text: -- @Description Ensures that a serializable select before during a vacuum operation avoids the compaction.
  -- 
  
  DELETE FROM ao WHERE a < 128;
  1: BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
  1: SELECT COUNT(*) FROM ao;
  2: VACUUM ao;
  1: SELECT COUNT(*) FROM ao;
  1: COMMIT;
  3: INSERT INTO ao VALUES (0);
  