SQL Server 2008 identity Key auto increment Issue

Question

I recently had to move a database(sql server 2008) to a different server, and I have noticed that in one of the table, the value of identity column has started to get some unexpected values. its set as identity column with identity increment 1 and identity seed 1. After every 10 consecutive entry or so, it would start from another much higher number and increment by 1 for next 10 entries or so and then jump up to another higher number. I can't seem to figure out the issue.

Sorry for the layman language. I am not a DB person.

Answer 1

This is likely not an issue with your identity key but an issue with a framework being used to insert data, or a SP. If you have a stored procedure that inserts data but then is ROLLBACK'd, the ID was reserved but the row is 'deleted'.

So two places to check: One on the frameworks you're using (NHibernate, or Entity Framework, etc?)... those frameworks might be inserting rows then deleting them. Second place to check is INSERT statements in SPROCs and other places you might expect a ROLLBACK.

See: SQL Identity (autonumber) is Incremented Even with a Transaction Rollback

Another issue is that you may just be examining data without sorting it? And when you ported the data you assumed it would be inserted or retrieved always in-ID-order. But because the new table is not 'indexed' the same way you won't necessarily see items in primary-key order. This is less likely if rows appear sequential most of the time with gaps, but worth mentioning.

Answer 2

The following will shed some light on your issue.

1. Create a table with an identity auto increment column
2. Insert 10 rows of random data
3. You will see that the ID values are 1,2,3,4,5,6,7,8,9,10
4. delete from mytable where id=10
5. insert another row into the table
6. now you will see the ID values are 1,2,3,4,5,6,7,8,9,**11**