Question

I m looking for a way to continue execution of a transaction despite errors while inserting low-priority data. It seems like real nested transaction could be a solution, but they aren t supported by SQL Server 2005/2008. Another solution would be to have logic to decide if an error is critical or not, but it would seem that s not possible either.

Here s more detail on my scenario:

Data is periodicaly inserted in the database using ADO.NET/C#, and while some of it is vital, some could also be missing without problems. When the inserts are done, some computations are made on the data. (Both vital and non-vital) This whole process is inside a transaction so everything remains in synch.

Currently, transaction save points are used, and partial rollbacks are made on exceptions which occur during non-vital inserts. However, this doesn t work for "batch-abort" errors, which automaticly rollback the entire transaction. I understand some errors are critical, but things like failed casts are considered by SQL Server to be batch-abort errors. (Info on batch errors) I m trying to prevent these errors from bringing down the whole insert if they occur on low priority data.

If what I m describing isn t possible, I m willing to consider any alternative way to achieve data integrity but allow the failure of the non-vital inserts.

Thanks for your help.

Answer 1

Unfortunately, can t be done as you describe (full support for nested transactions would be key here). Couple things I can think of that have been used to get around this in the past:

Best option would probably be to separate the commands into important/non-important commands that could be executed distinctly, naturally this would require that they not be order-dependent on each other
Could also use a messaging based approach (see Service Broker) where you would execute the primary commands inline and push the non-primary commands onto a queue for execution later/separately. The push to the queue would be transactional within the batch, but the execution of the command when you pop off the queue would be separate. This too would require they not be order-dependent on each other.
If order-dependent, you could use the messaging approach for everything, which would ensure order and could have separate messages per operation, then grouping them together (via conversation groups) would allow you to pull them off the queue in order as well and use separate transactions for each type of operation (i.e. primary vs. non-primary). This would require some special coding on your part if all the grouped messages must be a single autonomous operation, but could be done.
I hesitate to even mention this option, because it is a terrible option, but for full disclosure I suppose you could consider it at your discretion if you think it fits (but it is definitely not an architecture that would apply to almost any scenario). You could use xp_cmdshell to call out to the command line and execute sqlcmd/osql for the non-critical tasks - this sqlcmd execution would be in a separate transaction from the module you are executing from, and simply ignoring the xp_cmdshell failure should allow the primary batch to continue.

Those are some ideas...

Answer 2

Can you do your import into a temporary location, using transactions only for the important parts. Once the temp location loaded, having absorbed any non-critical errors, you can copy the data into its final destination in a single transaction. Depends on the nature the work you are doing, but potentially a viable option.

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