tzwweixiao 2019-11-21
很多时候我们在MySQL数据库中会经常出现事务之间阻塞的问题,也就是阻塞lock,oracle的话实际上之前提供的脚本已经可以很直观看出阻塞的问题,那么对于mysql数据库我们应如何快速查找定位问题根源?
之前分享了innotop工具和show engine innodb status都不能很好的解决我们的需求,所以今天主要基于几张事务表来写sql看能不能定位到。
数据库:mysql5.7.24 操作系统:centos7.3
1、数据准备
create database t DEFAULT CHARSET utf8 COLLATE utf8_general_ci; use t; create table test_blocking(id int primary key, name varchar(12)); insert into test_blocking select 1, 'hwb' from dual; insert into test_blocking select 2, 'hwb2' from dual; insert into test_blocking select 3, 'hwb3' from dual;
2、参数设置
为了实验效果,我们先将参数innodb_lock_wait_timeout设置为100,否则很快就会提示ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
show variables like 'innodb_lock_wait_timeout'; set global innodb_lock_wait_timeout=100 ;
1、第一个会话
select connection_id() from dual; set session autocommit=0; select * from test_blocking where id=1 for update;
2、第二个会话
在第二个连接会话中执行更新脚本
select connection_id() from dual; update test_blocking set name='kk' where id=1;
3、第三个会话--通过查询information_schema数据库下与事务相关的几个系统表
--查看哪个线程被哪个堵塞,waiting_thread_id代表等待线程,blocking_thread_id代表堵塞线程 SELECT r.trx_id waiting_trx_id, r.trx_mysql_thread_id waiting_thread_id, r.trx_query waiting_query, b.trx_id blocking_trx_id, b.trx_mysql_thread_id blocking_thread_id, b.trx_query blocking_query, now( ) - r.TRX_STARTED blocking_time FROM information_schema.innodb_lock_waits w INNER JOIN information_schema.innodb_trx b ON b.trx_id = w.blocking_trx_id INNER JOIN information_schema.innodb_trx r ON r.trx_id = w.requesting_trx_id; --查看源头sql SELECT a.sql_text, c.id, d.trx_started, b.processlist_user, b.processlist_host FROM PERFORMANCE_SCHEMA.events_statements_current a JOIN PERFORMANCE_SCHEMA.threads b ON a.thread_id = b.thread_id JOIN information_schema.PROCESSLIST c ON b.processlist_id = c.id JOIN information_schema.innodb_trx d ON c.id = d.trx_mysql_thread_id WHERE c.id = 304192 ORDER BY d.trx_started;
如下截图所示,第一个SQL语句能够查到线程304193被线程304192阻塞了, 被阻塞的SQL语句为“update test_blocking set name='kk' where id=1;”, 能够查到被阻塞了多长时间,但是无法查到源头SQL语句。此时就需要第二个SQL语句登场,找到源头语句。
ps:附一段查看阻塞线程更多信息的sql
SELECT p2.HOST Blockedhost, p2.USER BlockedUser, r.trx_id BlockedTrxId, r.trx_mysql_thread_id BlockedThreadId, TIMESTAMPDIFF( SECOND, r.trx_wait_started, CURRENT_TIMESTAMP ) WaitTime, r.trx_query BlockedQuery, l.lock_table BlockedTable, m.lock_mode BlockedLockMode, m.lock_type BlockedLockType, m.lock_index BlockedLockIndex, m.lock_space BlockedLockSpace, m.lock_page BlockedLockPage, m.lock_rec BlockedLockRec, m.lock_data BlockedLockData, p.HOST blocking_host, p.USER blocking_user, b.trx_id BlockingTrxid, b.trx_mysql_thread_id BlockingThreadId, b.trx_query BlockingQuery, l.lock_mode BlockingLockMode, l.lock_type BlockingLockType, l.lock_index BlockingLockIndex, l.lock_space BlockingLockSpace, l.lock_page BlockingLockPage, l.lock_rec BlockingLockRec, l.lock_data BlockingLockData, IF ( p.COMMAND = 'Sleep', CONCAT( p.TIME, ' seconds' ), 0 ) idel_in_trx FROM information_schema.INNODB_LOCK_WAITS w INNER JOIN information_schema.INNODB_TRX b ON b.trx_id = w.blocking_trx_id INNER JOIN information_schema.INNODB_TRX r ON r.trx_id = w.requesting_trx_id INNER JOIN information_schema.INNODB_LOCKS l ON w.blocking_lock_id = l.lock_id AND l.lock_trx_id = b.trx_id INNER JOIN information_schema.INNODB_LOCKS m ON m.lock_id = w.requested_lock_id AND m.lock_trx_id = r.trx_id INNER JOIN information_schema.PROCESSLIST p ON p.ID = b.trx_mysql_thread_id INNER JOIN information_schema.PROCESSLIST p2 ON p2.ID = r.trx_mysql_thread_id ORDER BY WaitTime DESC \G;
这里不要太天真的认为第二个SQL语句能够获取所有场景下的阻塞源头SQL语句,实际业务场景,会话可能在执行一个存储过程或复杂的业务,有可能它执行完阻塞源头SQL后,继续在执行其它SQL语句,此时,你抓取的是这个连接会话最后执行的SQL语句。觉得有用的朋友多帮忙转发哦!后面会分享更多devops和DBA方面的内容,感兴趣的朋友可以关注下~