MySQL如何查看元数据锁阻塞在哪里

mysql/' target='_blank'>mysql如何查看元数据锁阻塞在哪里

操作步骤：

1、session 1 执行：

   start transaction;   select *from t1;

2、session 2 在第1步执行完后执行：

  drop table t1;

此时session 2的drop语句被阻塞。那么怎么分析查看元数据锁呢？

方法：

1）执行show processlist;，可以看到drop语句在等待元数据锁

MySQL> show processlist; +----+-------------+-----------+------+---------+---------+-----------------------------------------------------------------------------+------------------+ | Id | User    | Host   | db  | Command | Time  | State                                    | Info       | +----+-------------+-----------+------+---------+---------+-----------------------------------------------------------------------------+------------------+ | 5 | system user |      | NULL | Connect | 1050234 | Waiting for master to send event                      | NULL       | | 6 | system user |      | NULL | Connect | 983193 | Slave has read all relay log; waiting for the slave I/O thread to update it | NULL       | | 8 | root    | localhost | yzs | Sleep  |   93 |                                       | NULL       | | 9 | root    | localhost | yzs | Query  |    3 | Waiting for table metadata lock                       | drop table t1  | | 10 | root    | localhost | NULL | Query  |    0 | init                                    | show processlist | +----+-------------+-----------+------+---------+---------+-----------------------------------------------------------------------------+------------------+ 5 rows in set (0.00 sec) 

2）可以看到当前正在运行的事务的线程是trx_mysql_thread_id:8，那么这个线程在干什么呢？

mysql> select *from information_schema.innodb_trx\G *************************** 1. row ***************************           trx_id: 17683          trx_state: RUNNING         trx_started: 2017-10-18 05:32:46    trx_requested_lock_id: NULL      trx_wait_started: NULL         trx_weight: 0     trx_mysql_thread_id: 8          trx_query: NULL     trx_operation_state: NULL      trx_tables_in_use: 0      trx_tables_locked: 0      trx_lock_structs: 0    trx_lock_memory_bytes: 320       trx_rows_locked: 0      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: 10000      trx_is_read_only: 0 trx_autocommit_non_locking: 0 1 row in set (0.03 sec) 

3）可以看到这个线程执行的是select语句，如果执行show engine innodb status;可以看到该事务处于sleep状态，也就是说这个事务语句执行完了，但是没有提交。

执行kill 8，将该事务的线程杀掉就可以了。或者检查业务的SQL语句，检查下是否有未提交的SQL语句。

mysql> select *from performance_schema.events_statements_current\G *************************** 1. row ***************************        THREAD_ID: 27         EVENT_ID: 15       END_EVENT_ID: 15        EVENT_NAME: statement/sql/select          SOURCE: mysqld.cc:962       TIMER_START: 1050544992900922000        TIMER_END: 1050544993740836000        TIMER_WAIT: 839914000        LOCK_TIME: 196000000         SQL_TEXT: select *from t1          DIGEST: 1aa32397c8ec37230aed78ef16126571       DIGEST_TEXT: SELECT * FROM `t1`       CURRENT_SCHEMA: yzs       OBJECT_TYPE: NULL      OBJECT_SCHEMA: NULL       OBJECT_NAME: NULL  OBJECT_INSTANCE_BEGIN: NULL       MYSQL_ERRNO: 0    RETURNED_SQLSTATE: NULL       MESSAGE_TEXT: NULL          ERRORS: 0         WARNINGS: 0      ROWS_AFFECTED: 0        ROWS_SENT: 10      ROWS_EXAMINED: 10 CREATED_TMP_DISK_TABLES: 0    CREATED_TMP_TABLES: 0     SELECT_FULL_JOIN: 0  SELECT_FULL_RANGE_JOIN: 0       SELECT_RANGE: 0    SELECT_RANGE_CHECK: 0       SELECT_SCAN: 1    SORT_MERGE_PASSES: 0        SORT_RANGE: 0        SORT_ROWS: 0        SORT_SCAN: 0      NO_INDEX_USED: 1    NO_GOOD_INDEX_USED: 0     NESTING_EVENT_ID: NULL    NESTING_EVENT_TYPE: NULL 

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