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Apache::SizeLimit(3)  User Contributed Perl Documentation Apache::SizeLimit(3)

       Apache::SizeLimit - Because size	does matter.

	   PerlModule Apache::SizeLimit

	    Apache::SizeLimit->set_max_process_size(150_000);	# Max size in KB
	    Apache::SizeLimit->set_min_shared_size(10_000);	# Min share in KB
	    Apache::SizeLimit->set_max_unshared_size(120_000);	# Max unshared size in KB

	   PerlCleanupHandler Apache::SizeLimit

       ********************************	NOIICE *******************

	  This version is only for httpd 1.3.x and mod_perl 1.x

	  For httpd 2.x	/ mod_perl 2.x Apache2::SizeLimit
	  documentation	please read the	perldoc	in

       ********************************	NOTICE *******************

       This module allows you to kill off Apache httpd processes if they grow
       too large. You can make the decision to kill a process based on its
       overall size, by	setting	a minimum limit	on shared memory, or a maximum
       on unshared memory.

       You can set limits for each of these sizes, and if any limit is
       exceeded, the process will be killed.

       You can also limit the frequency	that these sizes are checked so	that
       this module only	checks every N requests.

       This module is highly platform dependent, please	read the "PER-PLATFORM
       BEHAVIOR" section for details. It is possible that this module simply
       does not	support	your platform.

       You can set set the size	limits from a Perl module or script loaded by
       Apache by calling the appropriate class method on "Apache::SizeLimit":

       o   Apache::SizeLimit->set_max_process_size($size)

	   This	sets the maximum size of the process, including	both shared
	   and unshared	memory.

       o   Apache::SizeLimit->set_max_unshared_size($size)

	   This	sets the maximum amount	of unshared memory the process can

       o   Apache::SizeLimit->set_min_shared_size($size)

	   This	sets the minimum amount	of shared memory the process must

       The two methods related to shared memory	size are effectively a no-op
       if the module cannot determine the shared memory	size for your
       platform. See "PER-PLATFORM BEHAVIOR" for more details.

   Running the handler()
       There are several ways to make this module actually run the code	to
       kill a process.

       The simplest is to make "Apache::SizeLimit" a "PerlCleanupHandler" in
       your Apache config:

	   PerlCleanupHandler Apache::SizeLimit

       This will ensure	that "Apache::SizeLimit->handler()" is run for all

       If you want to combine this module with a cleanup handler of your own,
       make sure that "Apache::SizeLimit" is the last handler run:

	   PerlCleanupHandler  Apache::SizeLimit My::CleanupHandler

       Remember, mod_perl will run stacked handlers from right to left,	as
       they're defined in your configuration.

       If you have some	cleanup	code you need to run, but stacked handlers
       aren't appropriate for your setup, you can also explicitly call the
       "Apache::SizeLimit->handler()" function from your own cleanup handler:

	   package My::CleanupHandler

	   sub handler {
	       my $r = shift;

	       # Causes	File::Temp to remove any temp dirs created during the
	       # request

	       return Apache::SizeLimit->handler($r);

       o   Apache::SizeLimit->add_cleanup_handler($r)

	   You can call	this method inside a request to	run
	   "Apache::SizeLimit"'s "handler()" method for	just that request.
	   It's	safe to	call this method repeatedly -- the cleanup will	only
	   be run once per request.

   Checking Every N Requests
       Since checking the process size can take	a few system calls on some
       platforms (e.g. linux), you may not want	to check the process size for
       every request.

       o   Apache::SizeLimit->set_check_interval($interval)

	   Calling this	causes "Apache::SizeLimit" to only check the process
	   size	every $interval	requests. If you want this to affect all
	   processes, make sure	to call	this during server startup.

       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 docs at

       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 highly platform dependent, since finding the size	of a
       process is different for	each 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, patches are very welcome.

       Currently supported OSes:

       For linux we read the process size out of /proc/self/statm. If you are
       worried about performance, you can consider using
       "Apache::SizeLimit->set_check_interval()" to reduce how often this read

       As of linux 2.6,	/proc/self/statm does not report the amount of memory
       shared by the copy-on-write mechanism as	shared memory. This means that
       decisions made based on shared memory as	reported by that interface are
       inherently wrong.

       However,	as of the 2.6.14 release of the	kernel,	there is
       /proc/self/smaps	entry for each process.	/proc/self/smaps reports
       various sizes for each memory segment of	a process and allows us	to
       count the amount	of shared memory correctly.

       If "Apache::SizeLimit" detects a	kernel that supports /proc/self/smaps
       and the "Linux::Smaps" module is	installed it will use that module
       instead of /proc/self/statm.

       Reading /proc/self/smaps	is expensive compared to /proc/self/statm. It
       must look at each page table entry of a process.	 Further, on
       multiprocessor systems the access is synchronized with spinlocks.
       Again, you might	consider using

       Copy-on-write and Shared	Memory

       The following example shows the effect of copy-on-write:

	   require Apache::SizeLimit;
	   package X;
	   use strict;
	   use Apache::Constants qw(OK);

	   my $x = "a" x (1024*1024);

	   sub handler {
	     my	$r = shift;
	     my	($size,	$shared) = $Apache::SizeLimit->_check_size();
	     $x	=~ tr/a/b/;
	     my	($size2, $shared2) = $Apache::SizeLimit->_check_size();
	     $r->print("1: size=$size shared=$shared\n");
	     $r->print("2: size=$size2 shared=$shared2\n");
	     return OK;

	 <Location /X>
	   SetHandler modperl
	   PerlResponseHandler X

       The parent Apache process allocates memory for the string in $x.	The
       "tr"-command then overwrites all	"a" with "b" if	the handler is called
       with an argument. This write is done in place, thus, the	process	size
       doesn't change. Only $x is not shared anymore by	means of copy-on-write
       between the parent and the child.

       If /proc/self/smaps is available	curl shows:

	 r2@s93:~/work/mp2> curl http://localhost:8181/X
	 1: size=13452 shared=7456
	 2: size=13452 shared=6432

       Shared memory has lost 1024 kB. The process' overall size remains

       Without /proc/self/smaps	it says:

	 r2@s93:~/work/mp2> curl http://localhost:8181/X
	 1: size=13052 shared=3628
	 2: size=13052 shared=3636

       One can see the kernel lies about the shared memory. It simply doesn't
       count copy-on-write pages as shared.

   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?

   BSD (and OSX)
       Uses "BSD::Resource::getrusage()" to determine process size.  This is
       pretty efficient	(a lot more efficient than reading it from the /proc
       fs anyway).

       According to recent tests on OSX	(July, 2006), "BSD::Resource" simply
       reports zero for	process	and shared size	on that	platform, so OSX is
       not supported by	"Apache::SizeLimit".

       Uses "BSD::Resource::getrusage()" to determine process size.  Not sure
       if the shared memory calculations will work or not.  AIX	users?

       Uses "Win32::API" to access process memory information.	"Win32::API"
       can be installed	under ActiveState perl using the supplied ppm utility.

   Everything Else
       If your platform	is not supported, then please send a patch to check
       the process size. The more portable/efficient/correct the solution the
       better, of course.

       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

       Actually, there are two big reasons your	httpd children will grow.
       First, your code	could have a bug that causes the process to increase
       in size very quickly. Second, you could just be doing operations	that
       require a lot of	memory for each	request. Since Perl does not give
       memory back to the system after using it, the process size can grow
       quite large.

       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 kill your memory gobbling processes.
       However,	it is a	little violent,	terminating your process in mid-

       This module attempts to solve the second	situation, where your process
       slowly grows over time. It checks memory	usage after every request, and
       if it exceeds a threshold, exits	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.

       Previous	versions of this module	documented three globals for defining
       memory size limits:

       o   $Apache::SizeLimit::MAX_PROCESS_SIZE

       o   $Apache::SizeLimit::MIN_SHARE_SIZE

       o   $Apache::SizeLimit::MAX_UNSHARED_SIZE

       o   $Apache::SizeLimit::CHECK_EVERY_N_REQUESTS

       o   $Apache::SizeLimit::USE_SMAPS

       Direct use of these globals is deprecated, but will continue to work
       for the foreseeable future.

       It also documented three	functions for use from registry	scripts:

       o   Apache::SizeLimit::setmax()

       o   Apache::SizeLimit::setmin()

       o   Apache::SizeLimit::setmax_unshared()

       Besides setting the appropriate limit, these functions also add a
       cleanup handler to the current request.

       The Apache-SizeLimit project is co-maintained by	several	developers,
       who take	turns at making	CPAN releases. Therefore you may find several
       CPAN directories	containing Apache-SizeLimit releases. The best way to
       find the	latest release is to use

       If you have a question or you want to submit a bug report or make a
       contribution, please do not email individual authors, but send an email
       to the modperl <at> mailing list. This list is
       moderated, so unless you	are subscribed to it, your message will	have
       to be approved first by a moderator. Therefore please allow some	time
       (up to a	few days) for your post	to propagate to	the list.

       Doug Bagley <>, channeling Procrustes.

       Brian Moseley <>: Solaris 2.6 support

       Doug Steinwand and Perrin Harkins <>: added support for
       shared memory and additional diagnostic info

       Matt Phillips <> and	Mohamed	Hendawi
       <>: Win32 support

       Dave Rolsky <>, maintenance and fixes outside of
       mod_perl	tree (0.9+).

perl v5.32.0			  2019-10-05		  Apache::SizeLimit(3)


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