Does SQL Server Identity (Auto-Increment) Continue Incrementing After a Transaction Rollback?

The incremental behavior of SQL Server auto-increment columns after transaction rollback: not a problem

Suppose a .NET transaction inserts data into a SQL Server 2005 database with an auto-incrementing primary key. The Rollback() method correctly rolls back the row insert operation when an error is encountered within the transaction. However, subsequent inserts into the same table increment the auto-increment column as if no rollback occurred, creating a gap in the sequence.

Understand the auto-increment feature

It is important to understand that the design of auto-incrementing numbers is non-transactional. The rationale for this design is that blocking may occur if other transactions must wait to consume or roll back the incremented number before they can continue.

To illustrate this, consider the following scenario where User 1 and User 2 interact with Table A using an auto-increment field as the ID column:

<code>用户 1
------------
begin transaction
insert into A ...
insert into B ...
update C ...
insert into D ...
commit

用户 2
-----------
begin transaction
insert into A ...
insert into B ...
commit</code>

If user 2's transaction happens after user 1's transaction, even just slightly later, their insert operation to table A will be forced to wait for user 1's entire transaction to complete, just to be sure that the first time it came from table A Whether the inserted auto-increment number is used.

Conclusion

Therefore, the behavior of the auto-incrementing column continuing to increment after the transaction is rolled back is not an error, but a deliberately designed strategy. If precise sequential incrementing numbers are required, other mechanisms should be considered for generating such values.

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