MySQL锁情况查看命令
挠背小能手 人气:0本文介绍如何在MySQL数据库中分析锁的情况及处理思路。
MySQL版本
mysql> select version(); +------------+ | version() | +------------+ | 5.7.38-log | +------------+ 1 row in set (0.01 sec)
模拟锁产生
A会话加锁
mysql> show create table t\G; *************************** 1. row *************************** Table: t Create Table: CREATE TABLE `t` ( `id` int(11) NOT NULL, `name` varchar(10) COLLATE utf8mb4_unicode_ci DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci 1 row in set (0.00 sec) ERROR: No query specified mysql> select * from t; +----+------+ | id | name | +----+------+ | 1 | a | | 2 | s | | 3 | c | | 4 | d | | 5 | e | +----+------+ 5 rows in set (0.00 sec) mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select * from t where id<5 for update; +----+------+ | id | name | +----+------+ | 1 | a | | 2 | s | | 3 | c | | 4 | d | +----+------+ 4 rows in set (0.00 sec)
B会话插入数据，造成锁等待现象
mysql> insert into t values(0,'null');
这里介绍MySQL查看锁的3个数据字典表，分别是位于information_schema数据库下的innodb_trx、innodb_lock_waits、innodb_locks三张表，查看步骤如下：
先看innodb_trx表
mysql> use information_schema; 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> select * from innodb_trx\G; *************************** 1. row *************************** trx_id: 8553 trx_state: LOCK WAIT trx_started: 2022-12-14 16:52:29 trx_requested_lock_id: 8553:45:3:2 trx_wait_started: 2022-12-14 16:52:29 trx_weight: 2 trx_mysql_thread_id: 22 trx_query: insert into t values(0,'null') trx_operation_state: inserting trx_tables_in_use: 1 trx_tables_locked: 1 trx_lock_structs: 2 trx_lock_memory_bytes: 1136 trx_rows_locked: 1 trx_rows_modified: 0 trx_concurrency_tickets: 0 trx_isolation_level: REPEATABLE READ trx_unique_checks: 1 trx_foreign_key_checks: 1 trx_last_foreign_key_error: NULL trx_adaptive_hash_latched: 0 trx_adaptive_hash_timeout: 0 trx_is_read_only: 0 trx_autocommit_non_locking: 0 *************************** 2. row *************************** trx_id: 8552 trx_state: RUNNING trx_started: 2022-12-14 16:51:39 trx_requested_lock_id: NULL trx_wait_started: NULL trx_weight: 2 trx_mysql_thread_id: 20 trx_query: NULL trx_operation_state: NULL trx_tables_in_use: 0 trx_tables_locked: 1 trx_lock_structs: 2 trx_lock_memory_bytes: 1136 trx_rows_locked: 5 trx_rows_modified: 0 trx_concurrency_tickets: 0 trx_isolation_level: REPEATABLE READ trx_unique_checks: 1 trx_foreign_key_checks: 1 trx_last_foreign_key_error: NULL trx_adaptive_hash_latched: 0 trx_adaptive_hash_timeout: 0 trx_is_read_only: 0 trx_autocommit_non_locking: 0 2 rows in set (0.00 sec) ERROR: No query specified mysql> show full processlist; +----+--------+-----------+--------------------+---------+------+----------+--------------------------------+ | Id | User | Host | db | Command | Time | State | Info | +----+--------+-----------+--------------------+---------+------+----------+--------------------------------+ | 20 | root | localhost | ray | Sleep | 132 | | NULL | | 22 | raybak | localhost | ray | Query | 82 | update | insert into t values(0,'null') | | 24 | root | localhost | information_schema | Query | 0 | starting | show full processlist | +----+--------+-----------+--------------------+---------+------+----------+--------------------------------+ 3 rows in set (0.00 sec)
trx_id：唯一事务id号，本次测试中是8552和8553
trx_state：当前事务的状态，本次测试中8553是LOCK WAIT 锁等待状态
trx_wait_started：事务开始等待时间，本次测试中为2022-12-14 16:52:29
trx_mysql_thread_id：线程id，与show full processlist中的id对应，本次测试中为22
trx_query：事务运行的SQL语句，本次测试为insert into t values(0,‘null’)
trx_operation_state：事务运行的状态，本次测试为inserting
再看innodb_lock_waits表
mysql> select * from innodb_lock_waits\G; *************************** 1. row *************************** requesting_trx_id: 8553 requested_lock_id: 8553:45:3:2 blocking_trx_id: 8552 blocking_lock_id: 8552:45:3:2 1 row in set, 1 warning (0.00 sec)
requesting_trx_id：请求锁的事务id，本次测试为8553
blocking_trx_id：持有锁的事务id，也就是造成锁等待的事务id，本次测试为8552
再看innodb_locks表
mysql> select * from innodb_locks\G; *************************** 1. row *************************** lock_id: 8553:45:3:2 lock_trx_id: 8553 lock_mode: X,GAP lock_type: RECORD lock_table: `ray`.`t` lock_index: PRIMARY lock_space: 45 lock_page: 3 lock_rec: 2 lock_data: 1 *************************** 2. row *************************** lock_id: 8552:45:3:2 lock_trx_id: 8552 lock_mode: X lock_type: RECORD lock_table: `ray`.`t` lock_index: PRIMARY lock_space: 45 lock_page: 3 lock_rec: 2 lock_data: 1 2 rows in set, 1 warning (0.00 sec) ERROR: No query specified
综合三张表查询和show prcess fulllist得知，会话id 20（事务id 8552），锁住了ray.t表，锁模式是行级锁，会话id 22（事务id 8553）的insert操作需要等待会话20释放锁后才能执行，因此出现了会话id 22（事务id 8553）hang住现象。
解决方法，杀会话
mysql> kill 20; Query OK, 0 rows affected (0.00 sec)
当然，杀会话也可以通过pt-kill工具更方便，在后续文章会对pt-kill工具做详细介绍
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