Hi,

I have reviewed the docs and am unsure about the best approach for concurrency issues in my scenario.

I want to track page impressions in a daily log file by incrementing a counter. If the log file for today has not yet been created then the request should create a new log entry and set the counter to 1.

For updates, I could add a verson column to the class but I don't want to actually throw a staleobjectsexception for this use case as I am just incrementing a counter. I could trap the exception and retry the whole transaction by selecting the object again, but I guess this could happen repeatedly and I would need to throw an exception at some point rather than just looping forever!

What about preventing 2 daily log entries being created by 2 requests that both think there isn't one there yet?

Any help with this is really appreciated.

Thanks,

Jason

Regarding preventing two daily entries from being created concurrently, you just need to either a) use the "assigned" id strategy, where you assign the object id yourself, and somehow use the current date to create an object id, or b) create another column to store today's date, and put a unique constraint on it. Either way you will get a unique constraint violation, and you can catch that exception and deal with it.

However, I really think the whole "incrementing a counter" problem is better suited to a direct SQL solution. For example, check out the TableGenerator class in the NH source code.

Thanks for the info. The unique constraint would work well and I can then re-try the whole transaction, updating the new entries instead of trying to insert them.

I did think about using an SQL implementation, possibly using a stored procedure to perform some appropriate locking...or is locking to be avoided at all costs!?