MySQL InnoDB設定死鎖檢測的方法

死鎖是指兩個或兩個以上的程式在執行過程中,因爭奪資源而造成的一種互相等待的現象,可以認為如果一個資源被鎖定，它總會在以後某個時間被釋放。而死鎖發生在當多個程式訪問同一資料庫時，其中每個程式擁有的鎖都是其他程式所需的，由此造成每個程式都無法繼續下去。
InnoDB的併發寫操作會觸發死鎖，InnoDB也提供了死鎖檢測機制，可以透過設定innodb_deadlock_detect引數可以開啟或關閉死鎖檢測:


innodb_deadlock_detect = on  開啟死鎖檢測，資料庫發生死鎖時自動回滾（預設選項）
innodb_deadlock_detect = off  關閉死鎖檢測，發生死鎖的時候，用鎖超時來處理，透過設定鎖超時引數innodb_lock_wait_timeout可以在超時發生時回滾被阻塞的事務


還可以透過設定InnDB Monitors來進一步觀察鎖衝突詳細資訊
設定InnoDB Monitors方法
建立test庫
mysql>create database test;
Query OK, 1 row affected (0.20 sec)
mysql> use test
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A


Database changed
mysql> create table innodb_monitor(a INT) engine=innodb;
Query OK, 0 rows affected (1.04 sec)


mysql> create table innodb_tablespace_monitor(a INT) engine=innodb;
Query OK, 0 rows affected (0.70 sec)


mysql> create table innodb_lock_monitor(a INT) engine=innodb;
Query OK, 0 rows affected (0.36 sec)


mysql> create table innodb_table_monitor(a INT) engine=innodb;
Query OK, 0 rows affected (0.08 sec)


可以透過show engine innodb status命令檢視死鎖資訊
mysql> show engine innodb status \G
*************************** 1. row ***************************
  Type: InnoDB
  Name: 
Status: 
=====================================
2018-05-10 09:17:10 0x7f1fbc21a700 INNODB MONITOR OUTPUT
=====================================
Per second averages calculated from the last 46 seconds
-----------------
BACKGROUND THREAD
-----------------
srv_master_thread loops: 53 srv_active, 0 srv_shutdown, 240099 srv_idle
srv_master_thread log flush and writes: 0
----------
SEMAPHORES
----------
OS WAIT ARRAY INFO: reservation count 2007
OS WAIT ARRAY INFO: signal count 1987
RW-shared spins 3878, rounds 5594, OS waits 1735
RW-excl spins 3, rounds 91, OS waits 4
RW-sx spins 1, rounds 30, OS waits 1
Spin rounds per wait: 1.44 RW-shared, 30.33 RW-excl, 30.00 RW-sx
------------
TRANSACTIONS
------------
Trx id counter 78405
Purge done for trx's n:o < 78404 undo n:o < 10 state: running but idle
History list length 21
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 421249967052640, not started
0 lock struct(s), heap size 1136, 0 row lock(s)
--------
FILE I/O
--------
I/O thread 0 state: waiting for completed aio requests (insert buffer thread)
I/O thread 1 state: waiting for completed aio requests (log thread)
I/O thread 2 state: waiting for completed aio requests (read thread)
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