MySQL锁阻塞的深入分析

日常维护中，经常会碰到线程被阻塞，导致数据库响应非常慢，下面就看看如何获取是哪个线程导致了阻塞的。

1. 环境说明

RHEL 6.4 x86_64 + MySQL 5.6.19

事务隔离级别：RR

2. 测试过程

3. 查看锁阻塞线程信息

这里用几中方法进行分析：

3.1 使用show processlist查看

MySQL [(none)]> show processlist;+----+------+-----------+------+---------+------+--------------+------------------------------------------+| Id | User | Host  | db | Command | Time | State  | Info          |+----+------+-----------+------+---------+------+--------------+------------------------------------------+| 2 | root | localhost | NULL | Query | 0 | init   | show processlist       || 3 | root | localhost | test | Query | 70 | Sending data | select count(*) from t3 a,t3 b   || 4 | root | localhost | test | Query | 65 | updating  | delete from emp where empno=7788   || 7 | root | localhost | test | Query | 68 | updating  | update emp set sal=3500 where empno=7788 |+----+------+-----------+------+---------+------+--------------+------------------------------------------+4 rows in set (0.00 sec)

3.2 直接使用show engine innodb status查看

------------TRANSACTIONS------------Trx id counter 4131Purge done for trx's n:o < 4119 undo n:o < 0 state: running but idleHistory list length 126LIST OF TRANSACTIONS FOR EACH SESSION:---TRANSACTION 0, not startedMySQL thread id 2, OS thread handle 0x7f953ffff700, query id 115 localhost root initshow engine innodb status---TRANSACTION 4130, ACTIVE 41 sec starting index readmysql tables in use 1, locked 1LOCK WAIT 2 lock struct(s), heap size 360, 1 row lock(s)MySQL thread id 4, OS thread handle 0x7f953ff9d700, query id 112 localhost root updatingdelete from emp where empno=7788------- TRX HAS BEEN WAITING 41 SEC FOR THIS LOCK TO BE GRANTED: ## 等待了41sRECORD LOCKS space id 16 page no 3 n bits 88 index `PRIMARY` of table `test`.`emp` trx id 4130 lock_mode X locks rec but not gap waitingRecord lock, heap no 9 PHYSICAL RECORD: n_fields 10; compact format; info bits 0 ## 线程4在等待往test.emp中的主键上加X锁，page num=3 0: len 4; hex 80001e6c; asc l;; 1: len 6; hex 000000001018; asc  ;; 2: len 7; hex 91000001420084; asc  B ;; 3: len 5; hex 53434f5454; asc SCOTT;; 4: len 7; hex 414e414c595354; asc ANALYST;; 5: len 4; hex 80001d8e; asc  ;; 6: len 4; hex 208794f0; asc  ;; 7: len 4; hex 80000bb8; asc  ;; 8: SQL NULL; 9: len 4; hex 80000014; asc  ;; ---------------------TRANSACTION 4129, ACTIVE 45 sec starting index readmysql tables in use 1, locked 1LOCK WAIT 2 lock struct(s), heap size 360, 1 row lock(s)MySQL thread id 7, OS thread handle 0x7f953ff6c700, query id 111 localhost root updatingupdate emp set sal=3500 where empno=7788------- TRX HAS BEEN WAITING 45 SEC FOR THIS LOCK TO BE GRANTED: ## 等待了45sRECORD LOCKS space id 16 page no 3 n bits 88 index `PRIMARY` of table `test`.`emp` trx id 4129 lock_mode X locks rec but not gap waitingRecord lock, heap no 9 PHYSICAL RECORD: n_fields 10; compact format; info bits 0 ## 线程7在等待往test.emp中的主键上加X锁，page num=3 0: len 4; hex 80001e6c; asc l;; 1: len 6; hex 000000001018; asc  ;; 2: len 7; hex 91000001420084; asc  B ;; 3: len 5; hex 53434f5454; asc SCOTT;; 4: len 7; hex 414e414c595354; asc ANALYST;; 5: len 4; hex 80001d8e; asc  ;; 6: len 4; hex 208794f0; asc  ;; 7: len 4; hex 80000bb8; asc  ;; 8: SQL NULL; 9: len 4; hex 80000014; asc  ;; ---------------------TRANSACTION 4128, ACTIVE 51 sec2 lock struct(s), heap size 360, 1 row lock(s)MySQL thread id 3, OS thread handle 0x7f953ffce700, query id 110 localhost root cleaning up

从上面来看，线程4和线程7都在等待往test.emp中的主键上加X锁，page num=3，但是线程7等待的时间为45s，而线程4等待的时间为41s，是较线程7之后申请的锁，所以可以判断是线程7阻塞了线程4。至于线程7为什么出现等待，这里分析不到根因。

3.3 使用mysqladmin debug查看

# mysqladmin -S /tmp/mysql3306.sock debug

然后在error日志中，会看到：

Thread database.table_name   Locked/Waiting  Lock_type  3  test.t3      Locked - read   Low priority read lock7  test.emp     Locked - write  High priority write lock

3.4 使用innodb_lock_monitor来获取阻塞锁线程

MySQL [test]> CREATE TABLE innodb_lock_monitor (a INT) ENGINE=INNODB; ## 随便在一个数据库中创建这个表，就会打开lock monitorQuery OK, 0 rows affected, 1 warning (0.07 sec) MySQL [test]> show warnings\G*************************** 1. row *************************** Level: Warning Code: 131Message: Using the table name innodb_lock_monitor to enable diagnostic output is deprecated and may be removed in future releases. Use INFORMATION_SCHEMA or PERFORMANCE_SCHEMA tables or SET GLOBAL innodb_status_output=ON.1 row in set (0.00 sec)

然后再使用show engine innodb status查看：

------------TRANSACTIONS------------Trx id counter 4667Purge done for trx's n:o < 4659 undo n:o < 0 state: running but idleHistory list length 138LIST OF TRANSACTIONS FOR EACH SESSION:---TRANSACTION 0, not startedMySQL thread id 9, OS thread handle 0x7f813c5f7700, query id 152 localhost root initshow engine innodb status---TRANSACTION 4663, ACTIVE 78 sec starting index readmysql tables in use 1, locked 1LOCK WAIT 2 lock struct(s), heap size 360, 1 row lock(s)MySQL thread id 4, OS thread handle 0x7f813c628700, query id 149 localhost root updatingdelete from emp where empno=7788------- TRX HAS BEEN WAITING 78 SEC FOR THIS LOCK TO BE GRANTED:  ## 等待了78sRECORD LOCKS space id 16 page no 3 n bits 88 index `PRIMARY` of table `test`.`emp` trx id 4663 lock_mode X locks rec but not gap waitingRecord lock, heap no 9 PHYSICAL RECORD: n_fields 10; compact format; info bits 0 ## 线程4在等待往test.emp中的主键上加X锁，page num=3 0: len 4; hex 80001e6c; asc  l;; 1: len 6; hex 000000001018; asc    ;; 2: len 7; hex 91000001420084; asc   B ;; 3: len 5; hex 53434f5454; asc SCOTT;; 4: len 7; hex 414e414c595354; asc ANALYST;; 5: len 4; hex 80001d8e; asc   ;; 6: len 4; hex 208794f0; asc   ;; 7: len 4; hex 80000bb8; asc   ;; 8: SQL NULL; 9: len 4; hex 80000014; asc   ;; ------------------TABLE LOCK table `test`.`emp` trx id 4663 lock mode IX  ## 在给主键行上加X锁之前，先要在表上加意向锁IXRECORD LOCKS space id 16 page no 3 n bits 88 index `PRIMARY` of table `test`.`emp` trx id 4663 lock_mode X locks rec but not gap waitingRecord lock, heap no 9 PHYSICAL RECORD: n_fields 10; compact format; info bits 0 0: len 4; hex 80001e6c; asc  l;; 1: len 6; hex 000000001018; asc    ;; 2: len 7; hex 91000001420084; asc   B ;; 3: len 5; hex 53434f5454; asc SCOTT;; 4: len 7; hex 414e414c595354; asc ANALYST;; 5: len 4; hex 80001d8e; asc   ;; 6: len 4; hex 208794f0; asc   ;; 7: len 4; hex 80000bb8; asc   ;; 8: SQL NULL; 9: len 4; hex 80000014; asc   ;; ---TRANSACTION 4662, ACTIVE 81 sec starting index readmysql tables in use 1, locked 1LOCK WAIT 2 lock struct(s), heap size 360, 1 row lock(s)MySQL thread id 7, OS thread handle 0x7f813c5c6700, query id 148 localhost root updatingupdate emp set sal=3500 where empno=7788------- TRX HAS BEEN WAITING 81 SEC FOR THIS LOCK TO BE GRANTED: ## 等待了81sRECORD LOCKS space id 16 page no 3 n bits 88 index `PRIMARY` of table `test`.`emp` trx id 4662 lock_mode X locks rec but not gap waitingRecord lock, heap no 9 PHYSICAL RECORD: n_fields 10; compact format; info bits 0 ## 线程7在等待往test.emp中的主键上加X锁，page num=3 0: len 4; hex 80001e6c; asc  l;; 1: len 6; hex 000000001018; asc    ;; 2: len 7; hex 91000001420084; asc   B ;; 3: len 5; hex 53434f5454; asc SCOTT;; 4: len 7; hex 414e414c595354; asc ANALYST;; 5: len 4; hex 80001d8e; asc   ;; 6: len 4; hex 208794f0; asc   ;; 7: len 4; hex 80000bb8; asc   ;; 8: SQL NULL; 9: len 4; hex 80000014; asc   ;; ------------------TABLE LOCK table `test`.`emp` trx id 4662 lock mode IX  ## 在给主键行上加X锁之前，先要在表上加意向锁IXRECORD LOCKS space id 16 page no 3 n bits 88 index `PRIMARY` of table `test`.`emp` trx id 4662 lock_mode X locks rec but not gap waitingRecord lock, heap no 9 PHYSICAL RECORD: n_fields 10; compact format; info bits 0 0: len 4; hex 80001e6c; asc  l;; 1: len 6; hex 000000001018; asc    ;; 2: len 7; hex 91000001420084; asc   B ;; 3: len 5; hex 53434f5454; asc SCOTT;; 4: len 7; hex 414e414c595354; asc ANALYST;; 5: len 4; hex 80001d8e; asc   ;; 6: len 4; hex 208794f0; asc   ;; 7: len 4; hex 80000bb8; asc   ;; 8: SQL NULL; 9: len 4; hex 80000014; asc   ;; ---TRANSACTION 4615, ACTIVE 1579 sec, thread declared inside InnoDB 1222mysql tables in use 2, locked 02 lock struct(s), heap size 360, 1 row lock(s)MySQL thread id 3, OS thread handle 0x7f813c659700, query id 147 localhost root Sending dataselect count(*) from t3 a,t3 b  ## 这是线程3当前正在执行的SQLTrx read view will not see trx with id >= 4662, sees < 4659TABLE LOCK table `test`.`emp` trx id 4615 lock mode IX ## 线程3中正在拥有表上的意向IX锁，并且有test.emp表上主键的行级X锁，page num=3RECORD LOCKS space id 16 page no 3 n bits 88 index `PRIMARY` of table `test`.`emp` trx id 4615 lock_mode X locks rec but not gapRecord lock, heap no 9 PHYSICAL RECORD: n_fields 10; compact format; info bits 0 0: len 4; hex 80001e6c; asc  l;; 1: len 6; hex 000000001018; asc    ;; 2: len 7; hex 91000001420084; asc   B ;; 3: len 5; hex 53434f5454; asc SCOTT;; 4: len 7; hex 414e414c595354; asc ANALYST;; 5: len 4; hex 80001d8e; asc   ;; 6: len 4; hex 208794f0; asc   ;; 7: len 4; hex 80000bb8; asc   ;; 8: SQL NULL; 9: len 4; hex 80000014; asc   ;;

有可能是线程3之前对test.emp表的操作事务没有及时提交导致。

所以得出：线程3阻塞了线程7，而线程7又阻塞了线程4，所以根因就是线程3，让线程3尽快提交或是kill掉即可。

4. 结论

在分析innodb中锁阻塞时，几种方法的对比情况：

（1）使用show processlist查看不靠谱；

（2）直接使用show engine innodb status查看，无法判断到问题的根因；

（3）使用mysqladmin debug查看，能看到所有产生锁的线程，但无法判断哪个才是根因；

（4）开启innodb_lock_monitor后，再使用show engine innodb status查看，能够找到锁阻塞的根因。

原文链接：https://blog.csdn.net/hw_libo/article/details/39080809