Why Do SQL Server Identity Columns Increment Even After Transaction Rollbacks?

Understanding SQL Server Identity Column Behavior During Rollbacks

SQL Server's auto-incrementing identity columns present a unique characteristic: they continue to increment even after a transaction rollback. This can result in gaps within the identity sequence, a potential issue in specific applications.

When an INSERT statement within a transaction fails and the transaction is rolled back, the inserted rows are removed. However, the identity value assigned before the rollback remains unchanged. This leads to unused identity values, creating gaps or potentially causing issues if you attempt to re-use these values.

This non-transactional nature of identity columns is intentional. In a multi-user environment, making identity assignment transactional would introduce significant performance overhead and bottlenecks, as it would require locking mechanisms to prevent concurrent access and allocation of the same identity value.

Consequently, recovering the "lost" identity values after a rollback isn't possible.

To mitigate identity gaps, consider alternative approaches for generating unique identifiers, including:

• GUIDs (Globally Unique Identifiers): Provide universally unique values, eliminating the possibility of duplicates.
• Sequences (SQL Server 2012 and later): Offer a more controlled and efficient mechanism for generating unique numbers.
• Custom Logic: Develop application-level logic to generate unique identifiers outside the database, providing greater control over the generation process.

The above is the detailed content of Why Do SQL Server Identity Columns Increment Even After Transaction Rollbacks?. For more information, please follow other related articles on the PHP Chinese website!