正常情况下，死锁发生时，权重最小的连接将被kill并回滚。但是为了找出语句来优化，启用可启用死锁将死锁信息记录下来。

#step 1：窗口一mysql> start transaction;mysql> update aa set name='aaa' where id = 1; #step 2：窗口二mysql> start transaction;mysql> update bb set name='bbb' where id = 1; #step 3：窗口一mysql> update bb set name='bbb';#step 4：窗口三#是否自动提交mysql> show variables like 'autocommit';+---------------+-------+| Variable_name | Value |+---------------+-------+| autocommit | ON |+---------------+-------+ #查看当前连接mysql> show processlist;mysql> show full processlist;mysql> SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST;+----+------+-----------+------+---------+------+-------+------------------+| Id | User | Host | db | Command | Time | State | Info |+----+------+-----------+------+---------+------+-------+------------------+| 4 | root | localhost | test | Sleep | 244 | | NULL || 5 | root | localhost | test | Sleep | 111 | | NULL || 6 | root | localhost | NULL | Query | 0 | init | show processlist |+----+------+-----------+------+---------+------+-------+------------------+ #查看当前正在被锁的事务（锁请求超时后则查不到）mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_LOCKS;+------------------+-------------+-----------+-----------+-------------+-----------------+------------+-----------+----------+----------------+| lock_id | lock_trx_id | lock_mode | lock_type | lock_table | lock_index | lock_space | lock_page | lock_rec | lock_data |+------------------+-------------+-----------+-----------+-------------+-----------------+------------+-----------+----------+----------------+| 130718495:65:3:4 | 130718495 | X | RECORD | `test`.`bb` | GEN_CLUST_INDEX | 65 | 3 | 4 | 0x000000000300 || 130718496:65:3:4 | 130718496 | X | RECORD | `test`.`bb` | GEN_CLUST_INDEX | 65 | 3 | 4 | 0x000000000300 |+------------------+-------------+-----------+-----------+-------------+-----------------+------------+-----------+----------+----------------+ #查看当前等待锁的事务（锁请求超时后则查不到）mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_LOCK_WAITS; +-------------------+-------------------+-----------------+------------------+| requesting_trx_id | requested_lock_id | blocking_trx_id | blocking_lock_id |+-------------------+-------------------+-----------------+------------------+| 130718499 | 130718499:65:3:4 | 130718500 | 130718500:65:3:4 |+-------------------+-------------------+-----------------+------------------+ #查看当前未提交的事务（如果死锁等待超时,事务可能还没有关闭）mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_TRX;+--------------------------------------------------------------------------------------------------------+| trx_id | trx_state | trx_started | trx_requested_lock_id | trx_wait_started | trx_weight |+-----------+-----------+---------------------+-----------------------+---------------------+------------+| 130718500 | RUNNING | 2018-03-12 09:28:10 | NULL | NULL | 3 || 130718499 | LOCK WAIT | 2018-03-12 09:27:59 | 130718499:65:3:4 | 2018-03-12 09:32:48 | 5 |==========================================================================================================| trx_mysql_thread_id | trx_query | trx_operation_state | trx_tables_in_use |+---------------------+---------------------------------------+---------------------+-------------------+| 4 | NULL | NULL | 0 || 5 | update bb set name='bbb' | starting index read | 1 |=========================================================================================================| trx_tables_locked | trx_lock_structs | trx_lock_memory_bytes | trx_rows_locked | trx_rows_modified |+-------------------+------------------+-----------------------+-----------------+-------------------+| 0 | 2 | 360 | 3 | 1 || 1 | 4 | 1184 | 4 | 1 |===========================================================================================================================| trx_concurrency_tickets | trx_isolation_level | trx_unique_checks | trx_foreign_key_checks | trx_last_foreign_key_error |+-------------------------+---------------------+-------------------+------------------------+----------------------------+| 0 | REPEATABLE READ | 1 | 1 | NULL || 0 | REPEATABLE READ | 1 | 1 | NULL |===========================================================================================================================| trx_adaptive_hash_latched | trx_adaptive_hash_timeout | trx_is_read_only | trx_autocommit_non_locking |+---------------------------+---------------------------+------------------+----------------------------+| 0 | 10000 | 0 | 0 || 0 | 10000 | 0 | 0 |+---------------------------+---------------------------+------------------+----------------------------+ #查看正在被访问的表mysql> show OPEN TABLES where In_use > 0;+----------+-------+--------+-------------+| Database | Table | In_use | Name_locked |+----------+-------+--------+-------------+| test | bb | 1 | 0 |+----------+-------+--------+-------------+#step 3：窗口一 （若第三步中锁请求太久，则出现锁超时而终止执行）mysql> update bb set name='bbb';ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction #"窗口一" 锁请求超时前，执行第五步，使死锁产生，则该连接 "窗口二" 执行终止，"窗口一" 顺利执行#step 5：窗口二mysql> update aa set name='aa';ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction

查看最近一个死锁情况

#查看最近一个死锁情况mysql> SHOW ENGINE INNODB STATUS\G ;...............------------------------LATEST DETECTED DEADLOCK------------------------2018-03-12 11:01:06 7ffb4993a700 #发生时间*** (1) TRANSACTION: #事务1TRANSACTION 130718515, ACTIVE 19 sec starting index readmysql tables in use 1, locked 1 #正被访问的表LOCK WAIT 4 lock struct(s), heap size 1184, 4 row lock(s), undo log entries 1 #影响行数MySQL thread id 5, OS thread handle 0x7ffb498f8700, query id 205 localhost root updating #线程/连接host/用户update bb set name='bb' #请求语句*** (1) WAITING FOR THIS LOCK TO BE GRANTED: #等待以下资源 （锁定位置及锁模式）RECORD LOCKS space id 65 page no 3 n bits 72 index `GEN_CLUST_INDEX` of table `test`.`bb` trx id 130718515 lock_mode X waitingRecord lock, heap no 5 PHYSICAL RECORD: n_fields 5; compact format; info bits 0 0: len 6; hex 000000000300; asc ;; 1: len 6; hex 000007ca9b34; asc 4;; 2: len 7; hex 1f000002092075; asc u;; 3: len 4; hex 80000001; asc ;; 4: len 2; hex 6262; asc bb;; *** (2) TRANSACTION: #事务2TRANSACTION 130718516, ACTIVE 14 sec starting index readmysql tables in use 1, locked 14 lock struct(s), heap size 1184, 4 row lock(s), undo log entries 1MySQL thread id 4, OS thread handle 0x7ffb4993a700, query id 206 localhost root updatingupdate aa set name='aa' #请求语句*** (2) HOLDS THE LOCK(S): #持有锁资源RECORD LOCKS space id 65 page no 3 n bits 72 index `GEN_CLUST_INDEX` of table `test`.`bb` trx id 130718516 lock_mode XRecord lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0 0: len 8; hex 73757072656d756d; asc supremum;; Record lock, heap no 3 PHYSICAL RECORD: n_fields 5; compact format; info bits 0 0: len 6; hex 000000000301; asc ;; 1: len 6; hex 000007ca9b17; asc ;; 2: len 7; hex 9000000144011e; asc D ;; 3: len 4; hex 80000002; asc ;; 4: len 2; hex 6262; asc bb;; Record lock, heap no 5 PHYSICAL RECORD: n_fields 5; compact format; info bits 0 0: len 6; hex 000000000300; asc ;; 1: len 6; hex 000007ca9b34; asc 4;; 2: len 7; hex 1f000002092075; asc u;; 3: len 4; hex 80000001; asc ;; 4: len 2; hex 6262; asc bb;; *** (2) WAITING FOR THIS LOCK TO BE GRANTED:RECORD LOCKS space id 64 page no 3 n bits 80 index `GEN_CLUST_INDEX` of table `test`.`aa` trx id 130718516 lock_mode X waitingRecord lock, heap no 7 PHYSICAL RECORD: n_fields 5; compact format; info bits 0 0: len 6; hex 000000000200; asc ;; 1: len 6; hex 000007ca9b33; asc 3;; 2: len 7; hex 1e000001d53057; asc 0W;; 3: len 4; hex 80000001; asc ;; 4: len 2; hex 6161; asc aa;; *** WE ROLL BACK TRANSACTION (2)...............#死锁记录只记录最近一个死锁信息，若要将每个死锁信息都保存到错误日志，启用以下参数：mysql> show variables like 'innodb_print_all_deadlocks';+----------------------------+-------+| Variable_name | Value |+----------------------------+-------+| innodb_print_all_deadlocks | OFF |+----------------------------+-------+ #上面 【step 3：窗口一】若一直请求不到资源，默认50秒则出现锁等待超时。mysql> show variables like 'innodb_lock_wait_timeout'; +--------------------------+-------+| Variable_name | Value |+--------------------------+-------+| innodb_lock_wait_timeout | 50 |+--------------------------+-------+ ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction #设置全局变量 锁等待超时为60秒（新的连接生效）#mysql> set session innodb_lock_wait_timeout=50; mysql> set global innodb_lock_wait_timeout=60; #上面测试中，当事务中的某个语句超时只回滚该语句，事务的完整性属于被破坏了。为了回滚这个事务，启用以下参数：mysql> show variables like 'innodb_rollback_on_timeout';+----------------------------+-------+| Variable_name | Value |+----------------------------+-------+| innodb_rollback_on_timeout | OFF |+----------------------------+-------+

最终参数设置如下：(重启服务重新连接测试)

[mysqld]log-error =/var/log/mysqld3306.loginnodb_lock_wait_timeout=60 #锁请求超时时间(秒)innodb_rollback_on_timeout = 1 #事务中某个语句锁请求超时将回滚真个事务innodb_print_all_deadlocks = 1 #死锁都保存到错误日志#若手动删除堵塞会话，删除 Command='Sleep' 、无State、无Info、trx_weight 权重最小的。show processlist;SELECT trx_mysql_thread_id,trx_state,trx_started,trx_weight FROM INFORMATION_SCHEMA.INNODB_TRX;

总结

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