pgstatindex.c

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/*
 * contrib/pgstattuple/pgstatindex.c
 *
 *
 * pgstatindex
 *
 * Copyright (c) 2006 Satoshi Nagayasu <nagayasus@nttdata.co.jp>
 *
 * Permission to use, copy, modify, and distribute this software and
 * its documentation for any purpose, without fee, and without a
 * written agreement is hereby granted, provided that the above
 * copyright notice and this paragraph and the following two
 * paragraphs appear in all copies.
 *
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE TO ANY PARTY FOR DIRECT,
 * INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
 * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
 * DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * THE AUTHOR SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS
 * IS" BASIS, AND THE AUTHOR HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE,
 * SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 */
 
#include "postgres.h"
 
#include "access/gin_private.h"
#include "access/hash.h"
#include "access/htup_details.h"
#include "access/nbtree.h"
#include "access/relation.h"
#include "access/table.h"
#include "catalog/namespace.h"
#include "catalog/pg_am.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "storage/lmgr.h"
#include "utils/builtins.h"
#include "utils/rel.h"
#include "utils/varlena.h"
 
 
/*
 * Because of backward-compatibility issue, we have decided to have
 * two types of interfaces, with regclass-type input arg and text-type
 * input arg, for each function.
 *
 * Those functions which have text-type input arg will be deprecated
 * in the future release.
 */
PG_FUNCTION_INFO_V1(pgstatindex);
PG_FUNCTION_INFO_V1(pgstatindexbyid);
PG_FUNCTION_INFO_V1(pg_relpages);
PG_FUNCTION_INFO_V1(pg_relpagesbyid);
PG_FUNCTION_INFO_V1(pgstatginindex);
PG_FUNCTION_INFO_V1(pgstathashindex);
 
PG_FUNCTION_INFO_V1(pgstatindex_v1_5);
PG_FUNCTION_INFO_V1(pgstatindexbyid_v1_5);
PG_FUNCTION_INFO_V1(pg_relpages_v1_5);
PG_FUNCTION_INFO_V1(pg_relpagesbyid_v1_5);
PG_FUNCTION_INFO_V1(pgstatginindex_v1_5);
 
Datum       pgstatginindex_internal(Oid relid, FunctionCallInfo fcinfo);
 
#define IS_INDEX(r) ((r)->rd_rel->relkind == RELKIND_INDEX)
#define IS_BTREE(r) ((r)->rd_rel->relam == BTREE_AM_OID)
#define IS_GIN(r) ((r)->rd_rel->relam == GIN_AM_OID)
#define IS_HASH(r) ((r)->rd_rel->relam == HASH_AM_OID)
 
/* ------------------------------------------------
 * A structure for a whole btree index statistics
 * used by pgstatindex().
 * ------------------------------------------------
 */
typedef struct BTIndexStat
{
    uint32      version;
    uint32      level;
    BlockNumber root_blkno;
 
    uint64      internal_pages;
    uint64      leaf_pages;
    uint64      empty_pages;
    uint64      deleted_pages;
 
    uint64      max_avail;
    uint64      free_space;
 
    uint64      fragments;
} BTIndexStat;
 
/* ------------------------------------------------
 * A structure for a whole GIN index statistics
 * used by pgstatginindex().
 * ------------------------------------------------
 */
typedef struct GinIndexStat
{
    int32       version;
 
    BlockNumber pending_pages;
    int64       pending_tuples;
} GinIndexStat;
 
/* ------------------------------------------------
 * A structure for a whole HASH index statistics
 * used by pgstathashindex().
 * ------------------------------------------------
 */
typedef struct HashIndexStat
{
    int32       version;
    int32       space_per_page;
 
    BlockNumber bucket_pages;
    BlockNumber overflow_pages;
    BlockNumber bitmap_pages;
    BlockNumber unused_pages;
 
    int64       live_items;
    int64       dead_items;
    uint64      free_space;
} HashIndexStat;
 
static Datum pgstatindex_impl(Relation rel, FunctionCallInfo fcinfo);
static int64 pg_relpages_impl(Relation rel);
static void GetHashPageStats(Page page, HashIndexStat *stats);
 
/* ------------------------------------------------------
 * pgstatindex()
 *
 * Usage: SELECT * FROM pgstatindex('t1_pkey');
 *
 * The superuser() check here must be kept as the library might be upgraded
 * without the extension being upgraded, meaning that in pre-1.5 installations
 * these functions could be called by any user.
 * ------------------------------------------------------
 */
Datum
pgstatindex(PG_FUNCTION_ARGS)
{
    text       *relname = PG_GETARG_TEXT_PP(0);
    Relation    rel;
    RangeVar   *relrv;
 
    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be superuser to use pgstattuple functions")));
 
    relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
    rel = relation_openrv(relrv, AccessShareLock);
 
    PG_RETURN_DATUM(pgstatindex_impl(rel, fcinfo));
}
 
/*
 * As of pgstattuple version 1.5, we no longer need to check if the user
 * is a superuser because we REVOKE EXECUTE on the function from PUBLIC.
 * Users can then grant access to it based on their policies.
 *
 * Otherwise identical to pgstatindex (above).
 */
Datum
pgstatindex_v1_5(PG_FUNCTION_ARGS)
{
    text       *relname = PG_GETARG_TEXT_PP(0);
    Relation    rel;
    RangeVar   *relrv;
 
    relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
    rel = relation_openrv(relrv, AccessShareLock);
 
    PG_RETURN_DATUM(pgstatindex_impl(rel, fcinfo));
}
 
/*
 * The superuser() check here must be kept as the library might be upgraded
 * without the extension being upgraded, meaning that in pre-1.5 installations
 * these functions could be called by any user.
 */
Datum
pgstatindexbyid(PG_FUNCTION_ARGS)
{
    Oid         relid = PG_GETARG_OID(0);
    Relation    rel;
 
    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be superuser to use pgstattuple functions")));
 
    rel = relation_open(relid, AccessShareLock);
 
    PG_RETURN_DATUM(pgstatindex_impl(rel, fcinfo));
}
 
/* No need for superuser checks in v1.5, see above */
Datum
pgstatindexbyid_v1_5(PG_FUNCTION_ARGS)
{
    Oid         relid = PG_GETARG_OID(0);
    Relation    rel;
 
    rel = relation_open(relid, AccessShareLock);
 
    PG_RETURN_DATUM(pgstatindex_impl(rel, fcinfo));
}
 
static Datum
pgstatindex_impl(Relation rel, FunctionCallInfo fcinfo)
{
    Datum       result;
    BlockNumber nblocks;
    BlockNumber blkno;
    BTIndexStat indexStat;
    BufferAccessStrategy bstrategy = GetAccessStrategy(BAS_BULKREAD);
 
    if (!IS_INDEX(rel) || !IS_BTREE(rel))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("relation \"%s\" is not a btree index",
                        RelationGetRelationName(rel))));
 
    /*
     * Reject attempts to read non-local temporary relations; we would be
     * likely to get wrong data since we have no visibility into the owning
     * session's local buffers.
     */
    if (RELATION_IS_OTHER_TEMP(rel))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot access temporary tables of other sessions")));
 
    /*
     * Read metapage
     */
    {
        Buffer      buffer = ReadBufferExtended(rel, MAIN_FORKNUM, 0, RBM_NORMAL, bstrategy);
        Page        page = BufferGetPage(buffer);
        BTMetaPageData *metad = BTPageGetMeta(page);
 
        indexStat.version = metad->btm_version;
        indexStat.level = metad->btm_level;
        indexStat.root_blkno = metad->btm_root;
 
        ReleaseBuffer(buffer);
    }
 
    /* -- init counters -- */
    indexStat.internal_pages = 0;
    indexStat.leaf_pages = 0;
    indexStat.empty_pages = 0;
    indexStat.deleted_pages = 0;
 
    indexStat.max_avail = 0;
    indexStat.free_space = 0;
 
    indexStat.fragments = 0;
 
    /*
     * Scan all blocks except the metapage
     */
    nblocks = RelationGetNumberOfBlocks(rel);
 
    for (blkno = 1; blkno < nblocks; blkno++)
    {
        Buffer      buffer;
        Page        page;
        BTPageOpaque opaque;
 
        CHECK_FOR_INTERRUPTS();
 
        /* Read and lock buffer */
        buffer = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL, bstrategy);
        LockBuffer(buffer, BUFFER_LOCK_SHARE);
 
        page = BufferGetPage(buffer);
        opaque = BTPageGetOpaque(page);
 
        /*
         * Determine page type, and update totals.
         *
         * Note that we arbitrarily bucket deleted pages together without
         * considering if they're leaf pages or internal pages.
         */
        if (P_ISDELETED(opaque))
            indexStat.deleted_pages++;
        else if (P_IGNORE(opaque))
            indexStat.empty_pages++;    /* this is the "half dead" state */
        else if (P_ISLEAF(opaque))
        {
            int         max_avail;
 
            max_avail = BLCKSZ - (BLCKSZ - ((PageHeader) page)->pd_special + SizeOfPageHeaderData);
            indexStat.max_avail += max_avail;
            indexStat.free_space += PageGetFreeSpace(page);
 
            indexStat.leaf_pages++;
 
            /*
             * If the next leaf is on an earlier block, it means a
             * fragmentation.
             */
            if (opaque->btpo_next != P_NONE && opaque->btpo_next < blkno)
                indexStat.fragments++;
        }
        else
            indexStat.internal_pages++;
 
        /* Unlock and release buffer */
        LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
        ReleaseBuffer(buffer);
    }
 
    relation_close(rel, AccessShareLock);
 
    /*----------------------------
     * Build a result tuple
     *----------------------------
     */
    {
        TupleDesc   tupleDesc;
        int         j;
        char       *values[10];
        HeapTuple   tuple;
 
        /* Build a tuple descriptor for our result type */
        if (get_call_result_type(fcinfo, NULL, &tupleDesc) != TYPEFUNC_COMPOSITE)
            elog(ERROR, "return type must be a row type");
 
        j = 0;
        values[j++] = psprintf("%d", indexStat.version);
        values[j++] = psprintf("%d", indexStat.level);
        values[j++] = psprintf(INT64_FORMAT,
                               (1 + /* include the metapage in index_size */
                                indexStat.leaf_pages +
                                indexStat.internal_pages +
                                indexStat.deleted_pages +
                                indexStat.empty_pages) * BLCKSZ);
        values[j++] = psprintf("%u", indexStat.root_blkno);
        values[j++] = psprintf(INT64_FORMAT, indexStat.internal_pages);
        values[j++] = psprintf(INT64_FORMAT, indexStat.leaf_pages);
        values[j++] = psprintf(INT64_FORMAT, indexStat.empty_pages);
        values[j++] = psprintf(INT64_FORMAT, indexStat.deleted_pages);
        if (indexStat.max_avail > 0)
            values[j++] = psprintf("%.2f",
                                   100.0 - (double) indexStat.free_space / (double) indexStat.max_avail * 100.0);
        else
            values[j++] = pstrdup("NaN");
        if (indexStat.leaf_pages > 0)
            values[j++] = psprintf("%.2f",
                                   (double) indexStat.fragments / (double) indexStat.leaf_pages * 100.0);
        else
            values[j++] = pstrdup("NaN");
 
        tuple = BuildTupleFromCStrings(TupleDescGetAttInMetadata(tupleDesc),
                                       values);
 
        result = HeapTupleGetDatum(tuple);
    }
 
    return result;
}
 
/* --------------------------------------------------------
 * pg_relpages()
 *
 * Get the number of pages of the table/index.
 *
 * Usage: SELECT pg_relpages('t1');
 *        SELECT pg_relpages('t1_pkey');
 *
 * Must keep superuser() check, see above.
 * --------------------------------------------------------
 */
Datum
pg_relpages(PG_FUNCTION_ARGS)
{
    text       *relname = PG_GETARG_TEXT_PP(0);
    Relation    rel;
    RangeVar   *relrv;
 
    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be superuser to use pgstattuple functions")));
 
    relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
    rel = relation_openrv(relrv, AccessShareLock);
 
    PG_RETURN_INT64(pg_relpages_impl(rel));
}
 
/* No need for superuser checks in v1.5, see above */
Datum
pg_relpages_v1_5(PG_FUNCTION_ARGS)
{
    text       *relname = PG_GETARG_TEXT_PP(0);
    Relation    rel;
    RangeVar   *relrv;
 
    relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
    rel = relation_openrv(relrv, AccessShareLock);
 
    PG_RETURN_INT64(pg_relpages_impl(rel));
}
 
/* Must keep superuser() check, see above. */
Datum
pg_relpagesbyid(PG_FUNCTION_ARGS)
{
    Oid         relid = PG_GETARG_OID(0);
    Relation    rel;
 
    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be superuser to use pgstattuple functions")));
 
    rel = relation_open(relid, AccessShareLock);
 
    PG_RETURN_INT64(pg_relpages_impl(rel));
}
 
/* No need for superuser checks in v1.5, see above */
Datum
pg_relpagesbyid_v1_5(PG_FUNCTION_ARGS)
{
    Oid         relid = PG_GETARG_OID(0);
    Relation    rel;
 
    rel = relation_open(relid, AccessShareLock);
 
    PG_RETURN_INT64(pg_relpages_impl(rel));
}
 
static int64
pg_relpages_impl(Relation rel)
{
    int64       relpages;
 
    if (!RELKIND_HAS_STORAGE(rel->rd_rel->relkind))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot get page count of relation \"%s\"",
                        RelationGetRelationName(rel)),
                 errdetail_relkind_not_supported(rel->rd_rel->relkind)));
 
    /* note: this will work OK on non-local temp tables */
 
    relpages = RelationGetNumberOfBlocks(rel);
 
    relation_close(rel, AccessShareLock);
 
    return relpages;
}
 
/* ------------------------------------------------------
 * pgstatginindex()
 *
 * Usage: SELECT * FROM pgstatginindex('ginindex');
 *
 * Must keep superuser() check, see above.
 * ------------------------------------------------------
 */
Datum
pgstatginindex(PG_FUNCTION_ARGS)
{
    Oid         relid = PG_GETARG_OID(0);
 
    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be superuser to use pgstattuple functions")));
 
    PG_RETURN_DATUM(pgstatginindex_internal(relid, fcinfo));
}
 
/* No need for superuser checks in v1.5, see above */
Datum
pgstatginindex_v1_5(PG_FUNCTION_ARGS)
{
    Oid         relid = PG_GETARG_OID(0);
 
    PG_RETURN_DATUM(pgstatginindex_internal(relid, fcinfo));
}
 
Datum
pgstatginindex_internal(Oid relid, FunctionCallInfo fcinfo)
{
    Relation    rel;
    Buffer      buffer;
    Page        page;
    GinMetaPageData *metadata;
    GinIndexStat stats;
    HeapTuple   tuple;
    TupleDesc   tupleDesc;
    Datum       values[3];
    bool        nulls[3] = {false, false, false};
    Datum       result;
 
    rel = relation_open(relid, AccessShareLock);
 
    if (!IS_INDEX(rel) || !IS_GIN(rel))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("relation \"%s\" is not a GIN index",
                        RelationGetRelationName(rel))));
 
    /*
     * Reject attempts to read non-local temporary relations; we would be
     * likely to get wrong data since we have no visibility into the owning
     * session's local buffers.
     */
    if (RELATION_IS_OTHER_TEMP(rel))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot access temporary indexes of other sessions")));
 
    /*
     * Read metapage
     */
    buffer = ReadBuffer(rel, GIN_METAPAGE_BLKNO);
    LockBuffer(buffer, GIN_SHARE);
    page = BufferGetPage(buffer);
    metadata = GinPageGetMeta(page);
 
    stats.version = metadata->ginVersion;
    stats.pending_pages = metadata->nPendingPages;
    stats.pending_tuples = metadata->nPendingHeapTuples;
 
    UnlockReleaseBuffer(buffer);
    relation_close(rel, AccessShareLock);
 
    /*
     * Build a tuple descriptor for our result type
     */
    if (get_call_result_type(fcinfo, NULL, &tupleDesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");
 
    values[0] = Int32GetDatum(stats.version);
    values[1] = UInt32GetDatum(stats.pending_pages);
    values[2] = Int64GetDatum(stats.pending_tuples);
 
    /*
     * Build and return the tuple
     */
    tuple = heap_form_tuple(tupleDesc, values, nulls);
    result = HeapTupleGetDatum(tuple);
 
    return result;
}
 
/* ------------------------------------------------------
 * pgstathashindex()
 *
 * Usage: SELECT * FROM pgstathashindex('hashindex');
 * ------------------------------------------------------
 */
Datum
pgstathashindex(PG_FUNCTION_ARGS)
{
    Oid         relid = PG_GETARG_OID(0);
    BlockNumber nblocks;
    BlockNumber blkno;
    Relation    rel;
    HashIndexStat stats;
    BufferAccessStrategy bstrategy;
    HeapTuple   tuple;
    TupleDesc   tupleDesc;
    Datum       values[8];
    bool        nulls[8] = {0};
    Buffer      metabuf;
    HashMetaPage metap;
    float8      free_percent;
    uint64      total_space;
 
    rel = index_open(relid, AccessShareLock);
 
    /* index_open() checks that it's an index */
    if (!IS_HASH(rel))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("relation \"%s\" is not a hash index",
                        RelationGetRelationName(rel))));
 
    /*
     * Reject attempts to read non-local temporary relations; we would be
     * likely to get wrong data since we have no visibility into the owning
     * session's local buffers.
     */
    if (RELATION_IS_OTHER_TEMP(rel))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot access temporary indexes of other sessions")));
 
    /* Get the information we need from the metapage. */
    memset(&stats, 0, sizeof(stats));
    metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_READ, LH_META_PAGE);
    metap = HashPageGetMeta(BufferGetPage(metabuf));
    stats.version = metap->hashm_version;
    stats.space_per_page = metap->hashm_bsize;
    _hash_relbuf(rel, metabuf);
 
    /* Get the current relation length */
    nblocks = RelationGetNumberOfBlocks(rel);
 
    /* prepare access strategy for this index */
    bstrategy = GetAccessStrategy(BAS_BULKREAD);
 
    /* Start from blkno 1 as 0th block is metapage */
    for (blkno = 1; blkno < nblocks; blkno++)
    {
        Buffer      buf;
        Page        page;
 
        CHECK_FOR_INTERRUPTS();
 
        buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
                                 bstrategy);
        LockBuffer(buf, BUFFER_LOCK_SHARE);
        page = (Page) BufferGetPage(buf);
 
        if (PageIsNew(page))
            stats.unused_pages++;
        else if (PageGetSpecialSize(page) !=
                 MAXALIGN(sizeof(HashPageOpaqueData)))
            ereport(ERROR,
                    (errcode(ERRCODE_INDEX_CORRUPTED),
                     errmsg("index \"%s\" contains corrupted page at block %u",
                            RelationGetRelationName(rel),
                            BufferGetBlockNumber(buf))));
        else
        {
            HashPageOpaque opaque;
            int         pagetype;
 
            opaque = HashPageGetOpaque(page);
            pagetype = opaque->hasho_flag & LH_PAGE_TYPE;
 
            if (pagetype == LH_BUCKET_PAGE)
            {
                stats.bucket_pages++;
                GetHashPageStats(page, &stats);
            }
            else if (pagetype == LH_OVERFLOW_PAGE)
            {
                stats.overflow_pages++;
                GetHashPageStats(page, &stats);
            }
            else if (pagetype == LH_BITMAP_PAGE)
                stats.bitmap_pages++;
            else if (pagetype == LH_UNUSED_PAGE)
                stats.unused_pages++;
            else
                ereport(ERROR,
                        (errcode(ERRCODE_INDEX_CORRUPTED),
                         errmsg("unexpected page type 0x%04X in HASH index \"%s\" block %u",
                                opaque->hasho_flag, RelationGetRelationName(rel),
                                BufferGetBlockNumber(buf))));
        }
        UnlockReleaseBuffer(buf);
    }
 
    /* Done accessing the index */
    index_close(rel, AccessShareLock);
 
    /* Count unused pages as free space. */
    stats.free_space += (uint64) stats.unused_pages * stats.space_per_page;
 
    /*
     * Total space available for tuples excludes the metapage and the bitmap
     * pages.
     */
    total_space = (uint64) (nblocks - (stats.bitmap_pages + 1)) *
        stats.space_per_page;
 
    if (total_space == 0)
        free_percent = 0.0;
    else
        free_percent = 100.0 * stats.free_space / total_space;
 
    /*
     * Build a tuple descriptor for our result type
     */
    if (get_call_result_type(fcinfo, NULL, &tupleDesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");
 
    tupleDesc = BlessTupleDesc(tupleDesc);
 
    /*
     * Build and return the tuple
     */
    values[0] = Int32GetDatum(stats.version);
    values[1] = Int64GetDatum((int64) stats.bucket_pages);
    values[2] = Int64GetDatum((int64) stats.overflow_pages);
    values[3] = Int64GetDatum((int64) stats.bitmap_pages);
    values[4] = Int64GetDatum((int64) stats.unused_pages);
    values[5] = Int64GetDatum(stats.live_items);
    values[6] = Int64GetDatum(stats.dead_items);
    values[7] = Float8GetDatum(free_percent);
    tuple = heap_form_tuple(tupleDesc, values, nulls);
 
    PG_RETURN_DATUM(HeapTupleGetDatum(tuple));
}
 
/* -------------------------------------------------
 * GetHashPageStats()
 *
 * Collect statistics of single hash page
 * -------------------------------------------------
 */
static void
GetHashPageStats(Page page, HashIndexStat *stats)
{
    OffsetNumber maxoff = PageGetMaxOffsetNumber(page);
    int         off;
 
    /* count live and dead tuples, and free space */
    for (off = FirstOffsetNumber; off <= maxoff; off++)
    {
        ItemId      id = PageGetItemId(page, off);
 
        if (!ItemIdIsDead(id))
            stats->live_items++;
        else
            stats->dead_items++;
    }
    stats->free_space += PageGetExactFreeSpace(page);
}