Edit report at http://bugs.php.net/bug.php?id=49383&edit=1
ID: 49383
Updated by: rasmus@php.net
Reported by: olga at metacafe dot com
Summary: Lots of empty fstat() calls slow performance
Status: Bogus
Type: Bug
Package: Performance problem
Operating System: Red Hat 3.4.6-10
PHP Version: 5.3, 6
Block user comment: N
New Comment:
The reason open_basedir affects this is because for security reasons we
can't
enable the stat cache when open_basedir is enabled which will also
affect stats
after the file is opened since it isn't the open_basedir check itself
causing
the stat but the fact that the open_basedir feature forces the stat
cache to be
disabled.
The main thing that changed between 5.2.x and 5.3.x with respect to
stats is
that we rewrote the stat cache to be more efficient. It now does
intra-path
caching of realpath() lookups as opposed to just caching the return of
the
realpath() call, but it doesn't sound like this is the issue here.
One thing you can try is to compile PHP without phar support.
./configure --
disable-phar and see if that changes things. Beyond that you would need
to set
a gdb breakpoint and get a backtrace of those calls. Generally we are
not too
concerned about fstat calls since they tend to be extremely fast in most
environments. It is the full stat/lstat calls that need to hit the disk
that
tend to be slow.
Previous Comments:
------------------------------------------------------------------------
[2010-08-12 15:58:41] a dot rogge at solvention dot de
First of all: No, we don't use open_basedir or safe_mode or stuff like
that.
But I still do not understand what this has to do with the issue.
The redundant fstat() calls are obviously *not* from open_basedir,
because the fstat() calls are done after the file was opened.
I run 5.1.6, 5.2.14 and 5.3.2 with the same configuration. For 5.1.6 and
5.2.14 everything looks normally, in 5.3.2 there are suddenly three
instead of one fstat() call after opening the file. The calls are
identical and adjacent with no other syscalls in between. The two
successive calls do not provide any more information than the first one
and thus are redundant and useless.
This is obviously a performance regression. Do you want to tell me that
this is a new feature?
------------------------------------------------------------------------
[2010-08-12 01:24:32] rasmus@php.net
Do you have openbase_dir enabled? If so, for security reasons we can't
use the
stat cache which is going to cause a lot of stats. For a setup with
slow stats, I
suggest chroot/jail or something along those lines rather than
open_basedir to
keep users separated.
------------------------------------------------------------------------
[2010-08-11 20:10:56] a dot rogge at solvention dot de
Nobody cares wether or not APC works around the problem. There is
obviously a regression from 5.2 to 5.3.
Somebody maanged to triple the number of fstat() calls that are done for
an include().
Yesterday I "reproduced" the issue on our webcluster. Running the Red
Hat provided PHP 5.1.6 (from RHEL 5.5) the loadavg was around 8 for all
boxes. Upgrading to PHP 5.3.2 made the loadavg raised to values of 30 or
higher. Page load time went from < 1 second to around 30 seconds.
The best part is: we did install and configure apc for 5.3.2, but not
for 5.1.6
So eventually 5.3.2 *with* APC produces 3 times more load and needs 30
times longer than our ancient 5.1.6 *without* APC.
However, I must admit that we have our PHP-files on GFS2 where stat() is
traditionally a bit slow.
------------------------------------------------------------------------
[2010-01-21 23:16:42] rasmus@php.net
Unable to reproduce under apc.
------------------------------------------------------------------------
[2009-10-14 11:28:06] olga at metacafe dot com
The problem persists.
We upgraded APC to the latest version (3.1.3p1). Cache full count is 0,
hit ratio is 99.9%. I understand that this shouldn't happen, but there
are still 3 fstat() calls per file opened.
Here's our APC configuration - maybe you can see if anything is wrong
with it? Do you have other versions?
apc.cache_by_default 1
apc.canonicalize 1
apc.coredump_unmap 0
apc.enable_cli 1
apc.enabled 1
apc.file_md5 0
apc.file_update_protection 2
apc.filters
apc.gc_ttl 3600
apc.include_once_override 1
apc.lazy_classes 0
apc.lazy_functions 0
apc.max_file_size 1M
apc.mmap_file_mask /tmp/apc.IR76ZW
apc.num_files_hint 1024
apc.preload_path
apc.report_autofilter 0
apc.rfc1867 0
apc.rfc1867_freq 0
apc.rfc1867_name APC_UPLOAD_PROGRESS
apc.rfc1867_prefix upload_
apc.rfc1867_ttl 3600
apc.shm_segments 1
apc.shm_size 128
apc.stat 0
apc.stat_ctime 0
apc.ttl 7200
apc.use_request_time 1
apc.user_entries_hint 4096
apc.user_ttl 7200
apc.write_lock 1
------------------------------------------------------------------------
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