Hi Brendon, In our environment, we use NFS for shared storage, we are using APC as well with stat=0. In our setting, we also experiencing high number of stat() calls on our file system. My initial finding of this problem is we enabled the open_basedir setting. And there is already a bug report for this, https://bugs.php.net/bug.php?id=52312
We tested the issue in 5.2.x, 5.3.x and 5.4.x, all of them experiencing same issue. I m not sure if this is a same problem as yours. But I do hope the community can find out a good solutions to handle the balance of better security and good performance. Cheers On Tue, Feb 19, 2013 at 7:26 AM, Brendon Colby <bren...@newgrounds.com>wrote: > Greetings, > > This seemed like the appropriate list to discuss this - let me know if it > isn't. > > We have several Apache 2.2 / PHP 5.4 / APC 3.1.13 servers all serving > mostly PHP over NFS (we have separate servers for static content). I > have been trying to figure out why we're seeing so many getattr > requests from our Apache/PHP servers. I think I've narrowed it down to > how PHP/APC gets information about a file to see if it has been > changed since it was last cached: > > https://bugs.php.net/bug.php?id=59372 > > Rasmus said: > > "Just because you see an open() syscall doesn't mean the cache isn't > used. The open() is there because PHP by default does open+fstat for > performance reasons. If you look carefully you will see there is just > an open() and no read() calls. So it opens the file, uses the stat > struct from the open fd to get the inode and fetches the op_array from > the opcode cache. This can be made more efficient, but this report is > incorrect in assuming the cache isn't being used." > > This is exactly what I'm seeing when I strace an httpd process - > mostly open() and fstat() calls w/o any read() calls. This makes sense > to me, however, the problem with this is as far as I understand it, > that an open() on an NFS file system causes an automatic gettattr() > call to the server. Doing this completely bypasses the NFS attribute > cache, which is why we're seeing so many getattr requests to our NFS > server despite having an attribute cache timeout of 60 seconds. For > those familiar with NFS, we could just as well disable our attribute > cache at this point, which is almost never recommended because of > performance reasons. > > I found a good explaination of why this happens in this Redhat document: > > > http://www.redhat.com/rhecm/rest-rhecm/jcr/repository/collaboration/jcr:system/jcr:versionStorage/5e75391d7f00000110a97b91452f0cee/1/jcr:frozenNode/rh:pdfFile.pdf > > "Avoid unnecessarily opening and closing of files. If you access a > file frequently, opening and closing that file triggers the > opentoclose cache > consistency mechanism in the NFS file system. Triggering this > mechanism causes NFS getattr requests to be generated, which can slow > performance. By keeping the file open, traffic is kept to a minimum." > > I've tried doing apc.stat=0 and about every other combination of > options, but PHP still does an open()+3 fstat() commands on every > single page load no matter what I do. We have autoload set, so that > equates to several automatic open() (and subsequent NFS getattr()) > calls with every single PHP request. To give you an idea what kind of > load this is generating for us: > > -Out of 7,000 total NFS operations per second right now: > -About 45% are getattr calls > -Our Apache/PHP servers are generating 52% of all NFS calls > -An average of 82% of those calls are getattr requests > -As a comparison, our far busier content servers (many times the req/s > of the Apache/PHP servers) are generating half the number of NFS > requests our PHP servers are, and 98% or so of those requests are read > requests with just 1% getattr > > I am pretty proficient with patching/compiling/profiling, but sadly I > am no C coder. I've tried digging into this myself but I'm pretty out > of my element here. I'm curious if anyone on this list could give me > any pointers on what I can do to change this behavior and reduce the > load on our NFS server. If we can't change PHP behavior, we may have > to abandon NFS for our PHP files due to the load PHP appears to be > generating on our NFS server. I'd hate to do this, so please let me > know if any of you have any ideas as to what I can do to change this > behavior. > > Brendon > > -- > PHP Internals - PHP Runtime Development Mailing List > To unsubscribe, visit: http://www.php.net/unsub.php > >
