我有一个存储过程,它选择 1 条记录。可以从不同 PC 上的多个不同应用程序调用存储过程。思路是存储过程带回下一条需要处理的记录,如果两个应用程序同时调用存储过程,不应该带回相同的记录。我的查询如下,我正在尝试尽可能高效地编写查询(sql 2008)。它能比这更有效吗?
CREATE PROCEDURE GetNextUnprocessedRecord
AS
BEGIN
SET NOCOUNT ON;
--ID of record we want to select back
DECLARE @iID BIGINT
-- Find the next processable record, and mark it as dispatched
-- Must be done in a transaction to ensure no other query can get
-- this record between the read and update
BEGIN TRAN
SELECT TOP 1
@iID = [ID]
FROM
--Don't read locked records, only lock the specific record
[MyRecords] WITH (READPAST, ROWLOCK)
WHERE
[Dispatched] is null
ORDER BY
[Received]
--Mark record as picked up for processing
UPDATE
[MyRecords]
SET
[Dispatched] = GETDATE()
WHERE
[ID] = @iID
COMMIT TRAN
--Select back the specific record
SELECT
[ID],
[Data]
FROM
[MyRecords] WITH (NOLOCK, READPAST)
WHERE
[ID] = @iID
END
最佳答案
使用 READPAST 锁定提示是正确的,并且您的 SQL 看起来不错。
我会添加 use XLOCK 虽然它也是 HOLDLOCK/SERIALIZABLE
...
[MyRecords] WITH (READPAST, ROWLOCK, XLOCK)
...
这意味着您获得 ID,并在继续和更新它时独占锁定该行。
编辑:在 Dispatched 和 Received 列上添加索引以使其更快。如果 [ID](我假设它是 PK)没有聚集,则包括 [ID]。并过滤索引,因为它是 SQL 2008
您也可以使用这种结构,无需 XLOCK 或 HOLDLOCK 即可一次性完成所有操作
UPDATE
MyRecords
SET
--record the row ID
@id = [ID],
--flag doing stuff
[Dispatched] = GETDATE()
WHERE
[ID] = (SELECT TOP 1 [ID] FROM MyRecords WITH (ROWLOCK, READPAST) WHERE Dispatched IS NULL ORDER BY Received)
UPDATE, assign, set in one
关于sql-server - 高效事务,记录锁定,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/574549/