How Can I Resolve a SQL Server Race Condition in Order Processing Due to Duplicate Record Retrieval?

Addressing SQL Server Race Conditions in Order Processing

Your order processing system is experiencing race conditions because multiple processors are retrieving the same records. Here's how to fix this:

Understanding the Problem:

The problem stems from the stored procedure's use of a ROWLOCK hint combined with a selection from a separately locked view. This allows multiple processors to lock the same record, leading to data corruption.

Solution Using Hints:

To resolve the race condition, use the READPAST and UPDLOCK hints:

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

SELECT
    OrderID, ProcessorID, etc...
FROM
    OrderTable
WHERE
    ProcessorID = @PROCID</code>

READPAST avoids locked rows during the selection, ensuring continuous query execution. UPDLOCK guarantees proper locking during the update, preventing concurrent modifications.

A More Efficient Solution:

A more streamlined approach uses the OUTPUT clause to combine the SELECT and UPDATE operations:

<code class="language-sql">BEGIN TRAN
    UPDATE TOP (20) foo
    OUTPUT
        OrderID, ProcessorID, etc...
    SET
        ProcessorID = @PROCID
FROM
    foo WITH (ROWLOCK, UPDLOCK, READPAST)
WHERE
    ProcessorID = 0
COMMIT TRAN</code>

This eliminates the need for a separate SELECT statement, improving efficiency and code clarity.

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