MySQL找出未提交事务的信息

用户1148526

发布于 2020-03-31 15:52:16

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发布于 2020-03-31 15:52:16

我们经常会碰到这样的情况，某个事务执行完了未提交，后续再来一个DDL和DML操作，导致后面的session要么处于waiting for metadata lock，要么是锁等待超时。这时我们往往只能找到这个未提交的事务的事务id和session id，但是一般都处于sleep状态，不好分析事务内容到底是什么，所以通常都是粗鲁地kill这个session后解决问题，但是应用层的研发人员往往找不到到底是哪个事务引起的，后面再出现问题时还要重复kill。

一、processlist中的未提交事务

对于一个执行完但未提交的事务，无法在show processlist的输出中找到该信息：

-- session 1
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)

mysql> use test;
Database changed
mysql> create table t1(a int);
Query OK, 0 rows affected (0.45 sec)

mysql> insert into t1 values (1);
Query OK, 1 row affected (0.00 sec)

mysql> select connection_id() from dual;
+-----------------+
| connection_id() |
+-----------------+
|               6 |
+-----------------+
1 row in set (0.00 sec)

-- session 2
mysql> show processlist;
+----+------+-----------+------+---------+------+-------+------------------+
| Id | User | Host      | db   | Command | Time | State | Info             |
+----+------+-----------+------+---------+------+-------+------------------+
|  6 | root | localhost | test | Sleep   |   44 |       | NULL             |
|  7 | root | localhost | NULL | Query   |    0 | init  | show processlist |
+----+------+-----------+------+---------+------+-------+------------------+
2 rows in set (0.00 sec)

可以看到，未提交事务的Command为Sleep，State为空，Info为NULL。

二、information_schema.innodb_trx中的未提交事务

同样，information_schema.innodb_trx.trx_query也为NULL，无法提供未提交事务的SQL语句：

mysql> select * from information_schema.innodb_trx\G
*************************** 1. row ***************************
                    trx_id: 4632
                 trx_state: RUNNING
               trx_started: 2020-03-28 07:18:32
     trx_requested_lock_id: NULL
          trx_wait_started: NULL
                trx_weight: 2
       trx_mysql_thread_id: 6
                 trx_query: NULL
       trx_operation_state: NULL
         trx_tables_in_use: 0
         trx_tables_locked: 0
          trx_lock_structs: 1
     trx_lock_memory_bytes: 376
           trx_rows_locked: 0
         trx_rows_modified: 1
   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 (0.00 sec)

三、performance_schema.events_statements_current中的未提交事务

通过查看performance_schema.events_statements_current表可看到每一个session正在执行的sql，哪怕它依旧执行完成了，只是没有提交：

mysql> select * from performance_schema.events_statements_current where sql_text not like 'select * from performance_schema.events_statements_current%'\G
*************************** 1. row ***************************
              THREAD_ID: 25
               EVENT_ID: 9
           END_EVENT_ID: 9
             EVENT_NAME: statement/sql/select
                 SOURCE: mysqld.cc:937
            TIMER_START: 1897350780117784000
              TIMER_END: 1897350780310674000
             TIMER_WAIT: 192890000
              LOCK_TIME: 0
               SQL_TEXT: select connection_id() from dual
                 DIGEST: e5d97521478adc05b74560b51be5d6f7
            DIGEST_TEXT: SELECT `connection_id` ( ) FROM DUAL 
         CURRENT_SCHEMA: test
            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: 1
          ROWS_EXAMINED: 0
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: 0
      SORT_MERGE_PASSES: 0
             SORT_RANGE: 0
              SORT_ROWS: 0
              SORT_SCAN: 0
          NO_INDEX_USED: 0
     NO_GOOD_INDEX_USED: 0
       NESTING_EVENT_ID: NULL
     NESTING_EVENT_TYPE: NULL
1 row in set (0.00 sec)

该方案有一个缺陷：一个事务可能有一组sql组成，这个方法只能看到事务最后执行的是什么SQL，无法看到全部。可以通过performance_schema.threads表来关联，将information_schema.processlist和performance_schema.events_statements_current一一对应起来：

mysql> select t1.id, t2.thread_id, t3.sql_text
    ->   from information_schema.processlist t1, 
    ->        performance_schema.threads t2,
    ->        performance_schema.events_statements_current t3
    ->  where t1.id=6
    ->    and t1.id=t2.processlist_id 
    ->    and t2.thread_id = t3.thread_id\G
*************************** 1. row ***************************
       id: 6
thread_id: 25
 sql_text: select connection_id() from dual
1 row in set (0.00 sec)

参考：

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