PostgreSQL PARSE等待一例
发布时间：2020-12-13 17:44:59 所属栏目：百科 来源：网络整理
导读：某系统发送异常，经查有大量waiting. skyurs=# select procpid,query_start,waiting,current_query from pg_stat_activity; procpid | query_start | waiting | current_qu ery ---------+-------------------------------+---------+----------------------
|
某系统发送异常，经查有大量waiting.
skyurs=# select procpid,query_start,waiting,current_query from pg_stat_activity;
procpid | query_start | waiting | current_qu
ery
---------+-------------------------------+---------+--------------------------------------------------------------------------------
--------------------------------------------------------------------------
22048 | 2010-08-27 14:30:24.673425+08 | f | create table urs_test_user_list as select user_id,count(user_id) from urs_user_
relation a where relation=1 group by user_id having(count(user_id)>50) r+
| | | and (select count(*) from urs_user_relation where relation=1 and buddy_id=a.use
r_id limit 50)=50r +
| | | limit 400000r
+
| | |
2634 | 2010-08-27 19:27:06.622968+08 | t | select buddy_id,group_id,relation,appinfo,extinfo,create_time from skyurs
.urs_user_relation where user_id=$1 and relation=1
12932 | 2010-08-27 20:05:50.278318+08 | t | select buddy_id,create_time from skyurs
.urs_user_relation where user_id=$1 and relation=1
建表语句:create table urs_test_user_list as select user_id,count(user_id) from urs_user_
relation a where relation=1 group by user_id having(count(user_id)>50) r+
| | | and (select count(*) from urs_user_relation where relation=1 and buddy_id=a.use
r_id limit 50)=50r +
| | | limit 400000
把表 urs_user_relation给锁了，导致相关的SELECT都处于等待锁状态.
skyurs=# select pg_terminate_backend(22048);
pg_terminate_backend
----------------------
t
(1 row)
干掉之后，锁消失。
结束后查看数据库日志：
出现大量:
2010-08-28 10:56:53.735 CST,"skyurs",17107,"192.168.171.39:40721",4c77adcc.42d3,3,"PARSE",2010-08-27 20:21:32 CST,74/157,
LOG,00000,"duration: 52520677.542 ms parse <unnamed>: select buddy_id,create_time from skyu
rs.urs_user_relation where user_id=$1 and relation=1",""
总结：
1. 生产环境跑长SQL必须引起注意.这种SQL必须人在现场看牢。以及时响应。
2. 这个建表语句可以改一下，先把表建好，再用insert into select语法写入，这样的话锁没这么大。
当然，PostgreSQL应该降低这类情形下的锁级别才对。
3. 可以考虑配置超时机制，超时的SQL返回错误，以免锁过长时间才发现
4. 监控超时SQL，及时反馈给DBA处理。
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