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Date: Tue, 21 Sep 2004 12:02:15 -0700
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Subject: Re: [PHP-DEV] realpath() caching
From: andi@zend.com (Andi Gutmans)

I was asked to provide some more info about this patch.
In general, PHP does a realpath() on files (most importantly included 
files) so that when include_once() and other PHP functionality needs to 
know if two file paths are identical it will give a definite answer. 
realpath() itself is quite a slow function (especially on some specific OS) 
and therefore should be saved when possible.
As it is rare that a realpath() for a certain file path + cwd combination 
ever changes, it's a perfect candidate for caching (actually a realpath() 
can only really change if you are adding/changing symlinks).
Therefore, this patch implements caching of realpath() calls. There are two 
INI settings which can be changed:
realpath_cache_size - Size of cache (default's to 16K; if set to 0 it turns 
of caching).
realpath_cache_ttl - Time to live for cache entry (default 120 seconds; if 
set to 0 then doesn't refresh).

On a loaded side even a small TTL should do the trick, although it might 
make sense to raise the TTL to something much higher than 120 seconds 
because as I said, it doesn't usually change.
Hope that's enough info.
Andi




At 07:24 PM 9/20/2004 -0700, Andi Gutmans wrote:
>Thanks for pointing out that the attachment didn't make it through. You 
>can find it at:
>http://snaps.php.net/~andi/realpath_cache2.diff
>
>Andi
>
>At 06:28 PM 9/20/2004 -0700, Andi Gutmans wrote:
>>Hi,
>>
>>Attached is the promised patch to do realpath() caching.
>>You can set cache size and TTL via the php.ini (default is 2 minutes TTL 
>>and 16K memory).
>>It doesn't use the SAPI time() but uses the syscall time() because it 
>>seemed to be slightly faster but we can adjust it to use the SAPI one if 
>>anyone measures a difference in performance (might depend on the OS).
>>
>>Feedback welcome.
>>Also any feedback on the VM patch? I'd like to commit it soon but I 
>>haven't heard anything from this list (people were saying they wanted to 
>>review it).
>>
>>Thanks,
>>Andi
>>
>>
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