Apache::SizeLimit(3p) User Contributed Perl DocumentationApache::SizeLimit(3p)



NAME
       Apache::SizeLimit - Because size does matter.

SYNOPSIS
           <Perl>
            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
           </Perl>

           PerlCleanupHandler Apache::SizeLimit

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

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

           Future versions of this module may support both.

           Currently, Apache2::SizeLimit is bundled with
           mod_perl 2.x for that series.

       ******************************** 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 "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
           use.

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

           PerlCleanupHandler Apache::SizeLimit

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

       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
               File::Temp::cleanup();

               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.

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

       Copy-on-write and Shared Memory

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

         <Perl>
           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->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 "Apache::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:

       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.

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 v5.12.2                      2007-03-26             Apache::SizeLimit(3p)
