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           2 : 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           4 : PG_FUNCTION_INFO_V1(pg_freespace);
      26             : 
      27             : Datum
      28          94 : pg_freespace(PG_FUNCTION_ARGS)
      29             : {
      30          94 :     Oid         relid = PG_GETARG_OID(0);
      31          94 :     int64       blkno = PG_GETARG_INT64(1);
      32             :     int16       freespace;
      33             :     Relation    rel;
      34             : 
      35          94 :     rel = relation_open(relid, AccessShareLock);
      36             : 
      37          94 :     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          94 :     if (blkno < 0 || blkno > MaxBlockNumber)
      45           4 :         ereport(ERROR,
      46             :                 (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
      47             :                  errmsg("invalid block number")));
      48             : 
      49          90 :     freespace = GetRecordedFreeSpace(rel, blkno);
      50             : 
      51          90 :     relation_close(rel, AccessShareLock);
      52          90 :     PG_RETURN_INT16(freespace);
      53             : }