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Apache2::SizeLimit(3pm) - phpMan

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

       Apache2::SizeLimit - Because size does matter.

           PerlLoadModule Apache2::SizeLimit

            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

           PerlCleanupHandler Apache2::SizeLimit

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

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

           For httpd 1.3.x / mod_perl 1.x Apache::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 "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

   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

               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.

       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 "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

       Copy-on-write and Shared Memory

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

           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();
             $r->print("1: size=$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 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".

       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 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

       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

       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

       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.

       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> 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.

       Doug Bagley <doug+modperl AT bagley.org>, channeling Procrustes.

       Brian Moseley <ix AT maz.org>: Solaris 2.6 support

       Doug Steinwand and Perrin Harkins <perrin AT elem.com>: added support for shared memory and
       additional diagnostic info

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

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

perl v5.20.2                                2012-04-03                    Apache2::SizeLimit(3pm)

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