Postgresql 9.5 alter table 在没有其他长运行查询的情况下获得锁定超时

Question

我正在尝试执行 alter table mydb.r_group drop constraint test; 但是它花了 2 分钟多才获得独占锁。 table 正忙 table 有许多进程在查询它。（进程使用 jdbc 访问数据库）

我试图使用以下查询语句找到一个长运行查询，但除了一些具有 idle 状态的查询外找不到任何其他查询。

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找到阻止更改 table 查询的查询，但此查询也被阻止，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？

Answer 1

首先，尝试找到有问题的 table 的对象 ID：

SELECT tableoid
FROM mydb.r_group
LIMIT 1;

然后找到这个table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 的会话的列表。

在 pg_stat_activity 中寻找这些 pid，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。

如果您在 pg_stat_activity 中找不到阻塞进程，它也可能是后台进程，很可能是 anti-wraparound autovacuum worker。在 shell.

上使用 ps 查找阻塞进程 ID

Postgresql 9.5 alter table 在没有其他长运行查询的情况下获得锁定超时

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Postgresql 9.5 alter table 在没有其他长运行查询的情况下获得锁定超时