[php-maint] Bug#618462: Bug#618462: php5: Large quantities of timezone file stat() calls causing possible regression

[Ondřej Surý]

Erik,

I have checked some of my all records and is there a chance that you
call timelib_timezone_id_is_valid() ?

I found this in my old records:

1. Added overhead when timezone is not set -> I don't think we should
really do anything in here. It's a simple matter of adding
date_default_timezone_set("xxx/yyy") to your application. After adding
this call PHP will use that value as first in guess_timezone().
However we could put something about it to README.Debian.

2. We call stat() everytime timelib_timezone_id_is_valid() is called.
That is adds some slowdown, but I don't really see a way how to fix
that unless you readahead all timezones, which will make PHP even more
slower (mainly at startup, but that happens basically every time with
non-threaded model).

O.

On Mon, Mar 5, 2012 at 21:08, Erik Jacobson <azhrarn at underhanded.org> wrote:
> Package: php5
> Version: 5.3.10-1
> Severity: normal
>
>
> Hi, while trying to narrow down possible causes of Apache child wait
> states, I came across this possible issue with PHP apparently calling
> stat() against the system timezone files repeatedly.  This bug seems to
> be primarily with tz init/searching looking at *all* the timezone files
> with a question as to if it's a performance impact.
>
> My issue is related but slightly different.
>
> On a loaded server with ~150 php page requests a second, I was showing
> an unusual amount of stat() calls in a child strace like so:
>
>
> www-data 27168  0.7  0.1 321968 21780 ?        SN   13:04   0:02  \_ /usr/sbin/apache2 -k start
>
> # strace -p 27168  -f -c
> Process 27168 attached - interrupt to quit
>
> ^CProcess 27168 detached
> % time     seconds  usecs/call     calls    errors syscall
> ------ ----------- ----------- --------- --------- ----------------
>  33.95    0.042694           3     12898       375 stat
>  25.95    0.032636           1     42586           select
>  6.68    0.008394           3      2893           munmap
>  5.15    0.006479           0     21928           sendto
>
> Doing an strace dump and analyzing the stat calls pointed some at htaccess and include path
> searches, but the vast majority were calls like so:
>
> stat("/usr/share/zoneinfo/America/New_York", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
> stat("/usr/share/zoneinfo/America/New_York", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
> stat("/usr/share/zoneinfo/America/New_York", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
> stat("/usr/share/zoneinfo/America/New_York", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
> stat("/usr/share/zoneinfo/America/New_York", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
> stat("/usr/share/zoneinfo/America/New_York", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
> stat("/usr/share/zoneinfo/America/New_York", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
> stat("/usr/share/zoneinfo/America/New_York", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
>
> The above block of calls were contiguous, all in less then a second.
> Blocks like the above seem to roll through more then once a minute, and
> individual stat() calls to the same file seem to appear once every 10-20
> syscalls. The above identical lookup is the vast majority of the listed
> stat calls in strace.
>
> This is in a SINGLE child thread, out of *hundreds* of active threads.
> The end result is thousands of stat calls a second.. To the same file.
> Which never changes. And is never cached in APC. I haven't been able
> to test the above load with switching to UTC and hoping it doesn't
> try to lookup the file, as our current setup relies on local time for
> certain operations (ugh).
>
> I'm currently recompiling PHP to take advantage of their timezonedb lib,
> and hoping it keeps everything in ram.  Either that or I put the
> timezone directory in a ramdisk and hoping for the best.
>
>
> -- System Information:
> Debian Release: 6.0
>  APT prefers unstable
>  APT policy: (500, 'unstable')
> Architecture: amd64 (x86_64)
>
> Kernel: Linux 2.6.32-5-amd64 (SMP w/4 CPU cores)
>
> Versions of packages php5 depends on:
> ii  libapache2-mod-php5           5.3.10-1   server-side, HTML-embedded scripti
> ii  php5-common                   5.3.10-1   Common files for packages built fr
>
> php5 recommends no packages.
>
> php5 suggests no packages.
>
> -- no debconf information
>
>
>
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-- 
Ondřej Surý <ondrej at sury.org>