Apache::SizeLimUser)Contributed Perl DocumentApache::SizeLimit(3)NAMEApache::SizeLimit - Because size does matter.
SYNOPSIS
This module allows you to kill off Apache httpd processes
if they grow too large. You can choose to set up the pro
cess size limiter to check the process size on every
request:
# in your startup.pl:
use Apache::SizeLimit;
# sizes are in KB
$Apache::SizeLimit::MAX_PROCESS_SIZE = 10000; # 10MB
$Apache::SizeLimit::MIN_SHARE_SIZE = 1000; # 1MB
$Apache::SizeLimit::MAX_UNSHARED_SIZE = 12000; # 12MB
# in your httpd.conf:
PerlFixupHandler Apache::SizeLimit
# you can set this up as any Perl*Handler that handles part of the
# request, even the LogHandler will do.
Or you can just check those requests that are likely to
get big, such as CGI requests. This way of checking is
also easier for those who are mostly just running
CGI.pm/Registry scripts:
# in your CGI:
use Apache::SizeLimit;
&Apache::SizeLimit::setmax(10000); # Max size in KB
&Apache::SizeLimit::setmin(1000); # Min share in KB
&Apache::SizeLimit::setmax_unshared(12000); # Max unshared size in KB
Since checking the process size can take a few system
calls on some platforms (e.g. linux), you may want to only
check the process size every N times. To do so, put this
in your startup.pl or CGI:
$Apache::SizeLimit::CHECK_EVERY_N_REQUESTS = 2;
This will only check the process size every other time the
process size checker is called.
DESCRIPTION
This module is highly platform dependent, please read the
CAVEATS section.
This module was written in response to questions on the
mod_perl mailing list on how to tell the httpd process to
exit if it gets too big.
Actually there are two big reasons your httpd children
will grow. First, it could have a bug that causes the
process to increase in size dramatically, until your sys
tem starts swapping. Second, your process just does stuff
that requires a lot of memory, and the more different
kinds of requests your server handles, the larger the
httpd processes grow over time.
This module will not really help you with the first prob
lem. For that you should probably look into
Apache::Resource or some other means of setting a limit on
the data size of your program. BSD-ish systems have
setrlimit() which will croak your memory gobbling pro
cesses. However it is a little violent, terminating your
process in mid-request.
This module attempts to solve the second situation where
your process slowly grows over time. The idea is to check
the memory usage after every request, and if it exceeds a
threshold, exit gracefully.
By using this module, you should be able to discontinue
using the Apache configuration directive MaxRequestsPer
Child, although for some folks, using both in combination
does the job. Personally, I just use the technique shown
in this module and set my MaxRequestsPerChild value to
6000.
SHARED MEMORY OPTIONS
In addition to simply checking the total size of a pro
cess, this module can factor in how much of the memory
used by the process is actually being shared by copy-on-
write. If you don't understand how memory is shared in
this way, take a look at the mod_perl Guide at
http://perl.apache.org/guide/.
You can take advantage of the shared memory information by
setting a minimum shared size and/or a maximum unshared
size. Experience on one heavily trafficked mod_perl site
showed that setting maximum unshared size and leaving the
others unset is the most effective policy. This is
because it only kills off processes that are truly using
too much physical RAM, allowing most processes to live
longer and reducing the process churn rate.
CAVEATS
This module is platform dependent, since finding the size
of a process is pretty different from OS to OS, and some
platforms may not be supported. In particular, the limits
on minimum shared memory and maximum shared memory are
currently only supported on Linux and BSD. If you can
contribute support for another OS, please do.
Currently supported OSes:
linux
For linux we read the process size out of
/proc/self/status. This is a little slow, but usually
not too bad. If you are worried about performance, try
only setting up the the exit handler inside CGIs (with
the "setmax" function), and see if the
CHECK_EVERY_N_REQUESTS option is of benefit.
solaris 2.6 and above
For solaris we simply retrieve the size of
/proc/self/as, which contains the address-space image
of the process, and convert to KB. Shared memory cal
culations are not supported.
NOTE: This is only known to work for solaris 2.6 and
above. Evidently the /proc filesystem has changed
between 2.5.1 and 2.6. Can anyone confirm or deny?
*bsd*
Uses BSD:\fIs0:Resource::getrusage() to determine pro
cess size. This is pretty efficient (a lot more effi
cient than reading it from the /proc fs anyway).
AIX?
Uses BSD:\fIs0:Resource::getrusage() to determine pro
cess size. Not sure if the shared memory calculations
will work or not. AIX users?
If your platform is not supported, and if you can tell me
how to check for the size of a process under your OS (in
KB), then I will add it to the list. The more
portable/efficient the solution, the better, of course.
TODO
Possibly provide a perl make/install so that the Size
Limit.pm is created at build time with only the code you
need on your platform.
If Apache was started in non-forking mode, should hitting
the size limit cause the process to exit?
AUTHOR
Doug Bagley <doug+modperl@bagley.org>, channeling Pro
crustes.
Brian Moseley <ix@maz.org>: Solaris 2.6 support
Doug Steinwand and Perrin Harkins <perrin@elem.com>: added
support
for shared memory and additional diagnostic info
2002-03-23 mod_perl-1.27 Apache::SizeLimit(3)
