选择更新甚至排序之间的PostgreSQL死锁

Question

我有两个死锁在一起的查询

PERFORM id
FROM stack
WHERE id IN (SELECT tmp.stkid FROM tmp_push_bulk tmp WHERE tmp.stkid > 0)
ORDER BY id
FOR UPDATE OF stack

和

PERFORM stk.id
FROM stack stk
WHERE stk.referer IN (
      SELECT tmp.id
      FROM tmp_renew_stk tmp
)
ORDER BY stk.id
FOR UPDATE OF stk

错误是：

- PG (20:46:37) [14786]: Execute command failed: ERROR:  deadlock detected
DETAIL:  Process 14797 waits for ShareLock on transaction 183495696; blocked by process 24303.
Process 24303 waits for ShareLock on transaction 183495704; blocked by process 14797.
HINT:  See server log for query details.

我也认为每个进程都按照 id 列的顺序锁定它的行，所以死锁是不可能的。谁能告诉我为什么？

Answer 1

可能是IN 表达式以非特定顺序锁定行（未经测试）。我通常会在可能的情况下用JOIN 替换更大的集合上的IN。这开始时速度更快，从而最大限度地减少了死锁的机会。我会尝试：

更新：根据您的评论，您有很多重复项。假设临时表中存在欺骗，我建议出于三个目的使用子查询：

• 折叠副本。
• 使用DISTINCT 在子查询中同时对行进行排序特别便宜。
• 申请WHERE条件AND tmp.stkid > 0

PERFORM s.id
FROM  stack s
JOIN  (
   SELECT DISTINCT stkid
   FROM   tmp_push_bulk
   WHERE  stkid > 0
   ) tmp ON tmp.stkid = s.id 
ORDER BY 1
FOR   UPDATE OF s;

还有：

PERFORM s.id
FROM  stack s
JOIN  (
   SELECT DISTINCT id
   FROM   tmp_renew_stk
   ) tmp ON tmp.id = s.referer
ORDER BY 1
FOR   UPDATE OF s;