case RTLeftStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTOverRightStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            PG_RETURN_BOOL(!DatumGetBool(result));

        case RTOverLeftStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTRightStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            PG_RETURN_BOOL(!DatumGetBool(result));

        case RTOverRightStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTLeftStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            PG_RETURN_BOOL(!DatumGetBool(result));

        case RTRightStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTOverLeftStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            PG_RETURN_BOOL(!DatumGetBool(result));

        case RTBelowStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTOverAboveStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            PG_RETURN_BOOL(!DatumGetBool(result));

        case RTOverBelowStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTAboveStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            PG_RETURN_BOOL(!DatumGetBool(result));

        case RTOverAboveStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTBelowStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            PG_RETURN_BOOL(!DatumGetBool(result));

        case RTAboveStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTOverBelowStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            PG_RETURN_BOOL(!DatumGetBool(result));

            /*
             * Overlap and contains strategies
             *
             * These strategies are simple enough that we can simply call the
             * operator and return its result.  Empty elements don't change
             * the result.
             */

        case RTOverlapStrategyNumber:
        case RTContainsStrategyNumber:
        case RTOldContainsStrategyNumber:
        case RTContainsElemStrategyNumber:
        case RTSubStrategyNumber:
        case RTSubEqualStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    key->sk_strategy);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            PG_RETURN_DATUM(result);

            /*
             * Contained by strategies
             *
             * We cannot just call the original operator for the contained by
             * strategies because some elements can be contained even though
             * the union is not; instead we use the overlap operator.
             *
             * We check for empty elements separately as they are not merged
             * to the union but contained by everything.
             */

        case RTContainedByStrategyNumber:
        case RTOldContainedByStrategyNumber:
        case RTSuperStrategyNumber:
        case RTSuperEqualStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTOverlapStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            if (DatumGetBool(result))
                PG_RETURN_BOOL(true);

            PG_RETURN_DATUM(column->bv_values[INCLUSION_CONTAINS_EMPTY]);

            /*
             * Adjacent strategy
             *
             * We test for overlap first but to be safe we need to call the
             * actual adjacent operator also.
             *
             * An empty element cannot be adjacent to any other, so there is
             * no need to check for it.
             */

        case RTAdjacentStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTOverlapStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            if (DatumGetBool(result))
                PG_RETURN_BOOL(true);

            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTAdjacentStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            PG_RETURN_DATUM(result);

            /*
             * Basic comparison strategies
             *
             * It is straightforward to support the equality strategies with
             * the contains operator.  Generally, inequality strategies do not
             * make much sense for the types which will be used with the
             * inclusion BRIN family of opclasses, but it is possible to
             * implement them with logical negation of the left-of and
             * right-of operators.
             *
             * NB: These strategies cannot be used with geometric datatypes
             * that use comparison of areas!  The only exception is the "same"
             * strategy.
             *
             * Empty elements are considered to be less than the others.  We
             * cannot use the empty support function to check the query is an
             * empty element, because the query can be another data type than
             * the empty support function argument.  So we will return true,
             * if there is a possibility that empty elements will change the
             * result.
             */

        case RTLessStrategyNumber:
        case RTLessEqualStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTRightStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            if (!DatumGetBool(result))
                PG_RETURN_BOOL(true);

            PG_RETURN_DATUM(column->bv_values[INCLUSION_CONTAINS_EMPTY]);

        case RTSameStrategyNumber:
        case RTEqualStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTContainsStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            if (DatumGetBool(result))
                PG_RETURN_BOOL(true);

            PG_RETURN_DATUM(column->bv_values[INCLUSION_CONTAINS_EMPTY]);

        case RTGreaterEqualStrategyNumber:
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTLeftStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            if (!DatumGetBool(result))
                PG_RETURN_BOOL(true);

            PG_RETURN_DATUM(column->bv_values[INCLUSION_CONTAINS_EMPTY]);

        case RTGreaterStrategyNumber:
            /* no need to check for empty elements */
            finfo = inclusion_get_strategy_procinfo(bdesc, attno, subtype,
                                                    RTLeftStrategyNumber);
            result = FunctionCall2Coll(finfo, colloid, unionval, query);
            PG_RETURN_BOOL(!DatumGetBool(result));

        default:
            /* shouldn't happen */
            elog(ERROR, "invalid strategy number %d", key->sk_strategy);
            PG_RETURN_BOOL(false);
    }
}

/*
 * BRIN inclusion union function
 *
 * Given two BrinValues, update the first of them as a union of the summary
 * values contained in both.  The second one is untouched.
 */
Datum
brin_inclusion_union(PG_FUNCTION_ARGS)
{
    BrinDesc   *bdesc = (BrinDesc *) PG_GETARG_POINTER(0);
    BrinValues *col_a = (BrinValues *) PG_GETARG_POINTER(1);
    BrinValues *col_b = (BrinValues *) PG_GETARG_POINTER(2);
    Oid         colloid = PG_GET_COLLATION();
    AttrNumber  attno;
    Form_pg_attribute attr;
    FmgrInfo   *finfo;
    Datum       result;

    Assert(col_a->bv_attno == col_b->bv_attno);

    /* Adjust "hasnulls". */
    if (!col_a->bv_hasnulls && col_b->bv_hasnulls)
        col_a->bv_hasnulls = true;

    /* If there are no values in B, there's nothing left to do. */
    if (col_b->bv_allnulls)
        PG_RETURN_VOID();

    attno = col_a->bv_attno;
    attr = TupleDescAttr(bdesc->bd_tupdesc, attno - 1);

    /*
     * Adjust "allnulls".  If A doesn't have values, just copy the values from
     * B into A, and we're done.  We cannot run the operators in this case,
     * because values in A might contain garbage.  Note we already established
     * that B contains values.
     */
    if (col_a->bv_allnulls)
    {
        col_a->bv_allnulls = false;
        col_a->bv_values[INCLUSION_UNION] =
            datumCopy(col_b->bv_values[INCLUSION_UNION],
                      attr->attbyval, attr->attlen);
        col_a->bv_values[INCLUSION_UNMERGEABLE] =
            col_b->bv_values[INCLUSION_UNMERGEABLE];
        col_a->bv_values[INCLUSION_CONTAINS_EMPTY] =
            col_b->bv_values[INCLUSION_CONTAINS_EMPTY];
        PG_RETURN_VOID();
    }

    /* If B includes empty elements, mark A similarly, if needed. */
    if (!DatumGetBool(col_a->bv_values[INCLUSION_CONTAINS_EMPTY]) &&
        DatumGetBool(col_b->bv_values[INCLUSION_CONTAINS_EMPTY]))
        col_a->bv_values[INCLUSION_CONTAINS_EMPTY] = BoolGetDatum(true);

    /* Check if A includes elements that are not mergeable. */
    if (DatumGetBool(col_a->bv_values[INCLUSION_UNMERGEABLE]))
        PG_RETURN_VOID();

    /* If B includes elements that are not mergeable, mark A similarly. */
    if (DatumGetBool(col_b->bv_values[INCLUSION_UNMERGEABLE]))
    {
        col_a->bv_values[INCLUSION_UNMERGEABLE] = BoolGetDatum(true);
        PG_RETURN_VOID();
    }

    /* Check if A and B are mergeable; if not, mark A unmergeable. */
    finfo = inclusion_get_procinfo(bdesc, attno, PROCNUM_MERGEABLE);
    if (finfo != NULL &&
        !DatumGetBool(FunctionCall2Coll(finfo, colloid,
                                        col_a->bv_values[INCLUSION_UNION],
                                        col_b->bv_values[INCLUSION_UNION])))
    {
        col_a->bv_values[INCLUSION_UNMERGEABLE] = BoolGetDatum(true);
        PG_RETURN_VOID();
    }

    /* Finally, merge B to A. */
    finfo = inclusion_get_procinfo(bdesc, attno, PROCNUM_MERGE);
    Assert(finfo != NULL);
    result = FunctionCall2Coll(finfo, colloid,
                               col_a->bv_values[INCLUSION_UNION],
                               col_b->bv_values[INCLUSION_UNION]);
    if (!attr->attbyval)
        pfree(DatumGetPointer(col_a->bv_values[INCLUSION_UNION]));
    col_a->bv_values[INCLUSION_UNION] = result;

    PG_RETURN_VOID();
}

/*
 * Cache and return inclusion opclass support procedure
 *
 * Return the procedure corresponding to the given function support number
 * or null if it is not exists.
 */
static FmgrInfo *
inclusion_get_procinfo(BrinDesc *bdesc, uint16 attno, uint16 procnum)
{
    InclusionOpaque *opaque;
    uint16      basenum = procnum - PROCNUM_BASE;

    /*
     * We cache these in the opaque struct, to avoid repetitive syscache
     * lookups.
     */
    opaque = (InclusionOpaque *) bdesc->bd_info[attno - 1]->oi_opaque;

    /*
     * If we already searched for this proc and didn't find it, don't bother
     * searching again.
     */
    if (opaque->extra_proc_missing[basenum])
        return NULL;

    if (opaque->extra_procinfos[basenum].fn_oid == InvalidOid)
    {
        if (RegProcedureIsValid(index_getprocid(bdesc->bd_index, attno,
                                                procnum)))
        {
            fmgr_info_copy(&opaque->extra_procinfos[basenum],
                           index_getprocinfo(bdesc->bd_index, attno, procnum),
                           bdesc->bd_context);
        }
        else
        {
            opaque->extra_proc_missing[basenum] = true;
            return NULL;
        }
    }

    return &opaque->extra_procinfos[basenum];
}

/*
 * Cache and return the procedure of the given strategy
 *
 * Return the procedure corresponding to the given sub-type and strategy
 * number.  The data type of the index will be used as the left hand side of
 * the operator and the given sub-type will be used as the right hand side.
 * Throws an error if the pg_amop row does not exist, but that should not
 * happen with a properly configured opclass.
 *
 * It always throws an error when the data type of the opclass is different
 * from the data type of the column or the expression.  That happens when the
 * column data type has implicit cast to the opclass data type.  We don't
 * bother casting types, because this situation can easily be avoided by
 * setting storage data type to that of the opclass.  The same problem does not
 * apply to the data type of the right hand side, because the type in the
 * ScanKey always matches the opclass' one.
 *
 * Note: this function mirrors minmax_get_strategy_procinfo; if changes are
 * made here, see that function too.
 */
static FmgrInfo *
inclusion_get_strategy_procinfo(BrinDesc *bdesc, uint16 attno, Oid subtype,
                                uint16 strategynum)
{
    InclusionOpaque *opaque;

    Assert(strategynum >= 1 &&
           strategynum <= RTMaxStrategyNumber);

    opaque = (InclusionOpaque *) bdesc->bd_info[attno - 1]->oi_opaque;

    /*
     * We cache the procedures for the last sub-type in the opaque struct, to
     * avoid repetitive syscache lookups.  If the sub-type is changed,
     * invalidate all the cached entries.
     */
    if (opaque->cached_subtype != subtype)
    {
        uint16      i;

        for (i = 1; i <= RTMaxStrategyNumber; i++)
            opaque->strategy_procinfos[i - 1].fn_oid = InvalidOid;
        opaque->cached_subtype = subtype;
    }

    if (opaque->strategy_procinfos[strategynum - 1].fn_oid == InvalidOid)
    {
        Form_pg_attribute attr;
        HeapTuple   tuple;
        Oid         opfamily,
                    oprid;
        bool        isNull;

        opfamily = bdesc->bd_index->rd_opfamily[attno - 1];
        attr = TupleDescAttr(bdesc->bd_tupdesc, attno - 1);
        tuple = SearchSysCache4(AMOPSTRATEGY, ObjectIdGetDatum(opfamily),
                                ObjectIdGetDatum(attr->atttypid),
                                ObjectIdGetDatum(subtype),
                                Int16GetDatum(strategynum));

        if (!HeapTupleIsValid(tuple))
            elog(ERROR, "missing operator %d(%u,%u) in opfamily %u",
                 strategynum, attr->atttypid, subtype, opfamily);

        oprid = DatumGetObjectId(SysCacheGetAttr(AMOPSTRATEGY, tuple,
                                                 Anum_pg_amop_amopopr, &isNull));
        ReleaseSysCache(tuple);
        Assert(!isNull && RegProcedureIsValid(oprid));

        fmgr_info_cxt(get_opcode(oprid),
                      &opaque->strategy_procinfos[strategynum - 1],
                      bdesc->bd_context);
    }

    return &opaque->strategy_procinfos[strategynum - 1];
}