How Can I Prevent Race Conditions When Processing Orders from an SQL Server Queue?

Avoiding Race Conditions in SQL Server Order Queues

Multiple order processors access an order queue via a stored procedure, retrieving 20 orders each. This can cause a race condition where multiple processors grab the same order, resulting in processing errors.

Here's a solution to eliminate this concurrency issue:

One approach uses the READPAST hint to bypass locked rows, coupled with ROWLOCK to prevent lock escalation and UPDLOCK for exclusive row locking. This allows each processor to lock a distinct batch of rows (e.g., processor 1 locks rows 1-20, processor 2 locks rows 21-40, and so on).

The modified stored procedure would look like this:

<code class="language-sql">UPDATE TOP (20) foo
SET ProcessorID = @PROCID
FROM OrderTable foo WITH (ROWLOCK, READPAST, UPDLOCK)
WHERE ProcessorID = 0;</code>

Another method involves using the OUTPUT clause. This combines the SELECT and UPDATE operations into a single atomic statement, guaranteeing immediate availability of the updated rows to the processor. This eliminates the need for separate SELECT and UPDATE operations, thus preventing race conditions.

The above is the detailed content of How Can I Prevent Race Conditions When Processing Orders from an SQL Server Queue?. For more information, please follow other related articles on the PHP Chinese website!