Why Does My SQL Server 2012 Identity Column Skip Increments?

SQL Server 2012 Identity Column Increment Skipping: A Common Issue

SQL Server 2012's auto-incrementing identity columns can exhibit unexpected behavior—sporadic skipping of increments. This disrupts the sequential numbering of records, causing gaps in your table's ID values.

This issue stems from the introduction of sequences in SQL Server 2012. Sequences improve identity generation performance and scalability, but this enhancement can lead to the apparent skipping of increments.

Understanding the Apparent Skipping

When a sequence manages an identity column, it pre-allocates a range of numbers. New records receive values from this range. If the allocated range exceeds the immediate need, it creates the illusion of skipped numbers, even though the underlying sequence is functioning correctly.

Solutions for Maintaining Sequential Increments

To regain the strictly sequential increment behavior of older SQL Server versions, consider these options:

1. Trace Flag 272: Activating trace flag 272 logs every identity value generation. This ensures sequential IDs but may slightly reduce performance.
2. NO CACHE Sequence: Define your sequence with the NO CACHE option. This prevents pre-allocation of large number ranges, guaranteeing sequential assignment.

In Summary

The perceived skipping of identity column increments in SQL Server 2012 is a byproduct of sequence optimization. By understanding this mechanism and using the suggested solutions, you can maintain sequential IDs without sacrificing the performance benefits of sequences.

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