Dear all, I'm the author of LIXA project (http://lixa.sourceforge.net/) and I would discuss a little about "two phase commit" transactions for PHP applications. "Two phase commit" means I can write a program that uses two (or more) Resource Managers (for example databases, like MySQL and PostgreSQL) with ACID transactions that span all the databases. With two phase commit I can perform a *global* commit that commits the changes inside two or more databases at the *same* *time*. This is quite different than performing two (or more) distinct commits: with distinct commits it may happen the first one completes and the second one catches an error.
LIXA project implements two X/Open standards: "XA specification" and "TX (transaction demarcation) specification". XA describes an interface between the Resource Managers (databases) and the Transaction Manager (for example LIXA); TX describes an interface between the Application Program (your own custom software) and the Transaction Manager (for example LIXA). The "TX (transaction demarcation) specification" is a C API very easy to understand and use when you are developing a C (or C++) software. When I started developing LIXA, I figured out it would have been straightforward to wrap it for other languages like PHP, Perl, Python, Ruby and so on... Unfortunately I discovered it's not easy to extend the TX API to other languages: creating a wrapper for TX API is trivial because it's just the matter of SWIG (http://www.swig.org/) hacking. Integrating the TX wrapped interface with *the* *environment* is a completely different task. These are the issues I partially solved integrating LIXA with PHP. 1. XA interface is a C level interface: the PHP database drivers must be changed at C source level to avoid many leaps between C and PHP code. The most important PHP database drivers are distributed with PHP core itself => patching their source code is equivalent to patch PHP core. 2. As a consequence of the first point, the LIXA PHP wrapper itself should be distributed with PHP core to avoid dependencies between some core extensions and an external extension. 3. The TX API does not deal with the concept of "connection" because it's implicit: every process/thread has its own connection with every Resource Manager (database). Better explained: tx_open(), tx_begin(), tx_commit(), tx_rollback(), tx_close() (and so on...) do not specify "handlers" necessary to distinguish connection objects. 4. The TX API design does not take into account the concept of "persistent connection" and "connection pool". I afforded issues 1 and 2 creating a global experimental patch for PHP core itself (you can find it in "ext/php" directory of LIXA tarball or directly at SVN repository. http://lixa.svn.sourceforge.net/viewvc/lixa/ext/php/). Issue number 3 was bypassed and, for the sake of trivial "hello world equivalent examples", the integration seems to work properly. Issue 4 is quite difficult to address: I ignored "persistent connection" disabling LIXA feature when the application asks a persistent connection, but I crashed against "connection pool" with Oracle (oci8) driver. It's time to made a balance of LIXA and PHP integration: I "successfully" integrated mysqli (with native MySQL library) and pgsql drivers. There are some examples and 7 case tests available. I was not able to figure out a smart patch for "oci8" driver and I stopped my effort. To conclude, I think 98% of the use cases does *not* need two phase commit. But if you are developing the other 2% of the use cases - without two phase commit - you probably could create some clumsy "solution" to avoid the "two phase commit issue". What do you think about PHP and two phase commit? Do you think the game isn't worth the candle? Or do you think there's room for two phase commit inside the PHP arena? In the next future I will concentrate my LIXA efforts in expanding the number of different Resource Managers for C programmers because "patching" PHP for LIXA integration is a too hard task for me myself. Is there someone interested in picking-up LIXA PHP experimental extension and going further with the task? Is there someone interested in "two phase commit" and "distributed transaction processing" in general? Every comment/hint/suggestion would be appreciated. Regards Ch.F. -- PHP Database Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
