标签：mysql 锁 事务id
大家都知道,锁是阻碍读写的,锁越多,数据库性能就越差,所以我们要随时监测锁的问题.
当然根本问题还是要开发要控制好锁粒度,把where条件写好,这样才能减少锁的影响.
另外,死锁其实不可怕,因为mysql内部发现死锁会发生回滚操作,所以不会真的"死"了,可怕的是锁等待,一大堆语句等着某个语句释放锁,这才是严重阻碍效率的情况.
当然了,也不是说死锁的问题不重要,如果出现大量的死锁,那显然就是业务逻辑的问题了,需要和开发人员好好谈谈,不是随便谁谁能解决的事情.
现在我们来看看锁的信息是怎么看的,
首先,我们知道mysql有四种隔离级别,不同隔离级别,锁的等级也不一样,所以,查看锁的信息之前一定要先看当前的隔离级别是什么.
mysql> select @@global.tx_isolation,@@tx_isolation;
+-----------------------+-----------------+
| @@global.tx_isolation | @@tx_isolation |
+-----------------------+-----------------+
| REPEATABLE-READ | REPEATABLE-READ |
+-----------------------+-----------------+
1 row in set (0.00 sec)
当前是RR的隔离级别
mysql里面有一个库information_schema,是专门记录mysql性能信息的地方,包括事务ID,锁信息,锁等待时间,缓存使用情况等等信息,现在我们只看我们需要的信息.
查看事务ID,会显示是什么操作和一些常规信息,例如是否在运行running,还是等待锁.
SELECT * FROM information_schema.INNODB_TRX\G;
查看当前锁的信息,会显示是什么锁类型,属于那个事务ID
SELECT * FROM information_schema.innodb_locks\G;
查看锁的等待时间,和等待的是那的是那个事务ID的锁
select * from information_schema.innodb_lock_waits\G
查看metadata lock信息,即元数据锁,这种锁会让任何语句都不能操作这个表,包括表结构
select * from information_schema.processlist where state = ‘Waiting for table metadata lock‘;
上面这些语句要是查不到数据,那就证明当前没有响应的锁信息,查到了那就是有了.
要想查询历史数据来统计性能,可以用下面这两个语句来计算,计算方法可以另外查查
show status like ‘%lock%‘;
show variables like ‘%timeout%‘;
查询死锁的信息的语句
show engine innodb status\G
如果有DEADLOCK标识,也就是说出现过死锁,如果没有,也就是没出现过,而mysql只会记录最后一个死锁,不是只记录一个,所以你能看到的死锁语句只有一条,这个要注意一下.
很多时我们说假如有个锁等待实在太长,已经不想去执行他,但是他严重阻碍了后面重要语句的执行,那怎么办呢?虽然说能kill掉语句,但是又不确定那条跟他有关系,所以就很头痛,这个时候可以用下面这条语句
select `r`.`trx_wait_started` AS `wait_started`,timediff(now(),`r`.`trx_wait_started`) AS `wait_age`,timestampdiff(SECOND,`r`.`trx_wait_started`,now()) AS `wait_age_secs`,`rl`.`lock_table` AS `locked_table`,`rl`.`lock_index` AS `locked_index`,`rl`.`lock_type` AS `locked_type`,`r`.`trx_id` AS `waiting_trx_id`,`r`.`trx_started` AS `waiting_trx_started`,timediff(now(),`r`.`trx_started`) AS `waiting_trx_age`,`r`.`trx_rows_locked` AS `waiting_trx_rows_locked`,`r`.`trx_rows_modified` AS `waiting_trx_rows_modified`,`r`.`trx_mysql_thread_id` AS `waiting_pid`, `r`.`trx_query` AS `waiting_query`,`rl`.`lock_id` AS `waiting_lock_id`,`rl`.`lock_mode` AS `waiting_lock_mode`,`b`.`trx_id` AS `blocking_trx_id`,`b`.`trx_mysql_thread_id` AS `blocking_pid`, `b`.`trx_query` AS `blocking_query`,`bl`.`lock_id` AS `blocking_lock_id`,`bl`.`lock_mode` AS `blocking_lock_mode`,`b`.`trx_started` AS `blocking_trx_started`,timediff(now(),`b`.`trx_started`) AS `blocking_trx_age`,`b`.`trx_rows_locked` AS `blocking_trx_rows_locked`,`b`.`trx_rows_modified` AS `blocking_trx_rows_modified`,concat(‘KILL QUERY ‘,`b`.`trx_mysql_thread_id`) AS `sql_kill_blocking_query`,concat(‘KILL ‘,`b`.`trx_mysql_thread_id`) AS `sql_kill_blocking_connection` from ((((`information_schema`.`innodb_lock_waits` `w` join `information_schema`.`innodb_trx` `b` on((`b`.`trx_id` = `w`.`blocking_trx_id`))) join `information_schema`.`innodb_trx` `r` on((`r`.`trx_id` = `w`.`requesting_trx_id`))) join `information_schema`.`innodb_locks` `bl` on((`bl`.`lock_id` = `w`.`blocking_lock_id`))) join `information_schema`.`innodb_locks` `rl` on((`rl`.`lock_id` = `w`.`requested_lock_id`))) order by `r`.`trx_wait_started`\G
这条语句会计算出当前锁的关联信息,如果你不想那个锁继续执行,那就执行最后显示的kill命令就可以了.
附录一些information_schema 表结构的信息
information_schema > desc innodb_locks;
+-------------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+---------------------+------+-----+---------+-------+
| lock_id | varchar(81) | NO | | | |#锁ID
| lock_trx_id | varchar(18) | NO | | | |#拥有锁的事务ID
| lock_mode | varchar(32) | NO | | | |#锁模式
| lock_type | varchar(32) | NO | | | |#锁类型
| lock_table | varchar(1024) | NO | | | |#被锁的表
| lock_index | varchar(1024) | YES | | NULL | |#被锁的索引
| lock_space | bigint(21) unsigned | YES | | NULL | |#被锁的表空间号
| lock_page | bigint(21) unsigned | YES | | NULL | |#被锁的页号
| lock_rec | bigint(21) unsigned | YES | | NULL | |#被锁的记录号
| lock_data | varchar(8192) | YES | | NULL | |#被锁的数据
+-------------+---------------------+------+-----+---------+-------+
10 rows in set (0.00 sec)
information_schema > desc innodb_lock_waits;
+-------------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------------+-------------+------+-----+---------+-------+
| requesting_trx_id | varchar(18) | NO | | | |#请求锁的事务ID
| requested_lock_id | varchar(81) | NO | | | |#请求锁的锁ID
| blocking_trx_id | varchar(18) | NO | | | |#当前拥有锁的事务ID
| blocking_lock_id | varchar(81) | NO | | | |#当前拥有锁的锁ID
+-------------------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
information_schema > desc innodb_trx ;
+----------------------------+---------------------+------+-----+---------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------------------------+---------------------+------+-----+---------------------+-------+
| trx_id | varchar(18) | NO | | | |#事务ID
| trx_state | varchar(13) | NO | | | |#事务状态：
| trx_started | datetime | NO | | 0000-00-00 00:00:00 | |#事务开始时间；
| trx_requested_lock_id | varchar(81) | YES | | NULL | |#innodb_locks.lock_id
| trx_wait_started | datetime | YES | | NULL | |#事务开始等待的时间
| trx_weight | bigint(21) unsigned | NO | | 0 | |#
| trx_mysql_thread_id | bigint(21) unsigned | NO | | 0 | |#事务线程ID
| trx_query | varchar(1024) | YES | | NULL | |#具体SQL语句
| trx_operation_state | varchar(64) | YES | | NULL | |#事务当前操作状态
| trx_tables_in_use | bigint(21) unsigned | NO | | 0 | |#事务中有多少个表被使用
| trx_tables_locked | bigint(21) unsigned | NO | | 0 | |#事务拥有多少个锁
| trx_lock_structs | bigint(21) unsigned | NO | | 0 | |#
| trx_lock_memory_bytes | bigint(21) unsigned | NO | | 0 | |#事务锁住的内存大小（B）
| trx_rows_locked | bigint(21) unsigned | NO | | 0 | |#事务锁住的行数
| trx_rows_modified | bigint(21) unsigned | NO | | 0 | |#事务更改的行数
| trx_concurrency_tickets | bigint(21) unsigned | NO | | 0 | |#事务并发票数
| trx_isolation_level | varchar(16) | NO | | | |#事务隔离级别
| trx_unique_checks | int(1) | NO | | 0 | |#是否唯一性检查
| trx_foreign_key_checks | int(1) | NO | | 0 | |#是否外键检查
| trx_last_foreign_key_error | varchar(256) | YES | | NULL | |#最后的外键错误
| trx_adaptive_hash_latched | int(1) | NO | | 0 | |#
| trx_adaptive_hash_timeout | bigint(21) unsigned | NO | | 0 | |#
+----------------------------+---------------------+------+-----+---------------------+-------+
22 rows in set (0.01 sec)
标签：mysql 锁 事务id
原文地址：http://arthur376.blog.51cto.com/2918801/1773050
