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Apache2::SizeLimit(3)                User Contributed Perl Documentation               Apache2::SizeLimit(3)



NAME
       Apache2::SizeLimit - Because size does matter.

SYNOPSIS
           PerlLoadModule Apache2::SizeLimit

           <Perl>
            Apache2::SizeLimit->set_max_process_size(150_000);   # Max size in KB
            Apache2::SizeLimit->set_min_shared_size(10_000);     # Min share in KB
            Apache2::SizeLimit->set_max_unshared_size(120_000);  # Max unshared size in KB
           </Perl>

           PerlCleanupHandler Apache2::SizeLimit

DESCRIPTION
       ******************************** NOIICE *******************

           This version is only for httpd 2.x and mod_perl 2.x
           series.

           For httpd 1.3.x / mod_perl 1.x Apache::SizeLimit
           documentation please read the perldoc in
           lib/Apache/SizeLimit.pm

       ******************************** 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.

API
       You can set set the size limits from a Perl module or script loaded by Apache by calling the
       appropriate class method on "Apache2::SizeLimit":

       •   Apache2::SizeLimit->set_max_process_size($size)

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

       •   Apache2::SizeLimit->set_max_unshared_size($size)

           This sets the maximum amount of unshared memory the process can use.

       •   Apache2::SizeLimit->set_min_shared_size($size)

           This sets the minimum amount of shared memory the process must have.

       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 "Apache2::SizeLimit" a "PerlCleanupHandler" in your Apache config:

           PerlCleanupHandler Apache2::SizeLimit

       This will ensure that "Apache2::SizeLimit->handler()" is run for all requests.

       If you want to combine this module with a cleanup handler of your own, make sure that
       "Apache2::SizeLimit" is the last handler run:

           PerlCleanupHandler  Apache2::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 "Apache2::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
               File::Temp::cleanup();

               return Apache2::SizeLimit->handler($r);
           }

       •   Apache2::SizeLimit->add_cleanup_handler($r)

           You can call this method inside a request to run "Apache2::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.

       •   Apache2::SizeLimit->set_check_interval($interval)

           Calling this causes "Apache2::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.

SHARED MEMORY OPTIONS
       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 http://perl.apache.org/docs/.

       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.

PER-PLATFORM BEHAVIOR
       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:

   linux
       For linux we read the process size out of /proc/self/statm. If you are worried about performance, you
       can consider using "Apache2::SizeLimit->set_check_interval()" to reduce how often this read happens.

       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 "Apache2::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 "Apache2::SizeLimit->set_check_interval()".

       Copy-on-write and Shared Memory

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

         <Perl>
           require Apache2::SizeLimit;
           package X;
           use strict;
           use Apache2::Const -compile => qw(OK);

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

           sub handler {
             my $r = shift;
             my ($size, $shared) = $Apache2::SizeLimit->_check_size();
             $x =~ tr/a/b/;
             my ($size2, $shared2) = $Apache2::SizeLimit->_check_size();
             $r->content_type('text/plain');
             $r->print("1: size=$size shared=$shared\n");
             $r->print("2: size=$size2 shared=$shared2\n");
             return OK;
           }
         </Perl>

         <Location /X>
           SetHandler modperl
           PerlResponseHandler X
         </Location>

       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 unchanged.

       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 "Apache2::SizeLimit".

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

   Win32
       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.

ABOUT THIS MODULE
       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, 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-request.

       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.

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

       •   $Apache2::SizeLimit::MAX_PROCESS_SIZE

       •   $Apache2::SizeLimit::MIN_SHARE_SIZE

       •   $Apache2::SizeLimit::MAX_UNSHARED_SIZE

       •   $Apache2::SizeLimit::CHECK_EVERY_N_REQUESTS

       •   $Apache2::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:

       •   Apache2::SizeLimit::setmax()

       •   Apache2::SizeLimit::setmin()

       •   Apache2::SizeLimit::setmax_unshared()

       Besides setting the appropriate limit, these functions also add a cleanup handler to the current
       request.  In the 2.x series of mod_perl to use the deprecated functions, you must set PerlOptions
       +GlobalRequest accordingly.

SUPPORT
       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 http://search.cpan.org/.

       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> perl.apache.org 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.

AUTHOR
       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

       Matt Phillips <mphillips@virage.com> and Mohamed Hendawi <mhendawi@virage.com>: Win32 support

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



perl v5.16.2                                     2012-04-05                            Apache2::SizeLimit(3)