DBCC CHECKIDENT Atomically Change Identity Seed?

I have a set of staging tables that need to be used to update a hierarchy of tables with foreign keys between them, and identity columns for the primary keys. One way I'm thinking of doing this is to reset the identity seed on the target tables based on the number of rows I have in the staging tables, then to update the staging tables keys to match the vacated range of identity values. I'd insert them with SET IDENTITY_INSERT ON.

The question is: can this be done atomically? It seems that DBCC CHECKIDENT will return the current identity value, but can only change the seed to an absolute value. That would require that I get the current value, add "n" to it, then set the seed value. This would seem to be non-atomic, in that a new row could be inserted between the time I find the "current" value and the time I set the new value.

Does anyone know of a way to pre-allocate a block of identity values atomically? This has to be done in a live OLTB database.

Further research shows that a fundamental assumtion I was maing is incorrect. DBCC CHECKIDENT does not return the current identity seed. I was depending on this to allow me to increment the seed value, but it appears that cannot be done.

It looks like replication might help here, but since this project must be finished by September 1, we don't have time to learn anything else new. It looks like I'll be stuck using cursors and doing these inserts one at a time.

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You can use IDENT_CURRENT() function to return the last used value and IDENT_SEED() to find the created seed.

e.g.

Code Snippet

SELECT TABLE_SCHEMA, TABLE_NAME,
IDENT_SEED(TABLE_SCHEMA + '.' + TABLE_NAME) AS [IDENT_SEED],
IDENT_CURRENT(TABLE_SCHEMA + '.' + TABLE_NAME) AS [IDENT_CURRENT]
FROM INFORMATION_SCHEMA.TABLES
WHERE IDENT_SEED(TABLE_SCHEMA + '.' + TABLE_NAME) IS NOT NULL;

Then use dbcc checkident() to reseed as needed.

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Thanks. This should do it for me. I can check after the DBCC CHECKIDENT to see whether any rows were created within the block that I "reserved", and try again until I get all the values I need.