随笔：MySQL 查询事务状态字段说明

今天一个朋友想查看一下的MySQL层事务提交状态经历的过程，比如我们常说的prapare flush sync commit 几个阶段，但是找了一下发现视乎没有视图可以看到一共看了3个地方：

• information_schema.INNODB_TRX 的trx_state字段
• information_schema.INNODB_TRX 的trx_operation_state字段
• performance_schema.events_transactions_current 的STATE字段

其中information_schema.INNODB_TRX表由函数fill_innodb_trx_from_cache进行填充，最终发现他们均不能满足需求。

欢迎关注我的《深入理解MySQL主从原理 32讲 》，如下：

一、information_schema.INNODB_TRX 的trx_state字段

这个字段源码注释如下：

    trx_que_t    que_state;    /*!< valid when trx->state
                    == TRX_STATE_ACTIVE: TRX_QUE_RUNNING,
                    TRX_QUE_LOCK_WAIT, ... */
/** Transaction execution states when trx->state == TRX_STATE_ACTIVE */
enum trx_que_t {
    TRX_QUE_RUNNING,        /*!< transaction is running */
    TRX_QUE_LOCK_WAIT,        /*!< transaction is waiting for
                    a lock */
    TRX_QUE_ROLLING_BACK,        /*!< transaction is rolling back */
    TRX_QUE_COMMITTING        /*!< transaction is committing */
};

在测试中发现即便是commit下的也会是RUNNING状态，如下：

因此主要取值有3个

• TRX_QUE_RUNNING RUNNING
• TRX_QUE_LOCK_WAIT LOCK WAIT
• TRX_QUE_ROLLING_BACK ROLLING BACK

但是COMMITTING状态正确commit流程不触发。

二、information_schema.INNODB_TRX 的trx_operation_state字段

这个字段取值很多，标记了事务的各个阶段，主要来自于trx_t::op_info，在commit阶段有如下取值：

其中preparing 和committing分别由函数trx_prepare_for_mysql和trx_commit_for_mysql进入，做完innodb层的prepare和commit后就会更改为NULL，实际的binlog的flush sync阶段不包含其中，实际也很好测试，可以做一个大事务，会发现 commit期间基本处于NULL状态：

mysql> select * from  information_schema.INNODB_TRX \G
*************************** 1. row ***************************
                    trx_id: 66206
                 trx_state: RUNNING
               trx_started: 2019-08-23 23:44:05
     trx_requested_lock_id: NULL
          trx_wait_started: NULL
                trx_weight: 1046257
       trx_mysql_thread_id: 4
                 trx_query: commit
       trx_operation_state: NULL
         trx_tables_in_use: 0
         trx_tables_locked: 1
          trx_lock_structs: 2025
     trx_lock_memory_bytes: 319960
           trx_rows_locked: 1044232
         trx_rows_modified: 1044232
   trx_concurrency_tickets: 0
       trx_isolation_level: READ COMMITTED
...

三、performance_schema.events_transactions_current 的STATE字段

这个值也只有3个取值：

enum enum_transaction_state
{
  TRANS_STATE_ACTIVE= 1,
  TRANS_STATE_COMMITTED= 2,
  TRANS_STATE_ROLLED_BACK= 3
};

TRANS_STATE_ACTIVE到TRANS_STATE_COMMITTED的转换会出现在innodb层提交完成后，也就是这个时候实际上整个prapare flush sync commit 已经结束了，之前一直除以ACTIVE状态，用处不大。如下：

#0  pfs_end_transaction_v1 (locker=0x7ffee0014ba8, commit=1 '\001') at /mysqldata/percona-server-locks-detail-5.7.22/storage/perfschema/pfs.cc:6116
#1  0x0000000000f7d177 in inline_mysql_commit_transaction (locker=0x7ffee0014ba8)
    at /mysqldata/percona-server-locks-detail-5.7.22/include/mysql/psi/mysql_transaction.h:206
#2  0x0000000000f8026c in ha_commit_trans (thd=0x7ffee00129d0, all=true, ignore_global_read_lock=false)
    at /mysqldata/percona-server-locks-detail-5.7.22/sql/handler.cc:1843
#3  0x00000000016dcd2f in trans_commit (thd=0x7ffee00129d0) at /mysqldata/percona-server-locks-detail-5.7.22/sql/transaction.cc:239
#4  0x00000000015cf466 in mysql_execute_command (thd=0x7ffee00129d0, first_level=true) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:4526
#5  0x00000000015d2fde in mysql_parse (thd=0x7ffee00129d0, parser_state=0x7fffec5ee600) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:5901
#6  0x00000000015c6b72 in dispatch_command (thd=0x7ffee00129d0, com_data=0x7fffec5eed70, command=COM_QUERY)
    at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:1490
#7  0x00000000015c58ff in do_command (thd=0x7ffee00129d0) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:1021
#8  0x000000000170e578 in handle_connection (arg=0x67d6410) at /mysqldata/percona-server-locks-detail-5.7.22/sql/conn_handler/connection_handler_per_thread.cc:312
#9  0x0000000001945538 in pfs_spawn_thread (arg=0x67be520) at /mysqldata/percona-server-locks-detail-5.7.22/storage/perfschema/pfs.cc:2190
#10 0x00007ffff7bcfaa1 in start_thread () from /lib64/libpthread.so.0
#11 0x00007ffff6b37c4d in clone () from /lib64/libc.so.6
(gdb) n
6117      DBUG_ASSERT(state != NULL);
(gdb) n
6119      ulonglong timer_end= 0;
(gdb) n
6120      ulonglong wait_time= 0;
(gdb) n
6121      uint flags= state->m_flags;
(gdb) n
6123      if (flags & STATE_FLAG_TIMED)
(gdb) n
6125        timer_end= state->m_timer();
(gdb) n
6126        wait_time= timer_end - state->m_timer_start;
(gdb) n
6131      if (flags & STATE_FLAG_THREAD)
(gdb) n
6133        PFS_thread *pfs_thread= reinterpret_cast<PFS_thread *> (state->m_thread);
(gdb) n
6134        DBUG_ASSERT(pfs_thread != NULL);
(gdb) n
6137        stat= &pfs_thread->write_instr_class_transactions_stats()[GLOBAL_TRANSACTION_INDEX];
(gdb) n
6139        if (flags & STATE_FLAG_EVENT)
(gdb) n
6141          PFS_events_transactions *pfs= reinterpret_cast<PFS_events_transactions*> (state->m_transaction);
(gdb) n
6142          DBUG_ASSERT(pfs != NULL);
(gdb) n
6145          if (unlikely(pfs->m_class == NULL))
(gdb) n
6148          pfs->m_timer_end= timer_end;
(gdb) n
6149          pfs->m_end_event_id= pfs_thread->m_event_id;
(gdb) n
6151          pfs->m_state= (commit ? TRANS_STATE_COMMITTED : TRANS_STATE_ROLLED_BACK);
(gdb) p pfs->m_state
$1 = TRANS_STATE_ACTIVE

因此上面3个取值都不是那么有用。