How Can I Efficiently Process an SQL Server Queue with Concurrent Clients?

Concurrent Client Processing of an SQL Server Queue

Consider a scenario where multiple clients concurrently execute tasks from a queue represented by a table in SQL Server. The challenge arises when simultaneous queries attempt to lock the same row.

To address this, the article recommends the OUTPUT clause introduced in SQL Server 2005. This allows for dequeuing operations to be executed atomically, skipping any locked rows:

with CTE as (
      SELECT TOP(1) COMMAND, PROCESSED
      FROM TABLE WITH (READPAST)
      WHERE PROCESSED = 0)
    UPDATE CTE
      SET PROCESSED = 1
      OUTPUT INSERTED.*;

Additionally, structuring the table with the leftmost clustered index key on the PROCESSED column and avoiding secondary non-clustered indexes is crucial for optimal performance in concurrent operations.

Furthermore, to maintain integrity, it's emphasized that the table should primarily serve as a queue, avoiding other usage scenarios that could lead to potential deadlocks and performance degradation.

By adhering to these recommendations, you can achieve high-throughput concurrent processing of tasks using SQL Server as a queueing mechanism.

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