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我正在使用mysql（innodb作为引擎）的Web应用程序上工作。 我有几个表，包括'用户'，'任务'，'task_histories'。Mysql select ...更新死锁
- '用户' 与属性：id（主键），账号，密码，分数等
- '任务' 与属性：id（主键），得分，USER_ID等
- “task_histories”与属性：id（主键），TASK_ID，USER_ID，取消等
现在我有一个简单的逻辑：如果一个用户完成一个任务，然后我需要添加相应的分数（”任务'）到他的旧分数（'用户'）。所以，我有java代码是这样的：
public class TaskHistoryHandler extends SyncableHandler {
// ignore other methods or fields
// syncableController is a field in superclass and responsible for
// dealing with Mybatis mappers
@Override
public SyncableDO insert(TaskHistoryDO taskhistory, PrincipalDO auth, long taskId) {
taskHistory = syncableController.insert(TaskHistoryDO.class, taskHistory);
if(!taskHistory.isFresh()) {
return taskHistory; // already insert, then return directly
}
if(!taskHistory.isCanceled()) {
TaskDO task = syncableController.getById(TaskDO.class, taskId);
UserMapper userMapper = syncableControlle.getSqlSession().getMapper(UserMapper.class);
UserDO user = userMapper.getUserWithLock(auth.getUserId());
user.setScore(user.getScore() + task.getScore());
userMapper.updateUserScore(user);
}
return taskHistory;
}
}
在另一方面，我有一个基于MyBatis的一个UserMapper类：
public interface UserMapper {
@Select("SELECT * FROM users WHERE id = #{userId} FOR UPDATE")
@ResultMap("user")
UserDO getUserWithLock(@Param("userId") long userId);
@Select("UPDATE users SET score = #{score} WHERE id=#{id}")
int updateUserScore(UserDO user);
}
TaskHistoryHandler的方法是在弹簧控制器处理HTTP请求调用。此外，sqlsession的范围为'WebApplicationContext.SCOPE_REQUEST'，并且在每个http请求之后并且在服务器返回响应之前完成提交。
在本地测试期间没有问题，但服务器上的时间不稳定。该日志如下
org.apache.ibatis.exceptions.PersistenceException:
### Error querying database. Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLTransactionRollbackException: Deadlock found when trying to get lock; try restarting transaction
### The error may exist in im/yon/playtask/model/mapper/UserMapper.java (best guess)
### The error may involve im.yon.playtask.model.mapper.UserMapper.getUserWithLock-Inline
### The error occurred while setting parameters
### SQL: SELECT * FROM users WHERE id = ? FOR UPDATE
### Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLTransactionRollbackException: Deadlock found when trying to get lock; try restarting transaction
这里我的问题是：
- 是什么原因导致的僵局？ （我不知道当两个交易等待对方的锁在我的情况下发布时会发生什么情况）
- 是否可以避免死锁但保证用户的得分与客户端数据库中的得分一致？任何改善代码逻辑的建议？
谢谢！
更新： 这里的InnoDB的状态：
2016-11-23 07:01:40 7f2aa0ac2700
*** (1) TRANSACTION:
TRANSACTION 126179072, ACTIVE 0 sec starting index read
mysql tables in use 1, locked 1
LOCK WAIT 7 lock struct(s), heap size 1184, 3 row lock(s), undo log entries 1
MySQL thread id 4990655, OS thread handle 0x7f2aa1557700, query id 553511517 10.105.39.112 playtask statistics
SELECT * FROM users WHERE id = 41864 FOR UPDATE
*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 53 page no 466 n bits 168 index `PRIMARY` of table `playtask`.`users` trx id 126179072 lock_mode X locks rec but not gap waiting
Record lock, heap no 43 PHYSICAL RECORD: n_fields 18; compact format; info bits 0
0: len 8; hex 800000000000a388; asc ;;
1: len 6; hex 000007855671; asc Vq;;
2: len 7; hex 220000054a1d9d; asc "" J ;;
3: len 5; hex 9999ea055c; asc \;;
4: len 5; hex 999aed705e; asc p^;;
5: len 1; hex 80; asc ;;
6: len 7; hex 73696e61726f75; asc sinarou;;
7: len 30; hex 613732313261356639633664373330623464353536373934306336333730; asc a7212a5f9c6d730b4d5567940c6370; (total 56 bytes);
8: len 16; hex 3934373631393439394071712e636f6d; asc [email protected];;
9: len 4; hex 7fffbf32; asc 2;;
10: len 4; hex 80000000; asc ;;
11: SQL NULL;
12: len 7; hex 73696e61726f75; asc sinarou;;
13: len 4; hex 80000000; asc ;;
14: len 4; hex 80000000; asc ;;
15: len 4; hex 80000000; asc ;;
16: len 4; hex 80000000; asc ;;
17: SQL NULL;
*** (2) TRANSACTION:
TRANSACTION 126179073, ACTIVE 0 sec starting index read
mysql tables in use 1, locked 1
7 lock struct(s), heap size 1184, 3 row lock(s), undo log entries 1
MySQL thread id 4989467, OS thread handle 0x7f2aa0ac2700, query id 553511519 10.105.39.112 playtask statistics
SELECT * FROM users WHERE id = 41864 FOR UPDATE
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 53 page no 466 n bits 168 index `PRIMARY` of table `playtask`.`users` trx id 126179073 lock mode S locks rec but not gap
Record lock, heap no 43 PHYSICAL RECORD: n_fields 18; compact format; info bits 0
0: len 8; hex 800000000000a388; asc ;;
1: len 6; hex 000007855671; asc Vq;;
2: len 7; hex 220000054a1d9d; asc "" J ;;
3: len 5; hex 9999ea055c; asc \;;
4: len 5; hex 999aed705e; asc p^;;
5: len 1; hex 80; asc ;;
6: len 7; hex 73696e61726f75; asc sinarou;;
7: len 30; hex 613732313261356639633664373330623464353536373934306336333730; asc a7212a5f9c6d730b4d5567940c6370; (total 56 bytes);
8: len 16; hex 3934373631393439394071712e636f6d; asc [email protected];;
9: len 4; hex 7fffbf32; asc 2;;
10: len 4; hex 80000000; asc ;;
11: SQL NULL;
12: len 7; hex 73696e61726f75; asc sinarou;;
13: len 4; hex 80000000; asc ;;
14: len 4; hex 80000000; asc ;;
15: len 4; hex 80000000; asc ;;
16: len 4; hex 80000000; asc ;;
17: SQL NULL;
*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 53 page no 466 n bits 168 index `PRIMARY` of table `playtask`.`users` trx id 126179073 lock_mode X locks rec but not gap waiting
Record lock, heap no 43 PHYSICAL RECORD: n_fields 18; compact format; info bits 0
0: len 8; hex 800000000000a388; asc ;;
1: len 6; hex 000007855671; asc Vq;;
2: len 7; hex 220000054a1d9d; asc "" J ;;
3: len 5; hex 9999ea055c; asc \;;
4: len 5; hex 999aed705e; asc p^;;
5: len 1; hex 80; asc ;;
6: len 7; hex 73696e61726f75; asc sinarou;;
7: len 30; hex 613732313261356639633664373330623464353536373934306336333730; asc a7212a5f9c6d730b4d5567940c6370; (total 56 bytes);
8: len 16; hex 3934373631393439394071712e636f6d; asc [email protected];;
9: len 4; hex 7fffbf32; asc 2;;
10: len 4; hex 80000000; asc ;;
11: SQL NULL;
12: len 7; hex 73696e61726f75; asc sinarou;;
13: len 4; hex 80000000; asc ;;
14: len 4; hex 80000000; asc ;;
15: len 4; hex 80000000; asc ;;
16: len 4; hex 80000000; asc ;;
17: SQL NULL;
*** WE ROLL BACK TRANSACTION (2)
向我们展示事务中的所有SQL语句。我期望他们是这样的：'BEGIN; SELECT ... FOR UPDATE; （等等）; COMMIT;' –