Line data    Source code

       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 "fmgr.h"
      13              : #include "storage/freespace.h"
      14              : #include "utils/rel.h"
      15              : 
      16            1 : PG_MODULE_MAGIC_EXT(
      17              :                     .name = "pg_freespacemap",
      18              :                     .version = PG_VERSION
      19              : );
      20              : 
      21              : /*
      22              :  * Returns the amount of free space on a given page, according to the
      23              :  * free space map.
      24              :  */
      25            2 : PG_FUNCTION_INFO_V1(pg_freespace);
      26              : 
      27              : Datum
      28           47 : pg_freespace(PG_FUNCTION_ARGS)
      29              : {
      30           47 :     Oid         relid = PG_GETARG_OID(0);
      31           47 :     int64       blkno = PG_GETARG_INT64(1);
      32              :     int16       freespace;
      33              :     Relation    rel;
      34              : 
      35           47 :     rel = relation_open(relid, AccessShareLock);
      36              : 
      37           47 :     if (!RELKIND_HAS_STORAGE(rel->rd_rel->relkind))
      38            0 :         ereport(ERROR,
      39              :                 (errcode(ERRCODE_WRONG_OBJECT_TYPE),
      40              :                  errmsg("relation \"%s\" does not have storage",
      41              :                         RelationGetRelationName(rel)),
      42              :                  errdetail_relkind_not_supported(rel->rd_rel->relkind)));
      43              : 
      44           47 :     if (blkno < 0 || blkno > MaxBlockNumber)
      45            2 :         ereport(ERROR,
      46              :                 (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
      47              :                  errmsg("invalid block number")));
      48              : 
      49           45 :     freespace = GetRecordedFreeSpace(rel, blkno);
      50              : 
      51           45 :     relation_close(rel, AccessShareLock);
      52           45 :     PG_RETURN_INT16(freespace);
      53              : }