[FIXED] Why is file_get_contents faster than memcache_get?

Issue

I'm loading XML files from disk using file_get_contents, and as a test I find I can load a 156K file using file_get_contents() 1,000 times in 3.99 seconds. I've subclassed the part that does the loading and replaced it with a memcache layer, and on my dev machine find I can do 1000 loads of the same document in 4.54 seconds.

I appreciate that file_get_contents() will do some caching, but it looks like it is actually faster than a well-known caching technique. On a single server, is the performance of file_get_contents() as good as one can get?

I'm on PHP 5.2.17 via Macports, OS X 10.6.8.

Edit: I've found on XML documents of this size, there is a small benefit to be had in using the MEMCACHE_COMPRESSED flag. 1,500 loads via memcache are done in 6.44 sec (with compression) rather than 6.74 (without). However both are slower than file_get_contents, which does the same number of loads in 5.71 sec.

Solution

Because file_get_contents mmaps the file and so you'll only have a few file system calls and this will end up in the file system cache. memcache involves out-of-process calls to the memcached (and out of server on a clustered implementation).

The performance of file_get_contents() crucially depends on the type of file system, for example a file on an NFS mounted file system is not mmapped and this access can be a LOT slower. Also on a multi-user server, the file system cache can get rapidly flushed by other processes whereas the memcached cache will almost certainly be in memory.

Answered By - TerryE

Answer Checked By - Terry (PHPFixing Volunteer)