线上某个库发生死锁，如下：
1. ------------------------
LATEST DETECTED DEADLOCK
------------------------
140417 11:45:12
*** (1) TRANSACTION:
TRANSACTION 216AA52F, ACTIVE 0 sec updating or deleting
mysql tables in use 1, locked 1
LOCK WAIT 4 lock struct(s), heap size 1248, 3 row lock(s), undo log entries 4
MySQL thread id 6240192, OS thread handle 0x2b53a11c2700, query id 671755133 10.97.51.53 gds_fare update
REPLACE INTO gds_policy_binding_07 ( dep_city, arr_city, agent_id, fare_type, fare_id, binding_status, order_num, gmt_create, gmt_modified ) VALUES ( 'WUH', 'WNZ', 1553, 1, 81431003, 1, 0, NOW(), NOW() ) , ( 'WUH', 'WNZ', 1553, 1, 81431004, 1, 0, NOW(), NOW() ) , ( 'WUH', 'WNZ', 1553, 1, 83832489, 1, 0, NOW(), NOW() ) , ( 'WUH', 'WNZ', 1553, 1, 83836367, 1, 0, NOW(), NOW() ) , ( 'WUH', 'WNZ', 1553, 1, 81431005, 1, 0, NOW(), NOW() ) , ( 'WUH', 'WNZ', 1553, 1, 83832485, 1, 0, NOW(), NOW() ) , ( 'WUH', 'WNZ', 1553, 1, 81431006, 1, 0, NOW(), NOW() )
*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 789 page no 11573 n bits 496 index `policy_binding_unique` of table `gds_fare`.`gds_policy_binding_07` trx id 216AA52F lock_mode X waiting
*** (2) TRANSACTION:
TRANSACTION 216AA530, ACTIVE 0 sec updating or deleting, thread declared inside InnoDB 494
mysql tables in use 1, locked 1
5 lock struct(s), heap size 1248, 7 row lock(s), undo log entries 5
MySQL thread id 6240166, OS thread handle 0x2b537ddaf700, query id 671755135 10.97.24.28 gds_fare update
REPLACE INTO gds_policy_binding_07 ( dep_city, arr_city, agent_id, fare_type, fare_id, binding_status, order_num, gmt_create, gmt_modified ) VALUES ( 'WUH', 'WNZ', 1553, 1, 81429153, 1, 0, NOW(), NOW() ) , ( 'WUH', 'WNZ', 1553, 1, 83832490, 1, 0, NOW(), NOW() ) , ( 'WUH', 'WNZ', 1553, 1, 83832487, 1, 0, NOW(), NOW() ) , ( 'WUH', 'WNZ', 1553, 1, 83832478, 1, 0, NOW(), NOW() ) , ( 'WUH', 'WNZ', 1553, 1, 81429154, 1, 0, NOW(), NOW() ) , ( 'WUH', 'WNZ', 1553, 1, 81431004, 1, 0, NOW(), NOW() )
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 789 page no 11573 n bits 496 index `policy_binding_unique` of table `gds_fare`.`gds_policy_binding_07` trx id 216AA530 lock_mode X
*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 789 page no 11573 n bits 496 index `policy_binding_unique` of table `gds_fare`.`gds_policy_binding_07` trx id 216AA530 lock_mode X waiting
*** WE ROLL BACK TRANSACTION (1)
问题是应用断在并发执行该replace语句的时候会发生死锁，死锁的原因是唯一建冲突了。
但是单条DML语句怎么会发生死锁呢？？？
参照mysql ref ，执行replace语句时， 如果旧行和新行（要插入的数据）主键或者唯一健冲突的话，replace语句相当于2条sql：1. delete 就行;2. insert新数据; （如果想验证，可以在表上建insert，delete的触发器来测试，会发现replace语句会触发insert和delete的触发器执行）
REPLACE works exactly like INSERT, except that if an old row in the table has the same value as a new row for aPRIMARY KEY or a UNIQUE index, the old row is deleted before the new row is inserted. See Section 13.2.5, “INSERT Syntax”.
参见： http://dev.mysql.com/doc/refman/5.5/en/replace.html
http://dev.mysql.com/doc/refman/5.5/en/insert.html
所以发生死锁的原因就明朗了，那么解决的方法就是用insert ... on duplicate key update...语句来替换replace语句，问题的到解决。
但是insert ... on duplicate key update语句的性能比replace稍微差一点。