pl sql procedure to reclaim space in a datafile

This procedure can quickly help to reclaim space above the HWM in a datafile

CREATE OR REPLACE PROCEDURE reclaim_datafile_space (fileid NUMBER)
IS
   taille       NUMBER;
   block_size   INTEGER;
BEGIN
   SELECT VALUE
     INTO block_size
     FROM V$PARAMETER
    WHERE NAME = 'db_block_size';

   SELECT CEIL ( (highblock * block_size + block_size) / 1024)
     INTO taille
     FROM (  SELECT file_id, MAX (block_id + blocks) highblock
               FROM dba_extents
              WHERE file_id = fileid
           GROUP BY file_id);

   EXECUTE IMMEDIATE
      'alter database datafile ' || fileid || ' resize ' || taille || 'K';
END;
/

It is based on Tanel Poder script trim_database