How Can I Achieve SELECT FOR UPDATE Functionality in SQL Server?

Getting Exclusive Row Access with SQL Server: Exploring SELECT FOR UPDATE

The concept of SELECT FOR UPDATE is well-known in Oracle, DB2, and MySQL, allowing developers to acquire exclusive locks on rows while retrieving data, preventing other concurrent transactions from modifying the selected data. However, when it comes to using SELECT FOR UPDATE with SQL Server, there are some notable differences.

In the provided code, the attempt to use WITH (updlock) to achieve row-level locking did not yield the desired result, as it also blocked other connections from selecting different rows. To address this, let's explore various options for SELECT FOR UPDATE in SQL Server:

ROWLOCK

The ROWLOCK hint can be used to set row-level locking, but it locks the entire row, even for SELECT operations on different rows. This behavior matches the same row scenario, but not the different row scenario.

updlock, rowlock

Combining updlock and rowlock does not improve the situation; it still results in blocking for both same and different row SELECTs.

xlock,rowlock

Like updlock,rowlock, this combination provides broad locking, affecting both same and different row selections.

repeatableread

Repeatableread is an isolation level that prevents data manipulation anomalies like phantom reads. However, it does not perform row-level locking, offering no solution for this requirement.

DBCC TRACEON (1211,-1)

This trace flag sets a database-wide ROWLOCK for all read operations, effectively simulating row-level locking. However, it affects all connections and may not be appropriate in all scenarios.

rowlock,xlock,holdlock

This combination also locks the entire row for SELECTs, including those on different rows.

updlock,holdlock

Similar to rowlock,xlock,holdlock, this combination provides row-level locking but extends it to include HOLDLOCK semantics.

UPDLOCK,READPAST

For snapshot isolation level, this combination allows SELECT without row locks for committable reads. However, it does not provide exclusive locks and may not be suitable for this use case.

Conclusion

Regrettably, none of the explored options provide the exact behavior of SELECT FOR UPDATE as known in other DBMSs with SQL Server. While row-level locking is an option via ROWLOCK, it also affects other SELECT operations, which may not be desirable. In such cases, catching deadlocks and snapshot concurrency issues may be a necessary alternative to achieve the desired level of data consistency.

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