MySQL DeadLock故障排查全过程记录
发布时间：2022-03-02 15:03:56 所属栏目：MySql教程 来源：互联网
导读：【作者】 刘博：携程技术保障中心数据库高级经理，主要关注Sql server和Mysql的运维和故障处理。 【环境】 版本号：5.6.21 隔离级别：REPEATABLE READ 【问题描述】 接到监控报警，有一个线上的应用DeadLock报错，每15分钟会准时出现 登录Mysql服务器查看
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【作者】 刘博：携程技术保障中心数据库高级经理，主要关注Sql server和Mysql的运维和故障处理。 【环境】 版本号：5.6.21 隔离级别：REPEATABLE READ 【问题描述】 接到监控报警，有一个线上的应用DeadLock报错，每15分钟会准时出现 登录Mysql服务器查看日志： mysql> show engine innodb statusG *** (1) TRANSACTION: TRANSACTION 102973, ACTIVE 11 sec starting index read mysql tables in use 3, locked 3 LOCK WAIT 4 lock struct(s), heap size 1136, 3 row lock(s) MySQL thread id 6, OS thread handle 140024996574976, query id 83 localhost us updating UPDATE TestTable SET column1 = 1, Column2 = sysdate(), Column3= '026' Column4 = 0 AND column5 = 485 AND column6 = 'SEK' *** (1) WAITING FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 417 page no 1493 n bits 1000 index idx_column6 of table test.TestTable trx id 102973 lock_mode X waiting Record lock, heap no 859 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 3; hex 53454b; asc SEK;; 1: len 8; hex 80000000007e1452; asc ~ R;; *** (2) TRANSACTION: TRANSACTION 102972, ACTIVE 26 sec starting index read mysql tables in use 3, locked 3 219 lock struct(s), heap size 24784, 2906 row lock(s), undo log entries 7 MySQL thread id 5, OS thread handle 140024996841216, query id 84 localhost us updating UPDATE TestTable SET Column1 = 1, Column2 = sysdate(), Column3 = '026' Column4 = 0 AND Column5 = 485 AND Column6 = 'SEK' *** (2) HOLDS THE LOCK(S): RECORD LOCKS space id 417 page no 1493 n bits 1000 index idx_Column6 of table test.TestTable trx id 102972 lock_mode X Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0 0: len 8; hex 73757072656d756d; asc supremum;; Record lock, heap no 859 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 3; hex 53454b; asc SEK;; 1: len 8; hex 80000000007e1452; asc ~ R;; *** (2) WAITING FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 601 page no 89642 n bits 1000 index idx_column6 of table test.TestTable trx id 32231892482 lock_mode X locks rec but not gap waiting Record lock, heap no 38 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 3; hex 53454b; asc SEK;; 1: len 8; hex 80000000007eea14; asc ~ ;; 大致一看，更新同一索引的同一行，应该是一个Block，报TimeOut的错才对，怎么会报DeadLock? 【初步分析】 先分析下(2) TRANSACTION，TRANSACTION 32231892482。 等待的锁信息为： 0: len 3; hex 53454b; asc SEK;; 1: len 8; hex 80000000007eea14; asc 持有的锁信息为： 0: len 3; hex 53454b; asc SEK;; 1: len 8; hex 80000000007eeac4; asc 再先分析下(1) TRANSACTION，TRANSACTION 32231892617。 等待的锁信息为： 0: len 3; hex 53454b; asc SEK;; 1: len 8; hex 80000000007eeac4; asc 于是可以画出的死锁表，两个资源相互依赖，造成死锁： TRANSACTION Hold Wait 32231892617 53454b80000000007eea14 53454b80000000007eeac4 32231892482 53454b80000000007eeac4 53454b80000000007eea14 让我们再看一下explain结果： mysql>desc UPDATE TestTable SET Column1=1, Column2 = sysdate(),Column3 = '025' Column4 = 0 AND Column5 = 477 AND Column6 = 'SEK' G; *************************** 1. row *************************** id: 1 select_type: UPDATE table: TestTable partitions: NULL type: index_merge possible_keys: column5_index,idx_column5_column6_Column1,idxColumn6 key: column5_index,idxColumn6 key_len: 8,9 ref: NULL rows: 7 filtered: 100.00 Extra: Using intersect(column5_index,idxColumn6); Using where 可以看到 EXTRA 列： Using intersect(column5_index,idxColumn6) 从5.1开始，引入了 index merge 优化技术，对同一个表可以使用多个索引分别进行条件扫描。 相关文档：http://dev.mysql.com/doc/refman/5.7/en/index-merge-optimization.html The Index Merge method is used to retrieve rows with several range scans and to merge their results into one. The merge can produce unions, intersections, or unions-of-intersections of its underlying scans. This access method merges index scans from a single table; it does not merge scans across multiple tables. 【模拟与验证】 根据以上初步分析，猜测应该就是intersect造成的，于是在测试环境模拟验证，开启2个session模拟死锁： 时间序列 Session1 Session2 1 Begin； 2 UPDATE TestTable SET Column2 = sysdate() Column4 = 0 AND Column5 = 47 AND Column6 = 'SEK 执行成功，影响7行 3 Begin； 4 UPDATE TestTable SET Column2 = sysdate(),Column4 = 0 AND Column5 = 485 AND Column6 = 'SEK'； 被Blocking 5 UPDATE TestTable SET Column2 = sysdate(),Column4 = 0 AND Column5 = 485 AND Column6 = 'SEK'； 执行成功 ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction 依据以上信息可以发现Session2虽然被Block了，但也获取了一些Session1在时间序列5时所需资源的X锁，可以再开启一个查询select count(Column5) from TestTable where Column5 = 485，设置SET TRANSACTION ISOLATION LEVEL SERIALIZABLE，去查询Column5 = 485的行，观察锁等待的信息： mysql> SELECT r.trx_id waiting_trx_id, r.trx_mysql_thread_id waiting_thread, r.trx_query waiting_query, b.trx_id mysql> SELECT r.trx_id waiting_trx_id, r.trx_mysql_thread_id waiting_thread, r.trx_query waiting_query, b.trx_id blocking_trx_id, b.trx_mysql_thread_id blocking_thread, b.trx_query blocking_query 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 G; *************************** 1. row *************************** waiting_trx_id: 103006 waiting_thread: 36 waiting_query: UPDATE TestTable SET Column1 = 1, Column2 = sysdate(), Column3 = '026' Column4 = 0 AND Column5 = 485 AND Column6 = 'SEK' blocking_trx_id: 103003 blocking_thread: 37 blocking_query: NULL *************************** 2. row *************************** waiting_trx_id: 421500433538672 waiting_thread: 39 waiting_query: select count(Column5) from TestTable where Column5 = 485 blocking_trx_id: 103006 blocking_thread: 36 blocking_query: UPDATE TestTable SET Column1 = 1, Column2 = sysdate(), Column3 = '026' Column4 = 0 AND Column5 = 485 AND Column6 = 'SEK' 2 rows in set, 1 warning (0.00 sec) mysql> select * from information_schema.innodb_lock_waits G; *************************** 1. row *************************** requesting_trx_id: 103006 requested_lock_id: 103006:417:1493:859 blocking_trx_id: 103003 blocking_lock_id: 103003:417:1493:859 *************************** 2. row *************************** requesting_trx_id: 421500433538672 requested_lock_id: 421500433538672:417:749:2 blocking_trx_id: 103006 blocking_lock_id: 103006:417:749:2 2 rows in set, 1 warning (0.00 sec) mysql> select * from INNODB_LOCKS G; *************************** 1. row *************************** lock_id: 103006:417:1493:859 lock_trx_id: 103006 lock_mode: X lock_type: RECORD lock_table: test.TestTable lock_index: idxColumn6 lock_space: 417 lock_page: 1493 lock_rec: 859 lock_data: 'SEK', 8262738 *************************** 2. row *************************** lock_id: 103003:417:1493:859 lock_trx_id: 103003 lock_mode: X lock_type: RECORD lock_table:test.TestTable lock_index: idxColumn6 lock_space: 417 lock_page: 1493 lock_rec: 859 lock_data: 'SEK', 8262738 *************************** 3. row *************************** lock_id: 421500433538672:417:749:2 lock_trx_id: 421500433538672 lock_mode: S lock_type: RECORD lock_table: test.TestTable lock_index: column5_index lock_space: 417 lock_page: 749 lock_rec: 2 lock_data: 485, 8317620 *************************** 4. row *************************** lock_id: 103006:417:749:2 lock_trx_id: 103006 lock_mode: X lock_type: RECORD lock_table: test.TestTable lock_index: column5_index lock_space: 417 lock_page: 749 lock_rec: 2 lock_data: 485, 8317620 4 rows in set, 1 warning (0.00 sec) 可以看到Session2，trx_id 103006阻塞了trx_id 421500433538672，而trx_id 421500433538672 requested_lock也正好是lock_data: 485, 8317620。由此可见Session2虽然别block了，但是还是获取到了Index column5_index相关的锁。被Block是因为intersect的原因，还需要idxColumn6的锁，至此思路已经清晰，对整个分配锁的信息简化一下，如下表格（请求到的锁用青色表示，需获取但未获取到的锁用红色表示）： 时间点 Session1 Session2 1 477 SEK 2 485 SEK 3 485 SEK 死锁发生 可以看到485 SEK这两个资源形成了一个环状，最终发生死锁。 【解决方法】 最佳的方法是添加column5和Column6的联合索引。 我们环境当时的情况发现Column6的筛选度非常低，就删除了Column6的索引。 （编辑：应用网_镇江站长网） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |
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