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MySQL鎖阻塞的深入分析

日常維護(hù)中，經(jīng)常會(huì)碰到線程被阻塞，導(dǎo)致數(shù)據(jù)庫響應(yīng)非常慢，下面就看看如何獲取是哪個(gè)線程導(dǎo)致了阻塞的。

1. 環(huán)境說明

RHEL 6.4 x86_64 + MySQL 5.6.19

事務(wù)隔離級(jí)別：RR

2. 測(cè)試過程

3. 查看鎖阻塞線程信息

這里用幾中方法進(jìn)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)

如果數(shù)據(jù)庫存在較多線程的話，這種方法確實(shí)不太好確認(rèn)的。

3.2 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 ## 線程4在等待往test.emp中的主鍵上加X鎖，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 ## 線程7在等待往test.emp中的主鍵上加X鎖，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

我們知道，主要根因還是thread=3引起的，但從innodb status中卻無法分析得到這個(gè)結(jié)果。

從上面來看，線程4和線程7都在等待往test.emp中的主鍵上加X鎖，page num=3，但是線程7等待的時(shí)間為45s，而線程4等待的時(shí)間為41s，是較線程7之后申請(qǐng)的鎖，所以可以判斷是線程7阻塞了線程4。至于線程7為什么出現(xiàn)等待，這里分析不到根因。

3.3 使用mysqladmin debug查看

# mysqladmin -S /tmp/mysql3306.sock debug

然后在error日志中，會(huì)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

這種方法中，能找到線程ID=3和7是阻塞者，但還是不太準(zhǔn)確，判斷不出來線程7也是被線程ID=3阻塞的。

3.4 使用innodb_lock_monitor來獲取阻塞鎖線程

MySQL [test]> CREATE TABLE innodb_lock_monitor (a INT) ENGINE=INNODB; ## 隨便在一個(gè)數(shù)據(jù)庫中創(chuàng)建這個(gè)表，就會(huì)打開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)

說明：這個(gè)在5.6中有一個(gè)warning，但不影響使用。

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 ## 線程4在等待往test.emp中的主鍵上加X鎖，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  ## 在給主鍵行上加X鎖之前，先要在表上加意向鎖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 ## 線程7在等待往test.emp中的主鍵上加X鎖，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  ## 在給主鍵行上加X鎖之前，先要在表上加意向鎖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  ## 這是線程3當(dāng)前正在執(zhí)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 ## 線程3中正在擁有表上的意向IX鎖，并且有test.emp表上主鍵的行級(jí)X鎖，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   ;;

為什么線程3當(dāng)前執(zhí)行的是一個(gè)select t3表操作，但卻鎖住了test.emp表上page num=3？

有可能是線程3之前對(duì)test.emp表的操作事務(wù)沒有及時(shí)提交導(dǎo)致。

所以得出：線程3阻塞了線程7，而線程7又阻塞了線程4，所以根因就是線程3，讓線程3盡快提交或是kill掉即可。

4. 結(jié)論

在分析innodb中鎖阻塞時(shí)，幾種方法的對(duì)比情況：

（1）使用show processlist查看不靠譜；

（2）直接使用show engine innodb status查看，無法判斷到問題的根因；

（3）使用mysqladmin debug查看，能看到所有產(chǎn)生鎖的線程，但無法判斷哪個(gè)才是根因；

（4）開啟innodb_lock_monitor后，再使用show engine innodb status查看，能夠找到鎖阻塞的根因。

原文鏈接：https://blog.csdn.net/hw_libo/article/details/39080809

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