Question

Is there a good C++ framework to implement XA distributed transactions?

With the term ‘good’ I mean usable, simple (doesn’t imply ‘easy’), well-structured.

Due to study reasons, at the moment I’m proceeding with a personal implementation, following X/Open XA specification.

Thank you in advance.

Answer 1

I am not aware of an open-source or free transaction monitor that has any degree of maturity, although This link does have some fan-out. The incumbent commercial ones are BEA’s Tuxedo, Tibco’s Enterprise Message Service (really a transactional message queue manager like IBM’s MQ) and Transarc’s Encina (now owned by IBM). These systems are all very expensive.

If you want to make your own (and incidentally make a bit of a name for yourself by filling a void in the open-source software space) get a copy of Grey and Reuter. This is the definitive work on transaction processing systems architecture, written by two of the foremost experts in the field.

Interestingly, they claim that one can implement a working TP monitor in around 10,000 lines of C. This actually sounds quite reasonable, as what it does is not all that complex. On occasion I have been tempted to try.

Essentially you need to make a distributed transaction coordinator that runs as a daemon process. You will need to get the resource manager protocol working from it, so starting with this as a prototype is probably a good start. If you can get it to independently roll back or commit a transaction you have the basis of the TM-RM interface.

The XA API as defined in the spec is the API to control the transaction manager. Strictly speaking, you don’t need to make a 3-tier architecture to use distributed transactions of this sort, but they are more or less pointless without a TP monitor. How you communicate from the front-end to the middle-tier can be left as an exercise for the reader. You are probably best off using an existing ORB, of which there are several good open-source implementations available.

Depending on whether you want to make the DTC and the app server separate processes (which is possibly desirable for stability but not strictly necessary) you could also use ACE as a basis for the DTC server.

If you want to make a high-performance middle-tier server, check out Douglas Schmidt’s ACE framework. This comes with an ORB called TAO, and is flexible enough to allow you to use more or less any threading model that takes your fancy. Using this is a trade-off between learning it and the effort of writing your own and debugging all the synchronisation and concurrancy issues.