小编raf*_*fbm的帖子

我在摆弄VACUUM并注意到一些意想不到的行为，其中SELECT从表中ing 行似乎减少了VACUUM之后必须做的工作。

测试数据

注意：autovacuum 被禁用

CREATE TABLE numbers (num bigint);
ALTER TABLE numbers SET (
  autovacuum_enabled = 'f',
  toast.autovacuum_enabled = 'f'
);

INSERT INTO numbers SELECT generate_series(1, 5000);

试验 1

现在我们对所有行运行更新，

UPDATE numbers SET num = 0;

当我们跑步时，VACUUM (VERBOSE) numbers;我们得到，

INFO:  vacuuming "public.numbers"
INFO:  "numbers": removed 5000 row versions in 23 pages
INFO:  "numbers": found 5000 removable, 5000 nonremovable row versions in 45 out of 45 pages
DETAIL:  0 dead row versions …