pg_freespacemap.c

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/*-------------------------------------------------------------------------
 *
 * pg_freespacemap.c
 *    display contents of a free space map
 *
 *    contrib/pg_freespacemap/pg_freespacemap.c
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "funcapi.h"
#include "storage/freespace.h"


PG_MODULE_MAGIC;

Datum       pg_freespace(PG_FUNCTION_ARGS);

/*
 * Returns the amount of free space on a given page, according to the
 * free space map.
 */
PG_FUNCTION_INFO_V1(pg_freespace);

Datum
pg_freespace(PG_FUNCTION_ARGS)
{
    Oid         relid = PG_GETARG_OID(0);
    int64       blkno = PG_GETARG_INT64(1);
    int16       freespace;
    Relation    rel;

    rel = relation_open(relid, AccessShareLock);

    if (blkno < 0 || blkno > MaxBlockNumber)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid block number")));

    freespace = GetRecordedFreeSpace(rel, blkno);

    relation_close(rel, AccessShareLock);
    PG_RETURN_INT16(freespace);
}