What are atomikos transaction logs used for?

Question

I've inherited an application that uses Atomikos for transaction handling in Spring on top of an Oracle database. In production deployments transaction logging has always been enabled by setting com.atomikos.icatch.enable_logging=true but the truth is I can't find any info on what exactly these logs are used for.

The atomikos site states "this should never be disabled on production or data integrity cannot be guaranteed" and I found a comment in a jta.properties on that site that said there is a "risk of losing data after restart or crash" if it is disabled.

We don't enable this in our development environments and are able to use the application normally. I thought they might be used in the case of the application crashing but if so I'm not sure how they'd be used. Maybe automatically during the next startup or manually in some way? In terms of data integrity I know Oracle enables it's own data recovery but maybe these transaction logs hold data that Oracle hasn't seen yet, e.g. if Spring were to crash.

Answer 1

http://fogbugz.atomikos.com/default.asp?community.6.1950.6 seems to indicate that the transaction logs are used for recovery only and can be disabled if you don't need them for recovery.

Answer 2

These logs maintain transaction information in the latest revision that may not be known yet to your database. without this set, recovery after a crash/restart will probably be incorrect.

HTH Guy

Answer 3

Before I answer you question you need to read the begining of this post here How would you tune Distributed ( XA ) transaction for performance? to get the therminology.

The Atomikos is acting as Transaction coordinator who coordinates across the participants which are the different databases. As a coordinator it orchestrate the process of transactions accross the different databases. It is essentialy the same work that a Policemen is doing at the middle of a crossroad.

Atomikos writes its log file in order to know where exactyly in the process of the distributed transaction it is. In case of failure it can trace its uncommited transactions progress and attempt from the place it was previously interrupted. As such the transaction log is very important for the transaction recovery process.