作者

digoal

日期

2020-11-10

标签

PostgreSQL , pg_lwlock_blocking_pid , lwlock 堵塞诊断

背景

当前lw lock这种轻量锁的等待没有跟踪数据, 所以无法知道谁堵塞了谁, 只知道在等待lw事件.

PG 14可能引入支持lw lock的等待跟踪, 需要改lw锁结构, 锁的存储可能变得更重, 具体实现PG社区还在讨论中.

https://www.postgresql.org/message-id/flat/71779d05-3a9b-b897-f54d-16ffedcc896b@amazon.com

https://commitfest.postgresql.org/30/2576/

```

select query,pid,state,wait_event,wait_event_type,pg_lwlock_blocking_pid(pid),pg_blocking_pids(pid) from pg_stat_activity where state='active' and pid != pg_backend_pid();

          query              |  pid  | state  |  wait_event   | wait_event_type |          pg_lwlock_blocking_pid           | pg_blocking_pids

--------------------------------+-------+--------+---------------+-----------------+-------------------------------------------+------------------

insert into bdtlwa values (1); | 10232 | active | | | (,,,) | {}

insert into bdtlwb values (1); | 10254 | active | WALInsert | LWLock | (LW_WAIT_UNTIL_FREE,10232,LW_EXCLUSIVE,1) | {}

create table bdtwt (a int); | 10256 | active | WALInsert | LWLock | (LW_WAIT_UNTIL_FREE,10232,LW_EXCLUSIVE,1) | {}

insert into bdtlwa values (2); | 10259 | active | BufferContent | LWLock | (LW_EXCLUSIVE,10232,LW_EXCLUSIVE,1) | {}

drop table bdtlwd; | 10261 | active | WALInsert | LWLock | (LW_WAIT_UNTIL_FREE,10232,LW_EXCLUSIVE,1) | {}

(5 rows)

So, should a PID being blocked on a LWLock we could see:

• in which mode request it is waiting
• the last pid holding the lock
• the mode of the last PID holding the lock
• the number of PID(s) holding the lock
  ```

PostgreSQL 许愿链接

您的愿望将传达给PG kernel hacker、数据库厂商等, 帮助提高数据库产品质量和功能, 说不定下一个PG版本就有您提出的功能点. 针对非常好的提议，奖励限量版PG文化衫、纪念品、贴纸、PG热门书籍等，奖品丰富，快来许愿。开不开森.

9.9元购买3个月阿里云RDS PostgreSQL实例

PostgreSQL 解决方案集合

德哥 / digoal's github - 公益是一辈子的事.