heap_force_kill 在不检查元组的情况下，将“used”行指针标记为“dead”。该函数的预期用途是强制移除那些无法通过其他方式访问的元组。例如：

test=> select * from t1 where ctid = '(0, 1)';
ERROR:  could not access status of transaction 4007513275
DETAIL:  Could not open file "pg_xact/0EED": No such file or directory.

test=# select heap_force_kill('t1'::regclass, ARRAY['(0, 1)']::tid[]);
 heap_force_kill
-----------------

(1 row)

test=# select * from t1 where ctid = '(0, 1)';
(0 rows)

heap_force_freeze 在不检查元组数据的情况下，将元组标记为已冻结。该函数的预期用途是使那些因可见性信息损坏而无法访问的元组重新变为可访问，或者解决因可见性信息损坏而导致无法成功对表执行清理（VACUUM）的问题。例如：

test=> vacuum t1;
ERROR:  found xmin 507 from before relfrozenxid 515
CONTEXT:  while scanning block 0 of relation "public.t1"

test=# select ctid from t1 where xmin = 507;
 ctid
-------
 (0,3)
(1 row)

test=# select heap_force_freeze('t1'::regclass, ARRAY['(0, 3)']::tid[]);
 heap_force_freeze
-------------------

(1 row)

test=# select ctid from t1 where xmin = 2;
 ctid
-------
 (0,3)
(1 row)