postgresql - Postgresql 9.5 alter table 在没有其他长时间运行的查询的情况下获得锁定超时
问题描述
我试图执行alter table mydb.r_group drop constraint test;
但是获得排他锁需要超过 2 分钟。该表是繁忙的表,有许多进程对其进行查询。(进程使用 jdbc 访问数据库)
idle
我试图使用以下查询语句找到一个长时间运行的查询,但除了一些带有状态的查询之外找不到任何查询。
SELECT
pid,
now() - pg_stat_activity.query_start AS duration,
query,
state
FROM pg_stat_activity
WHERE (now() - pg_stat_activity.query_start) > interval '5 minutes';
我还尝试使用以下查询语句查找阻止更改表查询的查询,但该查询也被阻止,因此无法获取数据。
SELECT blocked_locks.pid AS blocked_pid,
blocked_activity.usename AS blocked_user,
blocking_locks.pid AS blocking_pid,
blocking_activity.usename AS blocking_user,
blocked_activity.query AS blocked_statement,
blocking_activity.query AS current_statement_in_blocking_process
FROM pg_catalog.pg_locks blocked_locks
JOIN pg_catalog.pg_stat_activity blocked_activity ON blocked_activity.pid = blocked_locks.pid
JOIN pg_catalog.pg_locks blocking_locks
ON blocking_locks.locktype = blocked_locks.locktype
AND blocking_locks.DATABASE IS NOT DISTINCT FROM blocked_locks.DATABASE
AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation
AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page
AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple
AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid
AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid
AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid
AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid
AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid
AND blocking_locks.pid != blocked_locks.pid
JOIN pg_catalog.pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid
WHERE NOT blocked_locks.GRANTED;
有谁知道我可以采取哪些其他步骤来找到根本原因?
解决方案
首先,尝试找到有问题的表的对象 ID:
SELECT tableoid
FROM mydb.r_group
LIMIT 1;
然后找到这张表上的所有锁:
SELECT pid, mode, granted
FROM pg_locks
WHERE database = current_database()
AND locktype = 'relation'
AND relation = <the number from above>;
然后你有一个所有会阻止ALTER TABLE
.
寻找这些pid
spg_stat_activity
看看他们在做什么。特别有趣的是xact_start
,活动事务开始的时间。
如果在 中找不到阻塞进程pg_stat_activity
,它也可能是一个后台进程,很可能是一个反环绕 autovacuum 工作者。查找ps
在 shell 上使用的阻塞进程 ID。
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