Question

我有2个表EXPERIMENT和ENTITIES。 ENTITIES有一个ID字段，该字段引用表EXPERIMENT的主要ID。

我同时与子实体一起插入了多个实验，并陷入了僵局。

show engine innodb status显示调试信息。我无法找到僵局的原因。我猜是因为子实体正在验证实验表中的Foreign_Key而发生的，但这似乎不应该产生死锁。

我正在对ID和SERIALIZABLE事务隔离使用AUTO INCREMENT。

以下是innodb状态下的相关部分：

------------------------
LATEST DETECTED DEADLOCK
------------------------
2019-05-14 12:34:45 0x7000060f3000
*** (1) TRANSACTION:
TRANSACTION 162916, ACTIVE 1 sec inserting
mysql tables in use 1, locked 1
LOCK WAIT 10 lock struct(s), heap size 1136, 6 row lock(s), undo log entries 2
MySQL thread id 183, OS thread handle 123145405919232, query id 2464 localhost 127.0.0.1 root update
INSERT INTO _ENTITIES (TYPE, FK_EXPERIMENT_ID, CONTENT, CREATED_USER_ID) VALUES ('VARIATION', 42, '{"variantName":"Variant 1","actions":[{"blockId":0,"type":"SendEmail","criteria":{"and":[{"operator":"EQ","attr":"_id","val":"Test","ruleId":1,"category":"default"},{"operator":"EQ","attr":"productLanguage","val":"CS_CZ","ruleId":1,"category":"contextual"}]},"order":1,"surfaceActionName":"EMAIL","params":{"verified":true,"selectedTemplate":"Design-Paid-Portfolio-A"},"name":"Action Block 1","treatmentId":"","default":true},{"blockId":1,"type":"wait","criteria":{"and":[{"operator":"EQ","attr":"_id","val":"Test","ruleId":1,"category":"default"},{"operator":"EQ","attr":"productLanguage","val":"CS_CZ","ruleId":1,"category":"contextual"}]},"order":1,"surfaceActionName":"wait","params":{"unit":"hour","data":10,"verified":true},"name":"Action Block 1","treatmentId":"","default":true}],"variantPercentage":80}', 'uk
*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 6728 page no 4 n bits 96 index ENTITIES_EXPERIMENT_ID of table `test_database`.`_entities` trx id 162916 lock_mode X insert intention waiting
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
 0: len 8; hex 73757072656d756d; asc supremum;;

*** (2) TRANSACTION:
TRANSACTION 162906, ACTIVE 1 sec inserting
mysql tables in use 1, locked 1
8 lock struct(s), heap size 1136, 4 row lock(s), undo log entries 2
MySQL thread id 164, OS thread handle 123145403969536, query id 2549 localhost 127.0.0.1 root update
INSERT INTO _ENTITIES (TYPE, FK_EXPERIMENT_ID, CONTENT, CREATED_USER_ID) VALUES ('VARIATION', 33, '{"variantName":"Variant 1","actions":[{"blockId":0,"type":"SendEmail","criteria":{"and":[{"operator":"EQ","attr":"_id","val":"Test","ruleId":1,"category":"default"},{"operator":"EQ","attr":"productLanguage","val":"CS_CZ","ruleId":1,"category":"contextual"}]},"order":1,"surfaceActionName":"EMAIL","params":{"verified":true,"selectedTemplate":"Design-Paid-Portfolio-A"},"name":"Action Block 1","treatmentId":"","default":true},{"blockId":1,"type":"wait","criteria":{"and":[{"operator":"EQ","attr":"_id","val":"Test","ruleId":1,"category":"default"},{"operator":"EQ","attr":"productLanguage","val":"CS_CZ","ruleId":1,"category":"contextual"}]},"order":1,"surfaceActionName":"wait","params":{"unit":"hour","data":10,"verified":true},"name":"Action Block 1","treatmentId":"","default":true}],"variantPercentage":80}', 'uk
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 6728 page no 4 n bits 96 index ENTITIES_EXPERIMENT_ID of table `test_database`.`_entities` trx id 162906 lock mode S
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
 0: len 8; hex 73757072656d756d; asc supremum;;

*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 6728 page no 4 n bits 96 index ENTITIES_EXPERIMENT_ID of table `test_database`.`_entities` trx id 162906 lock_mode X insert intention waiting
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
 0: len 8; hex 73757072656d756d; asc supremum;;

*** WE ROLL BACK TRANSACTION (2)
------------

我应该怎么解释？为什么会发生死锁？

使用的代码是：

Integer generatedId = experimentDAO.add(experimentQO);
......

for..
    entitiesDAO.add(entitiesQO);
....
ExperimentQO experimentQO = experimentDAO.get(generatedId);

添加实体时发生异常。

Answer 1

我看到的是：

Trx＃1正在等待ENTITIES_EXPERIMENT_ID索引上的X模式插入意图锁定（一种间隙锁定）。
Trx＃2持有ENTITIES_EXPERIMENT_ID索引的S锁，这阻止了Trx＃1
Trx＃2也正在等待ENTITIES_EXPERIMENT_ID索引上的插入意图锁定。

我们可以假设Trx＃1还在同一索引上持有S锁。 S锁是共享的，因此多个事务可以同时在同一行（或间隙）上获取S锁。

如果两个事务都先获取了S锁，然后又都尝试请求X锁，那么它们将陷入一种情况，即两者都在等待另一个，而无法打破死锁。

第一步可能是两个INSERT语句都获得了S锁。或者您可能还执行了其他一些查询，这些查询在插入INSERT之前在同一事务中获得了S锁，因此两个事务仍保持各自的S锁。

您尚未显示表定义，因此可能存在一些外键约束，这将导致间接引用的行获得S锁。

MySQL死锁信息调试

1 个答案: