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日常开发中，经常遇到事务未提交或者阻塞导致数据库死锁，下面看看如何查找具体死锁原因
问题
WARN - SQL Error: 1213, SQLState: 40001
ERROR - Deadlock found when trying to get lock; try restarting transaction
1. 查看锁阻塞线程信息
这里用几中方法进行分析：1.1 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)
如果数据库存在较多线程的话，这种方法确实不太好确认的。
1.2 直接使用show engine innodb status查看
- ------------
- TRANSACTIONS
- ------------
- Trx id counter 4131
- Purge done for trx's n:o < 4119 undo n:o < 0 state: running but idle
- History list length 126
- LIST OF TRANSACTIONS FOR EACH SESSION:
- ---TRANSACTION 0, not started
- MySQL thread id 2, OS thread handle 0x7f953ffff700, query id 115 localhost root init
- show engine innodb status
- ---TRANSACTION 4130, ACTIVE 41 sec starting index read
- mysql tables in use 1, locked 1
- LOCK 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 updating
- delete from emp where empno=7788
- ------- TRX HAS BEEN WAITING 41 SEC FOR THIS LOCK TO BE GRANTED: ## 等待了41s
- RECORD 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 waiting
- Record 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 read
- mysql tables in use 1, locked 1
- LOCK 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 updating
- update emp set sal=3500 where empno=7788
- ------- TRX HAS BEEN WAITING 45 SEC FOR THIS LOCK TO BE GRANTED: ## 等待了45s
- RECORD 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 waiting
- Record 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 sec
- 2 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
我们知道，主要根因还是thread=3引起的，但从innodb status中却无法分析得到这个结果。
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。
1.3 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 lock
- 7 test.emp Locked - write High priority write lock
这种方法中，能找到线程ID=3和7是阻塞者，但还是不太准确，判断不出来线程7也是被线程ID=3阻塞的。
1.4 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 monitor
- Query OK, 0 rows affected, 1 warning (0.07 sec)
- MySQL [test]> show warnings\G
- *************************** 1. row ***************************
- Level: Warning
- Code: 131
- Message: 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)
说明：这个在5.6中有一个warning，但不影响使用。
然后再使用show engine innodb status查看：
- ------------
- TRANSACTIONS
- ------------
- Trx id counter 4667
- Purge done for trx's n:o < 4659 undo n:o < 0 state: running but idle
- History list length 138
- LIST OF TRANSACTIONS FOR EACH SESSION:
- ---TRANSACTION 0, not started
- MySQL thread id 9, OS thread handle 0x7f813c5f7700, query id 152 localhost root init
- show engine innodb status
- ---TRANSACTION 4663, ACTIVE 78 sec starting index read
- mysql tables in use 1, locked 1
- LOCK 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 updating
- delete from emp where empno=7788
- ------- TRX HAS BEEN WAITING 78 SEC FOR THIS LOCK TO BE GRANTED: ## 等待了78s
- RECORD 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 waiting
- Record 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IX
- RECORD 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 waiting
- Record 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 read
- mysql tables in use 1, locked 1
- LOCK 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 updating
- update emp set sal=3500 where empno=7788
- ------- TRX HAS BEEN WAITING 81 SEC FOR THIS LOCK TO BE GRANTED: ## 等待了81s
- RECORD 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 waiting
- Record 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IX
- RECORD 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 waiting
- Record 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 1222
- mysql tables in use 2, locked 0
- 2 lock struct(s), heap size 360, 1 row lock(s)
- MySQL thread id 3, OS thread handle 0x7f813c659700, query id 147 localhost root Sending data
- select count(*) from t3 a,t3 b ## 这是线程3当前正在执行的SQL
- Trx read view will not see trx with id >= 4662, sees < 4659
- TABLE 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=3
- RECORD 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 gap
- Record 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 ;;
为什么线程3当前执行的是一个select t3表操作，但却锁住了test.emp表上page num=3？
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。
2 结论
在分析innodb中锁阻塞时，几种方法的对比情况：
（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。