Advice for minimizing locking on an append only table in MS SQL Server?

Question

I'm writing some logging/auditing code that will be running in production (not just when errors are thrown or while developing). After reading Coding Horror's experiences with dead-locking and logging, I decided I should seek advice. (Jeff's solution of "not logging" won't work for me, this is legally mandated security auditing)

Is there an suitable Isolation level for minimizing contention and dead-locking? Any query hints I can add to the insert statement or the stored procedure?

I care deeply about the transactional integrity for everything except the audit table. The idea is that so much will be logged that if a few entries fail, it's not a problem. If the logging stops a some other transaction-- that would be bad.

I can log to a database or a file, although logging to a file is less attractive because I need to be able to display the results somehow. Logging to a file would (almost) guarantee the logging wouldn't interfere with other code though.

Answer 1

A normal transaction (ie. READ COMMITTED) insert already does the 'minimal' locking. Insert intensive applications will not deadlock on the insert, no matter the order of how the insert is mixed with other operations. At worst an intensive insert system may cause page latch contention on the hot spot where insert occurs, but not deadlocks.

To cause deadlocks as described by Jeff there has to be more at play, like any one of the following:

• The system is using a higher isolation level (they had it coming then and well deserve it)
• They were reading from the log table during the transaction (so is no longer 'append-only')
• The deadlock chain involved application layer locks (ie. .Net lock statements in the log4net framework) resulting in undetectable deadlocks (ie. application hangs). Given that solving the problem involved looking at process dumps, I guess this is the scenario they were having.

So as long as you do insert only logging in READ COMMITTED isolation level transactions you are safe. If you expect the same problem I suspect SO had (ie. deadlocks involving application layer locks) then no amount of database wizardry can save you, as the problem can still manifest even if you log on separate transaction or into separate connection.