【MySQL】锁——查看当前数据库锁请求的三种方法 20
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)