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1
TRANSACTION 130718515, ACTIVE 19 sec starting index read
mysql 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 waiting
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) TRANSACTION: #事务2
TRANSACTION 130718516, ACTIVE 14 sec starting index read
mysql tables in use 1, locked 1
4 lock struct(s), heap size 1184, 4 row lock(s), undo log entries 1
MySQL thread id 4, OS thread handle 0x7ffb4993a700, query id 206 localhost root updating
update 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 X
Record 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 waiting
Record 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.log
innodb_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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