TABLOCKX 与可序列化

2021-09-10 00:00:00 sql tsql sql-server

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:

  1. 哪个选项更好?

  1. 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

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