今天我們主要看一下MySQL information_schema里面的關於innodb的鎖和事物的兩三個系統表:
看一下鎖對應的sql:
select * from innodb_lock_waits; select * from innodb_locks limit 2\G select * from information_schema.innodb_trx\G select * from information_schema.innodb_trx where trx_id = 45734628\G SELECT lw.requesting_trx_id AS request_ID, trx.trx_mysql_thread_id as request_mysql_ID, trx.trx_query AS request_command, lw.blocking_trx_id AS blocking_ID, trx1.trx_mysql_thread_id as blocking_mysql_ID, trx1.trx_query AS blocking_command, lo.lock_index AS lock_index FROM information_schema.innodb_lock_waits lw INNER JOIN information_schema.innodb_locks lo ON lw.requesting_trx_id = lo.lock_trx_id INNER JOIN information_schema.innodb_locks lo1 ON lw.blocking_trx_id = lo1.lock_trx_id INNER JOIN information_schema.innodb_trx trx ON lo.lock_trx_id = trx.trx_id INNER JOIN information_schema.innodb_trx trx1 ON lo1.lock_trx_id = trx1.trx_id;
1: INNODB_LOCKS
2: INNODB_TRX
3: INNODB_LOCK_WAITS
三張表就一起實驗好了,都是關於鎖和事物的阻塞的。我們現在開兩個終端。
第一個終端開啟一個事物,進行更新:
root@localhost [(none)]>start transaction; Query OK, 0 rows affected (0.00 sec) root@localhost [(none)]>update qiandai.t1 set col_int_key=333 where pk=10; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0
第二個終端直接也更新同一行數據:
update qiandai.t1 set col_int_key=222 where pk=10;
然后去查看三個表聯合查詢:

可以看得到,第二個更新是被阻塞的,因為第一個更新獲取到了排它鎖,所以第二個更新一致處於等待狀態,直到鎖等待時間超時:
SHOW VARIABLES LIKE '%LOCK_WAIT%';
上面可以查看到鎖等待的超時時間,INNODB默認五十秒。
看一下三個表官方給的解釋:
看一下三個表官方給的解釋:
INNODB_LOCK_WAITS:
https://dev.mysql.com/doc/refman/5.7/en/innodb-lock-waits-table.html