granicus.if.org Git - postgresql/blob - contrib/pg_freespacemap/pg_freespacemap.c

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