Sql-server – Raise error from Stored PROC in SQL Server PDW

We recently had this discussion at my workplace.

First, I want to commend you for doing the "right thing" by using HASHBYTES() over CHECKSUM() to detect changes. Microsoft specifically cautions against using CHECKSUM(@input) for this purpose as its collision rate is very high compared to that of HASHBYTES('SHA1', @input). One advantage CHECKSUM() does have, though, is that there is no (obvious) restriction on the size of its input.

Second, if you use HASHBYTES() I recommend using SHA1 as your hash algorithm. Of the available options SHA1 has the lowest collision rate, and speed is not a concern for your use case.

Finally, To use HASHBYTES() against inputs larger than 8000 bytes you'll have to:

1. Split your input into 8000 byte chunks.
2. Hash each chunk.

3. Somehow combine the resulting hashes and hash them to get your final output.

   You can do this in one of two ways:

   1. Convert your hash outputs into strings, concatenate them, and hash the result.
   2. Stick all your hash outputs into a memory table and take their aggregate checksum using CHECKSUM_AGG().

4. Encapsulate this work as a function that takes NVARCHAR(MAX) as its input.

All that said, it is all-around simpler to just compare the proc definitions directly using OBJECT_DEFINITION() as gbn suggested, or to simply push all definitions out everywhere as often as you like, as Mike suggested.

I wonder what kind of environment would significantly benefit from a process that deployed only changed procedures and used hashes to avoid copying around and comparing full definitions. You'd need to have a lot of procedures to keep in sync.

Error handling should be (IMO) for the whole stored procedure: so loop inside the TRY/CATCH

Not least, what happens when more code is added pre- or post-loop?
Then you need the TRY/CATCH to cover both loop and new code.

Poor maintainability and extra work required.

You can have an inner TRY/CATCH if you want to handle certain inner errors: this is acceptable for, say, "UPSERT" calls (before SQL Server 2008 MERGE of course). See Pros and Cons of Checking if value exist for unique column or let db raise unique error on inserting for more