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
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 SAPItime()but uses the syscalltime()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
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.diffAndi
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 SAPItime()but uses the syscalltime()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
realpath_cache_ttl - Time to live for cache entry (default 120 seconds; if
set to 0 then doesn't refresh).
Ah, didn't grok the TTL at first glance.... that fairly well negates the
need for an explicit flush.... If the FS layout needs to change all one
would have to do is turn down the TTL, make the change, and turn it back up
after the cache is sure to be cleared...
-Sara
Sara Golemon wrote:
realpath_cache_ttl - Time to live for cache entry (default 120 seconds; if
set to 0 then doesn't refresh).Ah, didn't grok the TTL at first glance.... that fairly well negates the
need for an explicit flush.... If the FS layout needs to change all one
would have to do is turn down the TTL, make the change, and turn it back up
after the cache is sure to be cleared...
Hmm.. if I understand correctly then one can only turn it down to 1
second as 0 means unlimited. So if an application changes the tree it
would have to sleep(1) for it to happen.
I'd strongly suggest that we have an explicit flush option. And no, I
don't think restarting the server is an opton as this can't be done from
inside an application.
BTW: This needs to be well documented as running into caching problems
can cause a very annoying debugging sessions due to the Heisenbug
nature. Happened to more than one person I know with filesize() with
missing clearstatcache() calls. One of PHP's main feature is programmer
efficiency so we should be careful to add optimizations which make
things harder for programmers.
- Chris
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Hello,
Btw, cool patch. :-) I'll see if we can start testing this in an experimental
ebuild in Gentoo land.
Sara Golemon wrote:
realpath_cache_ttl - Time to live for cache entry (default 120 seconds;
if set to 0 then doesn't refresh).Ah, didn't grok the TTL at first glance.... that fairly well negates the
need for an explicit flush.... If the FS layout needs to change all one
would have to do is turn down the TTL, make the change, and turn it back
up after the cache is sure to be cleared...Hmm.. if I understand correctly then one can only turn it down to 1
second as 0 means unlimited. So if an application changes the tree it
would have to sleep(1) for it to happen.
In real life, that would only mean a 'broken' path for 1 second. And changing
path's on a production system doesn't happen all that regularly, in my
experience.
On busy sites, a lot of users could get that broken file (not exist,
whatever), but if you don't code realpath() file i/o related correctly i.e.,
checking the file open'ed ok at least, (and in the stat()/is_*() case)
checking the file size, you're toast anyway. ;-)
I'd strongly suggest that we have an explicit flush option. And no, I
don't think restarting the server is an opton as this can't be done from
inside an application.
Same here, if it counts. ;-) For those short-by-1-second cases, and during
development, t'would be handy.
Elfyn
Elfyn McBratney
beu on irc.freenode.net/savannah.[non]gnu.org
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