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Date: Fri, 20 Mar 2015 12:13:13 +1100
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To: Rasmus Lerdorf <rasmus@lerdorf.com>
Cc: Eric Stenson <ericsten@microsoft.com>, 
	"internals@lists.php.net" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [Q] Does PHP have a negative cache for file stat operations?
From: pierre.php@gmail.com (Pierre Joye)

On Fri, Mar 20, 2015 at 12:09 PM, Rasmus Lerdorf <rasmus@lerdorf.com> wrote:
> On 03/19/2015 01:26 PM, Eric Stenson wrote:
>> PHP Internals folks--
>>
>> We're doing some performance work in WinCache, and we're finding that some frameworks are...uh...enthusiastically using file_exists(), is_file() and is_dir() functions on files/directories that don't exist.  Every. Single. Pageload.
>>
>> Does the PHP stat cache include negative cache entries?  If not, why not?
>>
>> Are there any existing extensions that implement a negative cache for file_exists(), is_file(), et. al.?
>
> We do not do negative caching. This is documented at
> http://php.net/manual/en/function.clearstatcache.php where it says:
>
>   You should also note that PHP doesn't cache information about
>   non-existent files. So, if you call file_exists() on a file that
>   doesn't exist, it will return FALSE until you create the file. If you
>   create the file, it will return TRUE even if you then delete the
>   file. However unlink() clears the cache automatically.
>
> But, I think you are also missing the fact that the stat cache is
> per-request. So your "every single pageload" aspect won't be helped by
> adding negative caching to the stat cache. It is still going to stat on
> every single page load. It is only multiple identical stats within the
> same request that gets caught by the stat cache.

Thanks :)  I forgot to mention that here (but in a chat :).

Also it would help a little bit as some apps repeatedly check files or
paths in the same request. However I am not sure it is worth the
addition.

Cheers,
-- 
Pierre

@pierrejoye | http://www.libgd.org