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Date: Wed, 30 Sep 2009 14:14:34 -0400
Message-ID: <66887a3d0909301114j77546333lcfbcbc00fa8732ad@mail.gmail.com>
Subject: Re: huge httpd processes
From: Perrin Harkins <pharkins@gmail.com>
To: Clinton Gormley <clint@traveljury.com>
Cc: Justin Wyllie <Justin.Wyllie@sophos.com>,
	"modperl@perl.apache.org" <modperl@perl.apache.org>
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On Wed, Sep 30, 2009 at 10:47 AM, Clinton Gormley <clint@traveljury.com> wr=
ote:
>> Do either of these bear any relation to mod_perl's shared memory which
>> you can use by preloading modules at startup?
>
> Yes - as I understand it (somebody please correct me if I'm wrong), all
> of the C libraries (eg XS modules) that you preload will remain shared
> between your processes. =A0Also, your heap (Perl code and vars) will star=
t
> off as shared in a new process. =A0As each page in the heap becomes dirty=
,
> the heap will become less shared.

The short answer is that absolutely everything starts off shared
whenever you fork any program, because of copy-on-write.  Over time,
as pages get written to, they are no longer shared.

> But given that forking a new process is cheap with copy-on-write, just
> make sure that your children exit on a regular basis, eg after 1000
> requests.

I'd start with something really low and work up, like 10 requests, or
use Apache::SizeLimit.

- Perrin