contrib/pg_freespacemap/pg_freespacemap.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * pg_freespacemap.c
   4  *        display contents of a free space map
   5  *
   6  *        $PostgreSQL$
   7  *-------------------------------------------------------------------------
   8  */
   9 #include "postgres.h"
  10
  11 #include "access/heapam.h"
  12 #include "funcapi.h"
  13 #include "storage/block.h"
  14 #include "storage/freespace.h"
  15
  16
  17 PG_MODULE_MAGIC;
  18
  19 Datum           pg_freespace(PG_FUNCTION_ARGS);
  20
  21 /*
  22  * Returns the amount of free space on a given page, according to the
  23  * free space map.
  24  */
  25 PG_FUNCTION_INFO_V1(pg_freespace);
  26
  27 Datum
  28 pg_freespace(PG_FUNCTION_ARGS)
  29 {
  30         Oid             relid = PG_GETARG_OID(0);
  31         int64   blkno = PG_GETARG_INT64(1);
  32         int16   freespace;
  33         Relation rel;
  34
  35         rel = relation_open(relid, AccessShareLock);
  36
  37         if (blkno < 0 || blkno > MaxBlockNumber)
  38                 ereport(ERROR,
  39                                 (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
  40                                  errmsg("invalid block number")));
  41
  42         freespace = GetRecordedFreeSpace(rel, blkno);
  43
  44         relation_close(rel, AccessShareLock);
  45         PG_RETURN_INT16(freespace);
  46 }