我有下表
CREATE TABLE IF NOT EXISTS `task` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`job_id` int(10) unsigned NOT NULL COMMENT 'The id of the related job',
`server_id` tinyint(4) NOT NULL DEFAULT '0' COMMENT 'job/task owner',
`jobtype_id` int(10) unsigned NOT NULL DEFAULT '0',
`node_id` int(10) unsigned NOT NULL COMMENT 'The id of the user currently executing this task',
`status` enum('QUEUED','EXECUTING','COMPLETED','CANCELED','TERMINATED','PAUSED','FAILED') NOT NULL COMMENT 'Current status of the task',
`last_updated` int(11) NOT NULL COMMENT 'When was the last status change of this task. Used in requeueing hung tasks',
`data_in` blob NOT NULL COMMENT 'An input data to the task. Sets when the task is created.',
`data_out` blob NOT NULL COMMENT 'An output data of the task. Sets upon task completion. Can be absent.',
`speed` bigint(20) unsigned NOT NULL DEFAULT '0',
`time_spent` int(11) NOT NULL DEFAULT '0',
`has_data_out` tinyint(1) NOT NULL COMMENT 'Shows if the task has any output data. Serves caching purposes. Used by Summarizers to quickly find out what tasks of the job yielded data.',
`comment` varchar(200) NOT NULL DEFAULT '',
PRIMARY KEY (`id`),
KEY `fk_task_job_id` (`job_id`),
KEY `index_has_data_out` (`has_data_out`),
KEY `index_last_updated` (`last_updated`),
KEY `index_status` (`status`),
KEY `fk_task_userid` (`node_id`),
KEY `jobtype_id` (`jobtype_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='This table holds all subjobs - tasks' AUTO_INCREMENT=1081595 ;
--
-- Constraints for dumped tables
--
--
-- Constraints for table `task`
--
ALTER TABLE `task`
ADD CONSTRAINT `task_ibfk_5` FOREIGN KEY (`job_id`) REFERENCES `job` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
ADD CONSTRAINT `task_ibfk_7` FOREIGN KEY (`jobtype_id`) REFERENCES `jobtype` (`id`),
ADD CONSTRAINT `task_ibfk_8` FOREIGN KEY (`node_id`) REFERENCES `node` (`id`);
以及下面的死锁问题：
------------------------
LATEST DETECTED DEADLOCK
------------------------
110831 14:23:56
*** (1) TRANSACTION:
TRANSACTION 102B4D2, ACTIVE 0 sec, OS thread id 5480
mysql tables in use 2, locked 1
LOCK WAIT 7 lock struct(s), heap size 1248, 4 row lock(s), undo log entries 3
MySQL thread id 74315, query id 2364347 192.168.1.120 usr_sl3 Sending data
select `usr_sl3`.`task`.`id` from `usr_sl3`.`task` where (`usr_sl3`.`task`.`node_id` = 103 and `usr_sl3`.`task`.`status` = 'EXECUTING') for update
*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 38 page no 2303 n bits 576 index `index_status` of table `usr_sl3`.`task` trx id 102B4D2 lock_mode X locks rec but not gap waiting
Record lock, heap no 471 PHYSICAL RECORD: n_fields 2; compact format; info bits 32
0: len 1; hex 02; asc ;;
1: len 4; hex 00107dac; asc } ;;
*** (2) TRANSACTION:
TRANSACTION 102B4D3, ACTIVE 0 sec, OS thread id 5692 starting index read, thread declared inside InnoDB 500
mysql tables in use 2, locked 1
7 lock struct(s), heap size 1248, 4 row lock(s), undo log entries 3
MySQL thread id 74354, query id 2364348 192.168.1.120 usr_sl3 Sending data
select `usr_sl3`.`task`.`id` from `usr_sl3`.`task` where (`usr_sl3`.`task`.`node_id` = 95 and `usr_sl3`.`task`.`status` = 'EXECUTING') for update
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 38 page no 2303 n bits 576 index `index_status` of table `usr_sl3`.`task` trx id 102B4D3 lock_mode X locks rec but not gap
Record lock, heap no 471 PHYSICAL RECORD: n_fields 2; compact format; info bits 32
0: len 1; hex 02; asc ;;
1: len 4; hex 00107dac; asc } ;;
*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 38 page no 2303 n bits 576 index `index_status` of table `usr_sl3`.`task` trx id 102B4D3 lock_mode X locks rec but not gap waiting
Record lock, heap no 481 PHYSICAL RECORD: n_fields 2; compact format; info bits 32
0: len 1; hex 02; asc ;;
1: len 4; hex 00107dab; asc } ;;
*** WE ROLL BACK TRANSACTION (2)
您能帮我理解这个僵局的机制吗？
这两个查询是从不同的线程发出的。每个线程在查询中都有自己的node_id。没有两个查询具有相同的node_id。
我怀疑，我可以通过在字段（node_id，status）上创建复合索引来解决这种情况，但这不是一个好的解决方案，我认为。我需要了解问题的本质。
同一查询上的这些死锁会定期发生，而不是一次或两次。
对受影响的查询进行 EXPLAIN 给出了有趣的结果：
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE task index_merge index_status,fk_task_userid index_status,fk_task_userid 1,4 NULL 1 Using intersect(index_status,fk_task_userid); Using where; Using index
MySQL版本是5.5。
此外，在死锁发生时，表不包含与受影响查询的条件匹配的行（例如 selectusr_sl3.task.id from usr_sl3.task where (usr_sl3.task.node_id= 95 和usr_sl3.task.status= '执行') 进行更新
根本不产生任何行）。
提前致谢。
