NAME
Apache::GTopLimit - Limit Apache httpd processes
SYNOPSIS
This module allows you to kill off Apache httpd processes if they grow
too large or have too little of shared memory. You can choose to set up
the process size limiter to check the process size on every request:
# in your startup.pl:
# ___________________
use Apache::GTopLimit;
# Control the life based on memory size
# in KB, so this is ~10MB
$Apache::GTopLimit::MAX_PROCESS_SIZE = 10000;
# Control the life based on Shared memory size
# in KB, so this is ~4MB
$Apache::GTopLimit::MIN_PROCESS_SHARED_SIZE = 4000;
# Control the life based on UnShared memory size
# in KB, so this is ~6MB
$Apache::GTopLimit::MAX_PROCESS_UNSHARED_SIZE = 6000;
# in your httpd.conf:
# ___________________
# debug mode must be set before the module is loaded
PerlSetVar Apache::GTopLimit::DEBUG 1
# register handler
PerlFixupHandler Apache::GTopLimit
# 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 or
unshared. This way of checking is also easier for those who are mostly
just running Apache::Registry scripts:
# in your handler/CGI script
use Apache::GTopLimit;
# Max Process Size in KB
Apache::GTopLimit->set_max_size(10000);
and/or
use Apache::GTopLimit;
# Min Shared process Size in KB
Apache::GTopLimit->set_min_shared_size(4000);
and/or
use Apache::GTopLimit;
# Min UnShared process Size in KB
Apache::GTopLimit->set_max_unshared_size(6000);
Since accessing the process info might add a little overhead, you may
want to only check the process size every N times. To do so, put this in
your startup.pl or CGI:
$Apache::GTopLimit::CHECK_EVERY_N_REQUESTS = 2;
This will only check the process size every other time the process size
checker is called.
Note: The "MAX_PROCESS_SIZE", "MIN_PROCESS_SHARED_SIZE" and
"MAX_PROCESS_UNSHARED_SIZE" are independent, and each will be checked if
only set. So if you set the first two -- the process can be killed if it
grows beyond the limit or its shared memory goes below the limit. It's
better not to mix "MAX_PROCESS_UNSHARED_SIZE" with the first two.
DESCRIPTION
This module will run on platforms supported by GTop.pm a Perl interface
to libgtop (which in turn needs libgtop : See
http://home-of-linux.org/gnome/libgtop/ ).
This module was written in response to questions on the mod_perl mailing
list on how to tell the httpd process to exit if:
* its memory size goes beyond a specified limit
* its shared memory size goes below a specified limit
* its unshared memory size goes beyond a specified limit
Limiting memory size
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 (or leaks 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.
Limiting shared memory size
We want the reverse the above limit for a shared memory limitation and
kill the process when its hs too little of shared memory.
When the same memory page is being shared between many processes, you
need less physical memory relative to the case where the each process
will have its own copy of the memory page.
If your OS supports shared memory you will get a great benefit when you
deploy this feature. With mod_perl you enable it by preloading the
modules at the server startup. When you do that, each child uses the
same memory page as the parent does, after it forks. The memory pages
get unshared when a child modifies the page and it can no longer be
shared, that's when the page is being copied to the child's domain and
then modified as it pleased to. When this happens a child uses more real
memory and less shared.
Because of Perl's nature, memory pages get unshared pretty fast, when
the code is being executed and it's internal data is being modified.
That's why as the child gets older the size of the shared memory goes
down.
You can tune your server to kill off the child when its shared memory is
too low, but it demands a constant retuning of the configuration
directives if you do any heavy updates in the code the server executes.
This module allows you to save up the time to make this tuning and
retuning, by simply specifying the minimum size of the shared memory for
each process. And when it crosses the line, to kill it off.
Finally instead of trying to tune the memory size and shared memory
thresholds, it's much easier to only specify the amount of unshared
memory that can be tolerated and kill the process which has too much of
unshared memory.
AUTHOR
Stas Bekman <stas@stason.org>
An almost complete rewrite of "Apache::SizeLimit" toward using GTop
module (based on crossplatfom glibtop). The moment glibtop will be
ported on all the platforms "Apache::SizeLimit" runs at (I think only
Solaris is missing) "Apache::SizeLimit" will become absolete.
Doug Bagley wrote the original "Apache::SizeLimit"
CHANGES
See external file 'Changes'.
COPYRIGHT
The "Apache::GTopLimit" module is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.