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Posted at 12:52PM Oct 26, 2009 by Basant Kukreja in php  |  Comments[0]

Caching file_get_contents output inside APC.

APC creates a mmap which is used for caching compiled php response. Besides this APC provides API to cache user data into this mmap. There are many php apps which uses file_get_contents to read the static files. If APC can cache these files in it's mmap, it will improve file_get_contents performance.

Based on the above idea, I developed a patch which stores the file_get_content output in APC's cache. In this patch, APC intercepts the calls of file_get_contents and replaces it with apc_file_get_contents function. If file is a full path and entire file is requested then APC caches the content.

To enable the caching use the following in php.ini :
apc.cache_static_contents=1
apc.user_ttl = 30

apc.user_ttl will decide how long the entry will remain inside the cache.  If apc.user_ttl is set to 0 then the entry will never be removed from cache.

Here is the performance data collected using Studio 12 on Solaris sparc for ecommerce php benchmark. (3500 simultaneous users)

Run	Excl. User CPU  sec.	Incl. User CPU sec.	Excl. Total LWP  sec.	Incl. Total LWP  sec.	Excl. Sys. CPU sec.	Incl. Sys. CPU sec.	Name
Without  Cache	0.831	28.660	1.141	540.018	0.030	344.311	zif_file_get_contents
With Cache	1.481	181.537	1.821	282.758	0.140	12.449	zif_apc_file_get_contents

User + System time before Caching = 372 seconds
User + System time after Caching = 193 seconds
Total time reduction in file_cache_contents = 48%

When static file is inside the cache then server will not do any stat calls. Which means if file changes then cache will still serve the old cached file during apc.user_ttl interval.

Posted at 12:51PM Oct 26, 2009 by Basant Kukreja in php  |  Comments[0]