Postgresql中的咨询锁超时 [英] Timeout on advisory locks in postgresql
问题描述
我正在从ORACLE迁移.目前,我正在尝试移植此呼叫:
I'm migrating from ORACLE. Currently I'm trying to port this call:
lkstat := DBMS_LOCK.REQUEST(lkhndl, DBMS_LOCK.X_MODE, lktimeout, true);
此函数尝试获取锁lkhndl
,如果在timeout
秒后未能获取它,则返回1.
This function tries to acquire lock lkhndl
and returns 1 if it fails to get it after timeout
seconds.
在Postgresql中,我使用
In postgresql I use
pg_advisory_xact_lock(lkhndl);
但是,似乎它会永远等待锁定. pg_try_advisory_xact_lock
如果失败则立即返回.有没有一种方法可以实现锁获取的超时版本?
However, it seems that it waits for lock forever. pg_try_advisory_xact_lock
returns immediately if fails. Is there a way to implement timeout version of lock acquiring?
有 lock_timeout
设置,但我不确定它是否适用于
There is lock_timeout
setting, but I'm not sure is it applicable to advisory locks and how pg_advisory_xact_lock
would behave after timeout.
推荐答案
这是包装器的原型,该包装器无法很好地模拟DBMS_LOCK.REQUEST
-仅限于一种类型的锁(事务范围咨询锁).
This is a prototype of a wrapper that poorly emulates DBMS_LOCK.REQUEST
- constrained to only one type of lock (transaction-scope advisory lock).
要使功能与Oracle完全兼容,它需要数百行.但这是一个开始.
To make function fully compatible with Oracle's, it would need several hundreds lines. But that's a start.
CREATE OR REPLACE FUNCTION
advisory_xact_lock_request(p_key bigint, p_timeout numeric)
RETURNS integer
LANGUAGE plpgsql AS $$
/* Imitate DBMS_LOCK.REQUEST for PostgreSQL advisory lock.
Return 0 on Success, 1 on Timeout, 3 on Parameter Error. */
DECLARE
t0 timestamptz := clock_timestamp();
BEGIN
IF p_timeout NOT BETWEEN 0 AND 86400 THEN
RAISE WARNING 'Invalid timeout parameter';
RETURN 3;
END IF;
LOOP
IF pg_try_advisory_xact_lock(key) THEN
RETURN 0;
ELSIF clock_timestamp() > t0 + (p_timeout||' seconds')::interval THEN
RAISE WARNING 'Could not acquire lock in % seconds', p_timeout;
RETURN 1;
ELSE
PERFORM pg_sleep(0.01); /* 10 ms */
END IF;
END LOOP;
END;
$$;
使用以下代码对其进行测试:
Test it using this code:
SELECT CASE
WHEN advisory_xact_lock_request(1, 2.5) = 0
THEN pg_sleep(120)
END; -- and repeat this in parallel session
/* Usage in Pl/PgSQL */
lkstat := advisory_xact_lock_request(lkhndl, lktimeout);
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