Sean Pringle wrote: >> The Caching systems such as Zend Cache (not the Optimizer), MMCache, >> APC, etc are expressly designed to store the tokenized version of the >> PHP script to be executed. >> >> Note that their REAL performance savings is actually in loading from >> the hard drive into RAM, not actually the PHP tokenization. >> >> Skipping a hard drive seek and read is probably at least 95% of the >> savings, even in the longest real-world scripts. > > Interesting. If PHP tokenization is such a small cost, what makes a > special caching system better than the OS for caching files in memory > after the first disk read? APC actually executes the opcodes directly in shared memory, so unlike a disk cache, you are not copying lots of stuff around. APC does need to copy some things down into process-local memory, but most can be left where it is. Disk caches also tend to expire pretty fast because everything your OS does tends to touch the disk and when you application starts eating memory your disk cache is the first to go when things get tight. With a dedicated shared memory segment that won't happen. Things will stay put. It is also possible to run APC in no-stat mode which means it will never touch the disk at all. If you are on an Intel cpu with an older OS like freebsd4, disk-touching syscalls are massively slow and you can gain a lot by skipping the up-to-date stat check on each request and include file. Finally the compiler does more than just tokenize your script. It will cache functions and classes when it can and rewrite the opcodes so these functions and classes won't have to be created at execution time. Of course, that assumes you haven't gone all framework-crazy and made everything dynamic with autoload or weird conditional function and class declarations. If it becomes a runtime decision whether class or a function is declared, or heaven forbid, the same class takes on different signatures based on some runtime condition, then there isn't much the compiler can do to speed that up. -Rasmus -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
