指定VACUUM在扫描表时用来决定是否冻结行版本的切断年龄(以事务计)。默认值是 5 千万个事务。尽管用户可以将这个值设置为从 0 到 10 亿,VACUUM会悄悄地将有效值设置为autovacuum_freeze_max_age值的一半,这样在强制执行的自动清理之间不会有过短的时间间隔。更多信息请见vacuum-for-wraparound

建议 [EN]

Most users will want to decrease this so that rows which have been cold for a long time get frozen earlier, and avoid an autovacuum_freeze. The suggestion of 500000 is for a moderately busy database; do not set to less than a few hours worth of XIDs. Maximum setting is 1/2 of autovaccuum_max_freeze_age.