MySQL Innodb如何找出阻塞事务源头SQL

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mysql数据库中出现了阻塞问题,如何快速查找定位问题根源?在实验开始前,我们先梳理一下有什么工具或命令查看MySQL的阻塞,另外,我们也要一一对比其优劣,因为有些命令可能在实际环境下可能并不适用。

 

1:  show engine innodb status

 

2:  Innotop工具

 

3:  INNODB_TRX 等系统表

 

 

 

下面我们理论联系实际,通过实验来测试总结一下这个问题。首先构造测试环境,数据库测试环境为( 5.7.21 MySQL Community Server 和5.6.20-enterprise-commercial,这两个测试环境我都测试验证过)

 

mysql> use MyDB;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
 
Database changed
mysql> create table test_blocking(id int primary key, name varchar(12));
Query OK, 0 rows affected (0.05 sec)
 
mysql> insert into test_blocking
    -> select 1, \'kerry\' from dual;
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0
 
mysql> insert into test_blocking
    -> select 2, \'jimmy\' from dual;
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0
 
mysql> insert into test_blocking
    -> select 3, \'kkk\' from dual;
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

 

 

准备好测试环境数据后,那么我们接下来开始实验,为了实验效果,我们先将参数innodb_lock_wait_timeout设置为100。

 

 

mysql> show variables like \'innodb_lock_wait_timeout\';
+--------------------------+-------+
| Variable_name            | Value |
+--------------------------+-------+
| innodb_lock_wait_timeout | 50    |
+--------------------------+-------+
1 row in set (0.00 sec)
 
mysql> set global innodb_lock_wait_timeout=100 ;
Query OK, 0 rows affected (0.00 sec)
 
 
mysql> select connection_id() from dual;
+-----------------+
| connection_id() |
+-----------------+
|               8 |
+-----------------+
1 row in set (0.00 sec)
 
mysql> set session autocommit=0;
Query OK, 0 rows affected (0.00 sec)
 
mysql> select * from test_blocking where id=1 for update;
+----+-------+
| id | name  |
+----+-------+
|  1 | kerry |
+----+-------+
1 row in set (0.00 sec)

 

 

然后在第二个连接会话中执行更新脚本,构造被阻塞的案例

 

 

mysql> select connection_id() from dual;
+-----------------+
| connection_id() |
+-----------------+
|               9 |
+-----------------+
1 row in set (0.00 sec)
 
mysql> update test_blocking set name=\'kk\' where id=1;

 

 

在第三个连接会话执行下面命令,查看TRANSACTIONS相关信息:

 

 

mysql> show engine innodb status\\G;

 

 

clip_image001

 

使用show engine innodb status命令后,可以查看其输出的TRANSACTIONS部分信息,如上截图所示,找到类似TRX HAS BEEN WATING ...部分的信息,

通过那部分信息,我们可以看到update test_blocking set name=\'kk\' where id=1这个SQL语句被阻塞了14秒,一直在等待获取X Lock。

 

 

TRANSACTIONS

------------

Trx id counter 148281  #下一个事务ID

Purge done for trx\'s n:o < 148273 undo n:o < 0 state: running but idle

History list length 552

LIST OF TRANSACTIONS FOR EACH SESSION:

---TRANSACTION 0, not started

MySQL thread id 15, OS thread handle 0x4cc64940, query id 261 localhost root cleaning up

---TRANSACTION 0, not started

MySQL thread id 14, OS thread handle 0x4cbe2940, query id 278 localhost root init

show engine innodb status

---TRANSACTION 148280, ACTIVE 24 sec

2 lock struct(s), heap size 360, 1 row lock(s)

MySQL thread id 8, OS thread handle 0x4cba1940, query id 276 localhost root cleaning up

---TRANSACTION 148279, ACTIVE 313 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 9, OS thread handle 0x4cc23940, query id 277 localhost root updating  #线程ID为9, 操作系统线程句柄为0x4cc23940, 查询ID为277,账号为root的UPDATE操作

update test_blocking set name=\'kk\' where id=1  #具体SQL语句

------- TRX HAS BEEN WAITING 14 SEC FOR THIS LOCK TO BE GRANTED:  #TRX等待授予锁已经有14秒了

RECORD LOCKS space id 337 page no 3 n bits 72 index `PRIMARY` of table `MyDB`.`test_blocking` trx id 148279 lock_mode X locks rec but not gap waiting

#在space id=337(test_blocking表的表空间),page no=3的页上,表test_blocking上的主键索引在等待X锁

Record lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 0

 0: len 4; hex 80000001; asc     ;;            #第一个字段是主键,制度按长为4,值为1

 1: len 6; hex 000000024322; asc     C";;      #该字段为6个字节的事务id,这个id表示最近一次被更新的事务id(对应十进制为148258)

 2: len 7; hex 9a000001f20110; asc        ;;   #该字段为7个字节的回滚指针,用于mvcc

 3: len 5; hex 6b65727279; asc kerry;;         #该字段表示的是此记录的第二个字段,长度为5,值为kerry(如果表有多个字段,那么此处后面还有记录)

 

clip_image002

 

mysql> select * from information_schema.INNODB_SYS_DATAFILES where space=337;
+-------+--------------------------+
| SPACE | PATH                     |
+-------+--------------------------+
|   337 | ./MyDB/test_blocking.ibd |
+-------+--------------------------+
1 row in set (0.00 sec)
 
mysql> 

 

 

clip_image003

 

 

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