MySQL提供了查看当前数据库锁请求的三种方法:
1. show full processlist命令
观察state和info列
2. show engine innodb status\G 命令
查看 TRANSACTIONS 部分和 LATEST DETECTED DEADLOCK 两个部分
3. information_shcema下的三张表(通过这三张表可以更新监控当前事物并且分析存在的锁问题)
—— innodb_trx ( 打印innodb内核中的当前活跃(ACTIVE)事务)
—— innodb_locks ( 打印当前状态产生的innodb锁 仅在有锁等待时打印)
—— innodb_lock_waits (打印当前状态产生的innodb锁等待 仅在有锁等待时打印)
1) innodb_trx表结构说明 (摘取最能说明问题的8个字段)
字段名 | 说明 |
trx_id | innodb存储引擎内部唯一的事物ID |
trx_state | 当前事物状态(running和lock wait两种状态) |
trx_started | 事物的开始时间 |
trx_requested_lock_id | 等待事物的锁ID,如trx_state的状态为Lock wait,那么该值带表当前事物等待之前事物占用资源的ID,若trx_state不是Lock wait 则该值为NULL |
trx_wait_started | 事物等待的开始时间 |
trx_weight | 事物的权重,在innodb存储引擎中,当发生死锁需要回滚的时,innodb存储引擎会选择该值最小的进行回滚 |
trx_mysql_thread_id | mysql中的线程id, 即show processlist显示的结果 |
trx_query | 事物运行的SQL语句 |
2)innodb_locks表结构说明
字段名 | 说明 |
lock_id | 锁的ID |
lock_trx_id | 事物的ID |
lock_mode | 锁的模式(S锁与X锁两种模式) |
lock_type | 锁的类型 表锁还是行锁(RECORD) |
lock_table | 要加锁的表 |
lock_index | 锁住的索引 |
lock_space | 锁住对象的space id |
lock_page | 事物锁定页的数量,若是表锁则该值为NULL |
lock_rec | 事物锁定行的数量,若是表锁则该值为NULL |
lock_data | 事物锁定记录主键值,若是表锁则该值为NULL(此选项不可信) |
3)innodb_lock_waits表结构说明
字段名 | 说明 |
requesting_trx_id | 申请锁资源的事物ID |
requested_lock_id | 申请的锁的ID |
blocking_trx_id | 阻塞其他事物的事物ID |
blocking_lock_id | 阻塞其他锁的锁ID |
可以根据这三张表进行联合查询,得到更直观更清晰的结果,可以参考如下SQL(可根据自己的分析习惯适进行调整)
select
r.trx_isolation_level,
r.trx_id waiting_trx_id,
r.trx_mysql_thread_id waiting_trx_thread,
r.trx_state waiting_trx_state,
lr.lock_mode waiting_trx_lock_mode,
lr.lock_type waiting_trx_lock_type,
lr.lock_table waiting_trx_lock_table,
lr.lock_index waiting_trx_lock_index,
r.trx_query waiting_trx_query,
b.trx_id blocking_trx_id,
b.trx_mysql_thread_id blocking_trx_thread,
b.trx_state blocking_trx_state,
lb.lock_mode blocking_trx_lock_mode,
lb.lock_type blocking_trx_lock_type,
lb.lock_table blocking_trx_lock_table,
lb.lock_index blocking_trx_lock_index,
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
inner join information_schema.innodb_locks lb
on lb.lock_trx_id=w.blocking_trx_id
inner join information_schema.innodb_locks lr
on lr.lock_trx_id=w.requesting_trx_id\G;
*************************** 1. row ***************************
trx_isolation_level: REPEATABLE READ
waiting_trx_id: 2900247
waiting_trx_thread: 1070
waiting_trx_state: LOCK WAIT
waiting_trx_lock_mode: S
waiting_trx_lock_type: RECORD
waiting_trx_lock_table: `jiang_test`.`test`
waiting_trx_lock_index: PRIMARY
waiting_trx_query: select * from test where id=3 lock in share mode
blocking_trx_id: 2900241
blocking_trx_thread: 1137
blocking_trx_state: RUNNING
blocking_trx_lock_mode: X
blocking_trx_lock_type: RECORD
blocking_trx_lock_table: `jiang_test`.`test`
blocking_trx_lock_index: PRIMARY
blocking_query: NULL
1 row in set (0.01 sec)
4、可以通过检查InnoDB_row_lock状态变量来分析系统上的行锁的争夺情况:
mysql> show status like 'innodb_row_lock%';
+-------------------------------+-------+
| Variable_name | Value |
+-------------------------------+-------+
| InnoDB_row_lock_current_waits | 0 |
| InnoDB_row_lock_time | 0 |
| InnoDB_row_lock_time_avg | 0 |
| InnoDB_row_lock_time_max | 0 |
| InnoDB_row_lock_waits | 0 |
+-------------------------------+-------+
5 rows in set (0.01 sec)
如果发现锁争用比较严重,如InnoDB_row_lock_waits和InnoDB_row_lock_time_avg的值比较高,还可以通过设置InnoDB Monitors来进一步观察发生锁冲突的表、数据行等,并分析锁争用的原因。
具体方法如下:
mysql> CREATE TABLE innodb_monitor(a INT) ENGINE=INNODB;
Query OK, 0 rows affected (0.14 sec)
然后就可以用下面的语句来进行查看:
mysql> Show innodb status\G;
*************************** 1. row ***************************
Type: InnoDB
Name:
Status:
…
…
------------
TRANSACTIONS
------------
Trx id counter 0 117472192
Purge done for trx's n:o < 0 117472190 undo n:o < 0 0
History list length 17
Total number of lock structs in row lock hash table 0
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0 117472185, not started, process no 11052, OS thread id 1158191456
MySQL thread id 200610, query id 291197 localhost root
---TRANSACTION 0 117472183, not started, process no 11052, OS thread id 1158723936
MySQL thread id 199285, query id 291199 localhost root
Show innodb status
…
监视器可以通过发出下列语句来停止查看:
mysql> DROP TABLE innodb_monitor;
Query OK, 0 rows affected (0.05 sec)
设置监视器后,在SHOW INNODB STATUS的显示内容中,会有详细的当前锁等待的信息,包括表名、锁类型、锁定记录的情况等,便于进行进一步的分析和问题的确定。打开监视器以后,默认情况下每15秒会向日志中记录监控的内容,如果长时间打开会导致.err文件变得非常的巨大,所以用户在确认问题原因之后,要记得删除监控表以关闭监视器,或者通过使用“--console”选项来启动服务器以关闭写日志文件。