PHP Performance in Apache: Multi-Process vs Multi-Threaded

Hi All, I have a few questions about the performance of PHP web applications *under load* and I would appreciate if there is anyone that would like to share their experiences in terms of any benchmarks or observations. *Background Information* In multi-process environments, such as FastCGI, Apache Prefork MPM etc, PHP needs to execute the MINIT and MSHUTDOWN functions for all loaded extensions on every request. In a multi-threaded environment, such as Apache Worker MPM, with Zend Thread Safety is enabled, PHP only needs to execute MINIT and MSHUTDOWN functions once for each extension and not each time a new thread is created to serve a request. It is also more expensive to create new processes than to create new threads. In one-on-one comparisons between scripts executed only once in ZTS mode and scripts executed once in non-ZTS mode, I noticed that the one in non-ZTS mode was slightly faster and this seems to be the main reason why most people go with the non-ZTS enabled setups. But the reason for this slight difference in speed is because of the differences in the data structure for globals for ZTS and non-ZTS modes. Other reasons people have cited for going with non-threaded setups include stability which I guess we should not really be concerned about if non-threadsafe extensions are excluded. Since it is generally more expensive to create new processes than new threads, I believe that under high load, php in ZTS mode (multi-threaded environment) will perform better than an identical setup in NTS mode (multi-process). *Problem* I noticed that Zend Server is using PHP in FastCGI mode (multi-process NTS) and I am contemplating setting up apache in worker mode (threaded mode) and compiling php in ZTS mode instead. Has anyone performed any load tests benchmarks comparing the two setups (Multi-Process vs Multi-Threaded)? Are there PHP extensions that cause issues in threaded environments that I should avoid? Are there any internals information or any other reasons why I should choose ZTS over NTS or vice versa? Any useful feedback will be highly appreciated. Thanks. -- °O° "Good Enough" is not good enough. To give anything less than your best is to sacrifice the gift. Quality First. Measure Twice. Cut Once. http://www.israelekpo.com/