attribute_stats.c

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/*-------------------------------------------------------------------------
 * attribute_stats.c
 *
 *    PostgreSQL relation attribute statistics manipulation.
 *
 * Code supporting the direct import of relation attribute statistics, similar
 * to what is done by the ANALYZE command.
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *       src/backend/statistics/attribute_stats.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/heapam.h"
#include "catalog/indexing.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_operator.h"
#include "nodes/nodeFuncs.h"
#include "statistics/statistics.h"
#include "statistics/stat_utils.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"
 
#define DEFAULT_NULL_FRAC      Float4GetDatum(0.0)
#define DEFAULT_AVG_WIDTH      Int32GetDatum(0) /* unknown */
#define DEFAULT_N_DISTINCT     Float4GetDatum(0.0)  /* unknown */
 
enum attribute_stats_argnum
{
    ATTRELATION_ARG = 0,
    ATTNAME_ARG,
    INHERITED_ARG,
    NULL_FRAC_ARG,
    AVG_WIDTH_ARG,
    N_DISTINCT_ARG,
    MOST_COMMON_VALS_ARG,
    MOST_COMMON_FREQS_ARG,
    HISTOGRAM_BOUNDS_ARG,
    CORRELATION_ARG,
    MOST_COMMON_ELEMS_ARG,
    MOST_COMMON_ELEM_FREQS_ARG,
    ELEM_COUNT_HISTOGRAM_ARG,
    RANGE_LENGTH_HISTOGRAM_ARG,
    RANGE_EMPTY_FRAC_ARG,
    RANGE_BOUNDS_HISTOGRAM_ARG,
    NUM_ATTRIBUTE_STATS_ARGS
};
 
static struct StatsArgInfo attarginfo[] =
{
    [ATTRELATION_ARG] = {"relation", REGCLASSOID},
    [ATTNAME_ARG] = {"attname", NAMEOID},
    [INHERITED_ARG] = {"inherited", BOOLOID},
    [NULL_FRAC_ARG] = {"null_frac", FLOAT4OID},
    [AVG_WIDTH_ARG] = {"avg_width", INT4OID},
    [N_DISTINCT_ARG] = {"n_distinct", FLOAT4OID},
    [MOST_COMMON_VALS_ARG] = {"most_common_vals", TEXTOID},
    [MOST_COMMON_FREQS_ARG] = {"most_common_freqs", FLOAT4ARRAYOID},
    [HISTOGRAM_BOUNDS_ARG] = {"histogram_bounds", TEXTOID},
    [CORRELATION_ARG] = {"correlation", FLOAT4OID},
    [MOST_COMMON_ELEMS_ARG] = {"most_common_elems", TEXTOID},
    [MOST_COMMON_ELEM_FREQS_ARG] = {"most_common_elem_freqs", FLOAT4ARRAYOID},
    [ELEM_COUNT_HISTOGRAM_ARG] = {"elem_count_histogram", FLOAT4ARRAYOID},
    [RANGE_LENGTH_HISTOGRAM_ARG] = {"range_length_histogram", TEXTOID},
    [RANGE_EMPTY_FRAC_ARG] = {"range_empty_frac", FLOAT4OID},
    [RANGE_BOUNDS_HISTOGRAM_ARG] = {"range_bounds_histogram", TEXTOID},
    [NUM_ATTRIBUTE_STATS_ARGS] = {0}
};
 
static bool attribute_statistics_update(FunctionCallInfo fcinfo, int elevel);
static Node *get_attr_expr(Relation rel, int attnum);
static void get_attr_stat_type(Oid reloid, AttrNumber attnum, int elevel,
                               Oid *atttypid, int32 *atttypmod,
                               char *atttyptype, Oid *atttypcoll,
                               Oid *eq_opr, Oid *lt_opr);
static bool get_elem_stat_type(Oid atttypid, char atttyptype, int elevel,
                               Oid *elemtypid, Oid *elem_eq_opr);
static Datum text_to_stavalues(const char *staname, FmgrInfo *array_in, Datum d,
                               Oid typid, int32 typmod, int elevel, bool *ok);
static void set_stats_slot(Datum *values, bool *nulls, bool *replaces,
                           int16 stakind, Oid staop, Oid stacoll,
                           Datum stanumbers, bool stanumbers_isnull,
                           Datum stavalues, bool stavalues_isnull);
static void upsert_pg_statistic(Relation starel, HeapTuple oldtup,
                                Datum *values, bool *nulls, bool *replaces);
static bool delete_pg_statistic(Oid reloid, AttrNumber attnum, bool stainherit);
static void init_empty_stats_tuple(Oid reloid, int16 attnum, bool inherited,
                                   Datum *values, bool *nulls, bool *replaces);
 
/*
 * Insert or Update Attribute Statistics
 *
 * See pg_statistic.h for an explanation of how each statistic kind is
 * stored. Custom statistics kinds are not supported.
 *
 * Depending on the statistics kind, we need to derive information from the
 * attribute for which we're storing the stats. For instance, the MCVs are
 * stored as an anyarray, and the representation of the array needs to store
 * the correct element type, which must be derived from the attribute.
 *
 * Major errors, such as the table not existing, the attribute not existing,
 * or a permissions failure are always reported at ERROR. Other errors, such
 * as a conversion failure on one statistic kind, are reported at 'elevel',
 * and other statistic kinds may still be updated.
 */
static bool
attribute_statistics_update(FunctionCallInfo fcinfo, int elevel)
{
    Oid         reloid;
    Name        attname;
    bool        inherited;
    AttrNumber  attnum;
 
    Relation    starel;
    HeapTuple   statup;
 
    Oid         atttypid = InvalidOid;
    int32       atttypmod;
    char        atttyptype;
    Oid         atttypcoll = InvalidOid;
    Oid         eq_opr = InvalidOid;
    Oid         lt_opr = InvalidOid;
 
    Oid         elemtypid = InvalidOid;
    Oid         elem_eq_opr = InvalidOid;
 
    FmgrInfo    array_in_fn;
 
    bool        do_mcv = !PG_ARGISNULL(MOST_COMMON_FREQS_ARG) &&
        !PG_ARGISNULL(MOST_COMMON_VALS_ARG);
    bool        do_histogram = !PG_ARGISNULL(HISTOGRAM_BOUNDS_ARG);
    bool        do_correlation = !PG_ARGISNULL(CORRELATION_ARG);
    bool        do_mcelem = !PG_ARGISNULL(MOST_COMMON_ELEMS_ARG) &&
        !PG_ARGISNULL(MOST_COMMON_ELEM_FREQS_ARG);
    bool        do_dechist = !PG_ARGISNULL(ELEM_COUNT_HISTOGRAM_ARG);
    bool        do_bounds_histogram = !PG_ARGISNULL(RANGE_BOUNDS_HISTOGRAM_ARG);
    bool        do_range_length_histogram = !PG_ARGISNULL(RANGE_LENGTH_HISTOGRAM_ARG) &&
        !PG_ARGISNULL(RANGE_EMPTY_FRAC_ARG);
 
    Datum       values[Natts_pg_statistic] = {0};
    bool        nulls[Natts_pg_statistic] = {0};
    bool        replaces[Natts_pg_statistic] = {0};
 
    bool        result = true;
 
    stats_check_required_arg(fcinfo, attarginfo, ATTRELATION_ARG);
    reloid = PG_GETARG_OID(ATTRELATION_ARG);
 
    /* lock before looking up attribute */
    stats_lock_check_privileges(reloid);
 
    stats_check_required_arg(fcinfo, attarginfo, ATTNAME_ARG);
    attname = PG_GETARG_NAME(ATTNAME_ARG);
    attnum = get_attnum(reloid, NameStr(*attname));
    if (attnum == InvalidAttrNumber)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" does not exist",
                        NameStr(*attname), get_rel_name(reloid))));
 
    stats_check_required_arg(fcinfo, attarginfo, INHERITED_ARG);
    inherited = PG_GETARG_BOOL(INHERITED_ARG);
 
    /*
     * Check argument sanity. If some arguments are unusable, emit at elevel
     * and set the corresponding argument to NULL in fcinfo.
     */
 
    if (!stats_check_arg_array(fcinfo, attarginfo, MOST_COMMON_FREQS_ARG,
                               elevel))
    {
        do_mcv = false;
        result = false;
    }
 
    if (!stats_check_arg_array(fcinfo, attarginfo, MOST_COMMON_ELEM_FREQS_ARG,
                               elevel))
    {
        do_mcelem = false;
        result = false;
    }
    if (!stats_check_arg_array(fcinfo, attarginfo, ELEM_COUNT_HISTOGRAM_ARG,
                               elevel))
    {
        do_dechist = false;
        result = false;
    }
 
    if (!stats_check_arg_pair(fcinfo, attarginfo,
                              MOST_COMMON_VALS_ARG, MOST_COMMON_FREQS_ARG,
                              elevel))
    {
        do_mcv = false;
        result = false;
    }
 
    if (!stats_check_arg_pair(fcinfo, attarginfo,
                              MOST_COMMON_ELEMS_ARG,
                              MOST_COMMON_ELEM_FREQS_ARG, elevel))
    {
        do_mcelem = false;
        result = false;
    }
 
    if (!stats_check_arg_pair(fcinfo, attarginfo,
                              RANGE_LENGTH_HISTOGRAM_ARG,
                              RANGE_EMPTY_FRAC_ARG, elevel))
    {
        do_range_length_histogram = false;
        result = false;
    }
 
    /* derive information from attribute */
    get_attr_stat_type(reloid, attnum, elevel,
                       &atttypid, &atttypmod,
                       &atttyptype, &atttypcoll,
                       &eq_opr, &lt_opr);
 
    /* if needed, derive element type */
    if (do_mcelem || do_dechist)
    {
        if (!get_elem_stat_type(atttypid, atttyptype, elevel,
                                &elemtypid, &elem_eq_opr))
        {
            ereport(elevel,
                    (errmsg("unable to determine element type of attribute \"%s\"", NameStr(*attname)),
                     errdetail("Cannot set STATISTIC_KIND_MCELEM or STATISTIC_KIND_DECHIST.")));
            elemtypid = InvalidOid;
            elem_eq_opr = InvalidOid;
 
            do_mcelem = false;
            do_dechist = false;
            result = false;
        }
    }
 
    /* histogram and correlation require less-than operator */
    if ((do_histogram || do_correlation) && !OidIsValid(lt_opr))
    {
        ereport(elevel,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("could not determine less-than operator for attribute \"%s\"", NameStr(*attname)),
                 errdetail("Cannot set STATISTIC_KIND_HISTOGRAM or STATISTIC_KIND_CORRELATION.")));
 
        do_histogram = false;
        do_correlation = false;
        result = false;
    }
 
    /* only range types can have range stats */
    if ((do_range_length_histogram || do_bounds_histogram) &&
        !(atttyptype == TYPTYPE_RANGE || atttyptype == TYPTYPE_MULTIRANGE))
    {
        ereport(elevel,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("attribute \"%s\" is not a range type", NameStr(*attname)),
                 errdetail("Cannot set STATISTIC_KIND_RANGE_LENGTH_HISTOGRAM or STATISTIC_KIND_BOUNDS_HISTOGRAM.")));
 
        do_bounds_histogram = false;
        do_range_length_histogram = false;
        result = false;
    }
 
    fmgr_info(F_ARRAY_IN, &array_in_fn);
 
    starel = table_open(StatisticRelationId, RowExclusiveLock);
 
    statup = SearchSysCache3(STATRELATTINH, reloid, attnum, inherited);
 
    /* initialize from existing tuple if exists */
    if (HeapTupleIsValid(statup))
        heap_deform_tuple(statup, RelationGetDescr(starel), values, nulls);
    else
        init_empty_stats_tuple(reloid, attnum, inherited, values, nulls,
                               replaces);
 
    /* if specified, set to argument values */
    if (!PG_ARGISNULL(NULL_FRAC_ARG))
    {
        values[Anum_pg_statistic_stanullfrac - 1] = PG_GETARG_DATUM(NULL_FRAC_ARG);
        replaces[Anum_pg_statistic_stanullfrac - 1] = true;
    }
    if (!PG_ARGISNULL(AVG_WIDTH_ARG))
    {
        values[Anum_pg_statistic_stawidth - 1] = PG_GETARG_DATUM(AVG_WIDTH_ARG);
        replaces[Anum_pg_statistic_stawidth - 1] = true;
    }
    if (!PG_ARGISNULL(N_DISTINCT_ARG))
    {
        values[Anum_pg_statistic_stadistinct - 1] = PG_GETARG_DATUM(N_DISTINCT_ARG);
        replaces[Anum_pg_statistic_stadistinct - 1] = true;
    }
 
    /* STATISTIC_KIND_MCV */
    if (do_mcv)
    {
        bool        converted;
        Datum       stanumbers = PG_GETARG_DATUM(MOST_COMMON_FREQS_ARG);
        Datum       stavalues = text_to_stavalues("most_common_vals",
                                                  &array_in_fn,
                                                  PG_GETARG_DATUM(MOST_COMMON_VALS_ARG),
                                                  atttypid, atttypmod,
                                                  elevel, &converted);
 
        if (converted)
        {
            set_stats_slot(values, nulls, replaces,
                           STATISTIC_KIND_MCV,
                           eq_opr, atttypcoll,
                           stanumbers, false, stavalues, false);
        }
        else
            result = false;
    }
 
    /* STATISTIC_KIND_HISTOGRAM */
    if (do_histogram)
    {
        Datum       stavalues;
        bool        converted = false;
 
        stavalues = text_to_stavalues("histogram_bounds",
                                      &array_in_fn,
                                      PG_GETARG_DATUM(HISTOGRAM_BOUNDS_ARG),
                                      atttypid, atttypmod, elevel,
                                      &converted);
 
        if (converted)
        {
            set_stats_slot(values, nulls, replaces,
                           STATISTIC_KIND_HISTOGRAM,
                           lt_opr, atttypcoll,
                           0, true, stavalues, false);
        }
        else
            result = false;
    }
 
    /* STATISTIC_KIND_CORRELATION */
    if (do_correlation)
    {
        Datum       elems[] = {PG_GETARG_DATUM(CORRELATION_ARG)};
        ArrayType  *arry = construct_array_builtin(elems, 1, FLOAT4OID);
        Datum       stanumbers = PointerGetDatum(arry);
 
        set_stats_slot(values, nulls, replaces,
                       STATISTIC_KIND_CORRELATION,
                       lt_opr, atttypcoll,
                       stanumbers, false, 0, true);
    }
 
    /* STATISTIC_KIND_MCELEM */
    if (do_mcelem)
    {
        Datum       stanumbers = PG_GETARG_DATUM(MOST_COMMON_ELEM_FREQS_ARG);
        bool        converted = false;
        Datum       stavalues;
 
        stavalues = text_to_stavalues("most_common_elems",
                                      &array_in_fn,
                                      PG_GETARG_DATUM(MOST_COMMON_ELEMS_ARG),
                                      elemtypid, atttypmod,
                                      elevel, &converted);
 
        if (converted)
        {
            set_stats_slot(values, nulls, replaces,
                           STATISTIC_KIND_MCELEM,
                           elem_eq_opr, atttypcoll,
                           stanumbers, false, stavalues, false);
        }
        else
            result = false;
    }
 
    /* STATISTIC_KIND_DECHIST */
    if (do_dechist)
    {
        Datum       stanumbers = PG_GETARG_DATUM(ELEM_COUNT_HISTOGRAM_ARG);
 
        set_stats_slot(values, nulls, replaces,
                       STATISTIC_KIND_DECHIST,
                       elem_eq_opr, atttypcoll,
                       stanumbers, false, 0, true);
    }
 
    /*
     * STATISTIC_KIND_BOUNDS_HISTOGRAM
     *
     * This stakind appears before STATISTIC_KIND_RANGE_LENGTH_HISTOGRAM even
     * though it is numerically greater, and all other stakinds appear in
     * numerical order. We duplicate this quirk for consistency.
     */
    if (do_bounds_histogram)
    {
        bool        converted = false;
        Datum       stavalues;
 
        stavalues = text_to_stavalues("range_bounds_histogram",
                                      &array_in_fn,
                                      PG_GETARG_DATUM(RANGE_BOUNDS_HISTOGRAM_ARG),
                                      atttypid, atttypmod,
                                      elevel, &converted);
 
        if (converted)
        {
            set_stats_slot(values, nulls, replaces,
                           STATISTIC_KIND_BOUNDS_HISTOGRAM,
                           InvalidOid, InvalidOid,
                           0, true, stavalues, false);
        }
        else
            result = false;
    }
 
    /* STATISTIC_KIND_RANGE_LENGTH_HISTOGRAM */
    if (do_range_length_histogram)
    {
        /* The anyarray is always a float8[] for this stakind */
        Datum       elems[] = {PG_GETARG_DATUM(RANGE_EMPTY_FRAC_ARG)};
        ArrayType  *arry = construct_array_builtin(elems, 1, FLOAT4OID);
        Datum       stanumbers = PointerGetDatum(arry);
 
        bool        converted = false;
        Datum       stavalues;
 
        stavalues = text_to_stavalues("range_length_histogram",
                                      &array_in_fn,
                                      PG_GETARG_DATUM(RANGE_LENGTH_HISTOGRAM_ARG),
                                      FLOAT8OID, 0, elevel, &converted);
 
        if (converted)
        {
            set_stats_slot(values, nulls, replaces,
                           STATISTIC_KIND_RANGE_LENGTH_HISTOGRAM,
                           Float8LessOperator, InvalidOid,
                           stanumbers, false, stavalues, false);
        }
        else
            result = false;
    }
 
    upsert_pg_statistic(starel, statup, values, nulls, replaces);
 
    if (HeapTupleIsValid(statup))
        ReleaseSysCache(statup);
    table_close(starel, RowExclusiveLock);
 
    return result;
}
 
/*
 * If this relation is an index and that index has expressions in it, and
 * the attnum specified is known to be an expression, then we must walk
 * the list attributes up to the specified attnum to get the right
 * expression.
 */
static Node *
get_attr_expr(Relation rel, int attnum)
{
    if ((rel->rd_rel->relkind == RELKIND_INDEX
         || (rel->rd_rel->relkind == RELKIND_PARTITIONED_INDEX))
        && (rel->rd_indexprs != NIL)
        && (rel->rd_index->indkey.values[attnum - 1] == 0))
    {
        ListCell   *indexpr_item = list_head(rel->rd_indexprs);
 
        for (int i = 0; i < attnum - 1; i++)
            if (rel->rd_index->indkey.values[i] == 0)
                indexpr_item = lnext(rel->rd_indexprs, indexpr_item);
 
        if (indexpr_item == NULL)   /* shouldn't happen */
            elog(ERROR, "too few entries in indexprs list");
 
        return (Node *) lfirst(indexpr_item);
    }
    return NULL;
}
 
/*
 * Derive type information from the attribute.
 */
static void
get_attr_stat_type(Oid reloid, AttrNumber attnum, int elevel,
                   Oid *atttypid, int32 *atttypmod,
                   char *atttyptype, Oid *atttypcoll,
                   Oid *eq_opr, Oid *lt_opr)
{
    Relation    rel = relation_open(reloid, AccessShareLock);
    Form_pg_attribute attr;
    HeapTuple   atup;
    Node       *expr;
    TypeCacheEntry *typcache;
 
    atup = SearchSysCache2(ATTNUM, ObjectIdGetDatum(reloid),
                           Int16GetDatum(attnum));
 
    /* Attribute not found */
    if (!HeapTupleIsValid(atup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("attribute %d of relation \"%s\" does not exist",
                        attnum, RelationGetRelationName(rel))));
 
    attr = (Form_pg_attribute) GETSTRUCT(atup);
 
    if (attr->attisdropped)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("attribute %d of relation \"%s\" does not exist",
                        attnum, RelationGetRelationName(rel))));
 
    expr = get_attr_expr(rel, attr->attnum);
 
    /*
     * When analyzing an expression index, believe the expression tree's type
     * not the column datatype --- the latter might be the opckeytype storage
     * type of the opclass, which is not interesting for our purposes. This
     * mimics the behvior of examine_attribute().
     */
    if (expr == NULL)
    {
        *atttypid = attr->atttypid;
        *atttypmod = attr->atttypmod;
        *atttypcoll = attr->attcollation;
    }
    else
    {
        *atttypid = exprType(expr);
        *atttypmod = exprTypmod(expr);
 
        if (OidIsValid(attr->attcollation))
            *atttypcoll = attr->attcollation;
        else
            *atttypcoll = exprCollation(expr);
    }
    ReleaseSysCache(atup);
 
    /*
     * If it's a multirange, step down to the range type, as is done by
     * multirange_typanalyze().
     */
    if (type_is_multirange(*atttypid))
        *atttypid = get_multirange_range(*atttypid);
 
    /* finds the right operators even if atttypid is a domain */
    typcache = lookup_type_cache(*atttypid, TYPECACHE_LT_OPR | TYPECACHE_EQ_OPR);
    *atttyptype = typcache->typtype;
    *eq_opr = typcache->eq_opr;
    *lt_opr = typcache->lt_opr;
 
    /*
     * Special case: collation for tsvector is DEFAULT_COLLATION_OID. See
     * compute_tsvector_stats().
     */
    if (*atttypid == TSVECTOROID)
        *atttypcoll = DEFAULT_COLLATION_OID;
 
    relation_close(rel, NoLock);
}
 
/*
 * Derive element type information from the attribute type.
 */
static bool
get_elem_stat_type(Oid atttypid, char atttyptype, int elevel,
                   Oid *elemtypid, Oid *elem_eq_opr)
{
    TypeCacheEntry *elemtypcache;
 
    if (atttypid == TSVECTOROID)
    {
        /*
         * Special case: element type for tsvector is text. See
         * compute_tsvector_stats().
         */
        *elemtypid = TEXTOID;
    }
    else
    {
        /* find underlying element type through any domain */
        *elemtypid = get_base_element_type(atttypid);
    }
 
    if (!OidIsValid(*elemtypid))
        return false;
 
    /* finds the right operator even if elemtypid is a domain */
    elemtypcache = lookup_type_cache(*elemtypid, TYPECACHE_EQ_OPR);
    if (!OidIsValid(elemtypcache->eq_opr))
        return false;
 
    *elem_eq_opr = elemtypcache->eq_opr;
 
    return true;
}
 
/*
 * Cast a text datum into an array with element type elemtypid.
 *
 * If an error is encountered, capture it and re-throw at elevel, and set ok
 * to false. If the resulting array contains NULLs, raise an error at elevel
 * and set ok to false. Otherwise, set ok to true.
 */
static Datum
text_to_stavalues(const char *staname, FmgrInfo *array_in, Datum d, Oid typid,
                  int32 typmod, int elevel, bool *ok)
{
    LOCAL_FCINFO(fcinfo, 8);
    char       *s;
    Datum       result;
    ErrorSaveContext escontext = {T_ErrorSaveContext};
 
    escontext.details_wanted = true;
 
    s = TextDatumGetCString(d);
 
    InitFunctionCallInfoData(*fcinfo, array_in, 3, InvalidOid,
                             (Node *) &escontext, NULL);
 
    fcinfo->args[0].value = CStringGetDatum(s);
    fcinfo->args[0].isnull = false;
    fcinfo->args[1].value = ObjectIdGetDatum(typid);
    fcinfo->args[1].isnull = false;
    fcinfo->args[2].value = Int32GetDatum(typmod);
    fcinfo->args[2].isnull = false;
 
    result = FunctionCallInvoke(fcinfo);
 
    pfree(s);
 
    if (escontext.error_occurred)
    {
        if (elevel != ERROR)
            escontext.error_data->elevel = elevel;
        ThrowErrorData(escontext.error_data);
        *ok = false;
        return (Datum) 0;
    }
 
    if (array_contains_nulls(DatumGetArrayTypeP(result)))
    {
        ereport(elevel,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("\"%s\" array cannot contain NULL values", staname)));
        *ok = false;
        return (Datum) 0;
    }
 
    *ok = true;
 
    return result;
}
 
/*
 * Find and update the slot with the given stakind, or use the first empty
 * slot.
 */
static void
set_stats_slot(Datum *values, bool *nulls, bool *replaces,
               int16 stakind, Oid staop, Oid stacoll,
               Datum stanumbers, bool stanumbers_isnull,
               Datum stavalues, bool stavalues_isnull)
{
    int         slotidx;
    int         first_empty = -1;
    AttrNumber  stakind_attnum;
    AttrNumber  staop_attnum;
    AttrNumber  stacoll_attnum;
 
    /* find existing slot with given stakind */
    for (slotidx = 0; slotidx < STATISTIC_NUM_SLOTS; slotidx++)
    {
        stakind_attnum = Anum_pg_statistic_stakind1 - 1 + slotidx;
 
        if (first_empty < 0 &&
            DatumGetInt16(values[stakind_attnum]) == 0)
            first_empty = slotidx;
        if (DatumGetInt16(values[stakind_attnum]) == stakind)
            break;
    }
 
    if (slotidx >= STATISTIC_NUM_SLOTS && first_empty >= 0)
        slotidx = first_empty;
 
    if (slotidx >= STATISTIC_NUM_SLOTS)
        ereport(ERROR,
                (errmsg("maximum number of statistics slots exceeded: %d",
                        slotidx + 1)));
 
    stakind_attnum = Anum_pg_statistic_stakind1 - 1 + slotidx;
    staop_attnum = Anum_pg_statistic_staop1 - 1 + slotidx;
    stacoll_attnum = Anum_pg_statistic_stacoll1 - 1 + slotidx;
 
    if (DatumGetInt16(values[stakind_attnum]) != stakind)
    {
        values[stakind_attnum] = Int16GetDatum(stakind);
        replaces[stakind_attnum] = true;
    }
    if (DatumGetObjectId(values[staop_attnum]) != staop)
    {
        values[staop_attnum] = ObjectIdGetDatum(staop);
        replaces[staop_attnum] = true;
    }
    if (DatumGetObjectId(values[stacoll_attnum]) != stacoll)
    {
        values[stacoll_attnum] = ObjectIdGetDatum(stacoll);
        replaces[stacoll_attnum] = true;
    }
    if (!stanumbers_isnull)
    {
        values[Anum_pg_statistic_stanumbers1 - 1 + slotidx] = stanumbers;
        nulls[Anum_pg_statistic_stanumbers1 - 1 + slotidx] = false;
        replaces[Anum_pg_statistic_stanumbers1 - 1 + slotidx] = true;
    }
    if (!stavalues_isnull)
    {
        values[Anum_pg_statistic_stavalues1 - 1 + slotidx] = stavalues;
        nulls[Anum_pg_statistic_stavalues1 - 1 + slotidx] = false;
        replaces[Anum_pg_statistic_stavalues1 - 1 + slotidx] = true;
    }
}
 
/*
 * Upsert the pg_statistic record.
 */
static void
upsert_pg_statistic(Relation starel, HeapTuple oldtup,
                    Datum *values, bool *nulls, bool *replaces)
{
    HeapTuple   newtup;
 
    if (HeapTupleIsValid(oldtup))
    {
        newtup = heap_modify_tuple(oldtup, RelationGetDescr(starel),
                                   values, nulls, replaces);
        CatalogTupleUpdate(starel, &newtup->t_self, newtup);
    }
    else
    {
        newtup = heap_form_tuple(RelationGetDescr(starel), values, nulls);
        CatalogTupleInsert(starel, newtup);
    }
 
    heap_freetuple(newtup);
}
 
/*
 * Delete pg_statistic record.
 */
static bool
delete_pg_statistic(Oid reloid, AttrNumber attnum, bool stainherit)
{
    Relation    sd = table_open(StatisticRelationId, RowExclusiveLock);
    HeapTuple   oldtup;
 
    /* Is there already a pg_statistic tuple for this attribute? */
    oldtup = SearchSysCache3(STATRELATTINH,
                             ObjectIdGetDatum(reloid),
                             Int16GetDatum(attnum),
                             BoolGetDatum(stainherit));
 
    if (HeapTupleIsValid(oldtup))
    {
        CatalogTupleDelete(sd, &oldtup->t_self);
        ReleaseSysCache(oldtup);
        table_close(sd, RowExclusiveLock);
        return true;
    }
 
    table_close(sd, RowExclusiveLock);
    return false;
}
 
/*
 * Initialize values and nulls for a new stats tuple.
 */
static void
init_empty_stats_tuple(Oid reloid, int16 attnum, bool inherited,
                       Datum *values, bool *nulls, bool *replaces)
{
    memset(nulls, true, sizeof(bool) * Natts_pg_statistic);
    memset(replaces, true, sizeof(bool) * Natts_pg_statistic);
 
    /* must initialize non-NULL attributes */
 
    values[Anum_pg_statistic_starelid - 1] = ObjectIdGetDatum(reloid);
    nulls[Anum_pg_statistic_starelid - 1] = false;
    values[Anum_pg_statistic_staattnum - 1] = Int16GetDatum(attnum);
    nulls[Anum_pg_statistic_staattnum - 1] = false;
    values[Anum_pg_statistic_stainherit - 1] = BoolGetDatum(inherited);
    nulls[Anum_pg_statistic_stainherit - 1] = false;
 
    values[Anum_pg_statistic_stanullfrac - 1] = DEFAULT_NULL_FRAC;
    nulls[Anum_pg_statistic_stanullfrac - 1] = false;
    values[Anum_pg_statistic_stawidth - 1] = DEFAULT_AVG_WIDTH;
    nulls[Anum_pg_statistic_stawidth - 1] = false;
    values[Anum_pg_statistic_stadistinct - 1] = DEFAULT_N_DISTINCT;
    nulls[Anum_pg_statistic_stadistinct - 1] = false;
 
    /* initialize stakind, staop, and stacoll slots */
    for (int slotnum = 0; slotnum < STATISTIC_NUM_SLOTS; slotnum++)
    {
        values[Anum_pg_statistic_stakind1 + slotnum - 1] = (Datum) 0;
        nulls[Anum_pg_statistic_stakind1 + slotnum - 1] = false;
        values[Anum_pg_statistic_staop1 + slotnum - 1] = InvalidOid;
        nulls[Anum_pg_statistic_staop1 + slotnum - 1] = false;
        values[Anum_pg_statistic_stacoll1 + slotnum - 1] = InvalidOid;
        nulls[Anum_pg_statistic_stacoll1 + slotnum - 1] = false;
    }
}
 
/*
 * Import statistics for a given relation attribute.
 *
 * Inserts or replaces a row in pg_statistic for the given relation and
 * attribute name. It takes input parameters that correspond to columns in the
 * view pg_stats.
 *
 * Parameters null_frac, avg_width, and n_distinct all correspond to NOT NULL
 * columns in pg_statistic. The remaining parameters all belong to a specific
 * stakind. Some stakinds require multiple parameters, which must be specified
 * together (or neither specified).
 *
 * Parameters are only superficially validated. Omitting a parameter or
 * passing NULL leaves the statistic unchanged.
 *
 * Parameters corresponding to ANYARRAY columns are instead passed in as text
 * values, which is a valid input string for an array of the type or element
 * type of the attribute. Any error generated by the array_in() function will
 * in turn fail the function.
 */
Datum
pg_set_attribute_stats(PG_FUNCTION_ARGS)
{
    attribute_statistics_update(fcinfo, ERROR);
    PG_RETURN_VOID();
}
 
/*
 * Delete statistics for the given attribute.
 */
Datum
pg_clear_attribute_stats(PG_FUNCTION_ARGS)
{
    Oid         reloid;
    Name        attname;
    AttrNumber  attnum;
    bool        inherited;
 
    stats_check_required_arg(fcinfo, attarginfo, ATTRELATION_ARG);
    reloid = PG_GETARG_OID(ATTRELATION_ARG);
 
    stats_lock_check_privileges(reloid);
 
    stats_check_required_arg(fcinfo, attarginfo, ATTNAME_ARG);
    attname = PG_GETARG_NAME(ATTNAME_ARG);
    attnum = get_attnum(reloid, NameStr(*attname));
    if (attnum == InvalidAttrNumber)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" does not exist",
                        NameStr(*attname), get_rel_name(reloid))));
 
    stats_check_required_arg(fcinfo, attarginfo, INHERITED_ARG);
    inherited = PG_GETARG_BOOL(INHERITED_ARG);
 
    delete_pg_statistic(reloid, attnum, inherited);
    PG_RETURN_VOID();
}