[MySQL FAQ]系列 — 如何查看当前最新事务ID

InnoDB

写在前面:在个别时候可能需要查看当前最新的事务ID,以便做一些业务逻辑上的判断(例如利用事务ID变化以及前后时差,统计每次事务的响应时长等用途)。

通常地,我们有两种方法可以查看当前的事务ID:

1、执行SHOW ENGINE INNODB STATUS,查看事务相关信息

=====================================
150303 17:16:11 INNODB MONITOR OUTPUT
=====================================
Per second averages calculated from the last 15 seconds
...
------------
TRANSACTIONS
Trx id counter 3359877657 -- 当前最大事务ID
Purge done for trx's n:o < 3359877468 undo n:o < 0 state: running
History list length 324
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0, not started -- 该会话中执行SHOW ENGINE INNODB STATUS,不会产生事务,所以事务ID为0
MySQL thread id 4692367, OS thread handle 0x51103940, query id 677284426 xx.173ops.com 10.x.x.x yejr init
SHOW /*!50000 ENGINE*/ INNODB STATUS
---TRANSACTION 3359877640, not started --非活跃事务,还未开始
mysql tables in use 1, locked 0
MySQL thread id 4678384, OS thread handle 0x41a57940, query id 677284427 xx.173ops.com 10.x.x.x yejr System lock
select polinfo0_.Fid as Fid39_0_, ...

---TRANSACTION 3359877652, not started
MySQL thread id 4678383, OS thread handle 0x50866940, query id 677284420 xx.173ops.com 10.x.x.x yejr cleaning up

---TRANSACTION 3359877635, ACTIVE 1358 sec, thread declared inside InnoDB 5000 --活跃长事务,运行了1358秒还未结束,要引起注意,可能会导致大量锁等待发生
mysql tables in use 1, locked 1
1 lock struct(s), heap size 376, 0 row lock(s), undo log entries 1
MySQL thread id 3120717, OS thread handle 0x529b4940, query id 677284351 xx.173ops.com 10.x.x.x yejr query end
insert into t_live_room ...

 

2、查看INFORMATION_SCHEMA.INNODB_TRX、INNODB_LOCKS、INNODB_LOCK_WAITS 三个表,通过这些信息能快速发现哪些事务在阻塞其他事务

#先查询 INNODB_TRX 表,看看都有哪些事务

mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_TRX\G
*************************** 1. row ***************************
 trx_id: 17778 -- 当前事务ID
 trx_state: LOCK WAIT -- 处于锁等待状态,也就是等待其他会话释放锁资源
 trx_started: 2015-03-04 10:40:26
 trx_requested_lock_id: 17778:82:3:6 -- 欲请求的锁
 trx_wait_started: 2015-03-04 10:40:26
 trx_weight: 2 -- 大意是该锁影响了2行记录
 trx_mysql_thread_id: 657 -- processlist中的线程ID
 trx_query: update trx_fee set fee=rand()*1000 where id= 4
 trx_operation_state: starting index read
 trx_tables_in_use: 1
 trx_tables_locked: 1
 trx_lock_structs: 2
 trx_lock_memory_bytes: 360
 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: 10000
 trx_is_read_only: 0
 trx_autocommit_non_locking: 0
 *************************** 2. row ***************************
 trx_id: 17773
  trx_state: RUNNING
 trx_started: 2015-03-04 10:40:23
 trx_requested_lock_id: NULL
 trx_wait_started: NULL
 trx_weight: 10
 trx_mysql_thread_id: 656
 trx_query: NULL
 trx_operation_state: NULL
 trx_tables_in_use: 0
 trx_tables_locked: 0
 trx_lock_structs: 2
 trx_lock_memory_bytes: 360
 trx_rows_locked: 9
 trx_rows_modified: 8
 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

 

#再看 INNODB_LOCKS 表,看看都有什么锁

mysql> select * from information_schema.INNODB_LOCKS\G
*************************** 1. row ***************************
lock_id: 17778:82:3:6 --当前锁ID
lock_trx_id: 17778 --该锁对应的事务ID
lock_mode: X -- 锁类型,排它锁X
lock_type: RECORD --锁范围,记录锁:record lock,其他锁范围:间隙锁:gap lock,或者next-key lock(记录锁+间隙锁)
lock_table: `test`.`trx_fee`
lock_index: PRIMARY --加载在哪个索引上的锁
lock_space: 82
lock_page: 3
lock_rec: 6
lock_data: 4
*************************** 2. row ***************************
lock_id: 17773:82:3:6
lock_trx_id: 17773
lock_mode: X
lock_type: RECORD
lock_table: `test`.`trx_fee`
lock_index: PRIMARY
lock_space: 82
lock_page: 3
lock_rec: 6
lock_data: 4

 

#最后看 INNODB_LOCK_WAITS 表,看看当前都有哪些锁等待

mysql> select * from information_schema.INNODB_LOCK_WAITS\G
*************************** 1. row ***************************
requesting_trx_id: 17778 --请求锁的事务ID(等待方)
requested_lock_id: 17778:82:3:6 -- 请求锁ID
blocking_trx_id: 17773 -- 阻塞该锁的事务ID(当前持有方,待释放)
blocking_lock_id: 17773:82:3:6 -- 持有的锁ID

关于INFORMATION_SCHEMA中和InnoDB有关的表用途描述,可以查看手册:21.29 INFORMATION_SCHEMA Tables for InnoDB

 

3、利用percona分支的特性,查看当前最新事务ID,该特性从5.6.11-60.3版本开始引入,执行下面的2个命令即可查看

mysqladmin ext | grep Innodb_max_trx_id
或者
mysql> show global status like 'Innodb_max_trx_id';

最后,交代下问题的来源其实是这样的,有位朋友和我讨论问题,说在java连接池中,发现2个事务的事务ID是一样的,测试的SQL代码:

begin;update trx set un=rand() where id=round(rand()*10)+1;select * from information_schema.INNODB_TRX; commit;select sleep(0.01);begin;update trx set un=rand() where id=round(rand()*10)+1;select * from information_schema.INNODB_TRX;commit;

这串代码不能折行,中间的 sleep 停留 不能太大,也就是模拟足够快的情况下,检查2次事务的ID是否有变化。可以发现,时间足够短的话,2次查询到的事务ID是一样的,并没有发生变化。大家也可以在自己的环境下试试。

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