问题描述
我有一系列需要以原子方式运行的 T-SQL 查询.(见下文)...目的是允许 1 个用户一次检索一个唯一的行,并防止其他用户同时检索同一行.
I have a series of T-SQL queries that I need to run atomically. (See Below)... The purpose is to allow 1 user to retrieve a single, unique row at a time and prevent other users from retrieving the same row simultaneously.
到目前为止,我已经看到了两种可能的解决方案.1) 表提示 (HOLDLOCK, TABLOCKX) 和 2) 事务隔离级别 (SERIALIZABLE)...
So far I have seen two possible solutions. 1) Table Hints (HOLDLOCK, TABLOCKX) and 2) Transaction Isolation Level (SERIALIZABLE)...
我的问题:
哪个选项更好?
Which option is better?
还有其他/更好的解决方案吗?
Is there another/better solution?
DECLARE @recordId int; SELECT @recordId = MIN([id]) FROM Exceptions WHERE [status] = 'READY'; UPDATE Exceptions SET [status] = 'PROCESSING', [username] = @Username WHERE [id] = @recordId; SELECT * FROM Exceptions WHERE [id] = @recordId;
推荐答案
在这种情况下,
- HOLDLOCK = SERIALIZABLE = 持续时间,并发
- TABLOCKX = 独占表锁
这两个概念是不同的,你想要的也不是.
The 2 concepts are different and neither does what you want.
做你想做的事,避免竞争条件,需要强制一个非阻塞(READPAST)排他(UPDLOCK)行级(ROWLOCK)锁,.您还可以使用 OUTPUT 子句使其成为具有原子性的单个语句.这可以很好地扩展.
To do what you want, to avoid race conditions, you need to force a non-blocking (READPAST) exclusive (UPDLOCK) row level (ROWLOCK) lock,. You can also use the OUTPUT clause to make it a single statement that will be atomic. This scales well.
UPDATE E SET [status] = 'PROCESSING', [username] = @Username OUTPUT INSERTED.* FROM ( SELECT TOP 1 id, [status], [username] FROM Exceptions (ROWLOCK, READPAST, UPDLOCK) WHERE [status] = 'READY' ORDER BY id ) E
总的来说,锁有3个方面
In general, locks have 3 aspects
- 粒度 = 锁定的内容 = 行、页、表(PAGLOCK、ROWLOCK、TABLOCK)
- 隔离级别 = 锁定持续时间、并发性(HOLDLOCK、READCOMMITTED、REPEATABLEREAD、SERIALIZABLE)
- 模式 = 共享/排他性 (UPDLOCK, XLOCK)
和
- 组合"例如 NOLOCK, TABLOCKX