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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;
# watch what happens
$Apache::GTopLimit::DEBUG = 1;
# in your httpd.conf:
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 CGI:
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);
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 and MIN_PROCESS_SHARED_SIZE are standalone,
and each will be checked if only set. So if you set both -- the
process
can be killed if it grows beyond the limit or its shared memory goes
below the limit.
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
Limiting memory size
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.
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.
AUTHOR
Stas Bekman <[EMAIL PROTECTED]>:
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'.
______________________________________________________________________
Stas Bekman | JAm_pH -- Just Another mod_perl Hacker
http://stason.org/ | mod_perl Guide http://perl.apache.org/guide/
mailto:[EMAIL PROTECTED] | http://perl.org http://stason.org/TULARC/
http://singlesheaven.com| http://perlmonth.com http://sourcegarden.org
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