Apache::SizeLimit - Because size does matter.
This module allows you to kill off Apache httpd processes if they grow too
large. You can choose to set up the process 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.
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 system 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 problem. 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 processes. 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 MaxRequestsPerChild, 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.
In addition to simply checking the total size of a process, 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.
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 calculations 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?
-
Uses BSD::Resource::getrusage() to determine process size. This is pretty
efficient (a lot more efficient than reading it from the /proc fs anyway).
- AIX?
-
Uses BSD::Resource::getrusage() to determine process 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.
Possibly provide a perl make/install so that the SizeLimit.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?
Doug Bagley <doug+modperl@bagley.org>, channeling Procrustes.
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
