[MP1] Memory usage(eating, leaking)

["Ruslan U. Zakirov" <cu...@wildgate.miee.ru>]

        Hi, all.
I'm looking for suggestions, information, may be atricles about 
different memory usage issues concerned with mod_perl1.
On one Russian forum man posted an review of memory "leaks"(caveats):

sub handler
{
        my $r = shift;
        $r->send_http_header('text/plain');
        print "Hello, World!\n";
        print ttt();
        return OK;
}
sub ttt
{
    my $huge_text = 'x' x 1000000;
    my $huge_text = $huge_text . "abc" . "bcd";
    return 1;
}

1) Restart Apache
2) Start `top`
3) Request.
4) Apache eats ~4MB instead of 1....
I know that mod_perl(or may be perl) don't free memory of $huge_string 
because most likely it will be needed in next call, but also it take 
another MBs for concatenation. Why?
Above example uses ~4MB of memory and until child restart apache don't 
free memory.

But if I want to prevent huge memory usage I can add undef($huge_text); 
just before return, but undef force freeing of only 1MB. ~3MB leaks and 
make me use MaxRequestsPerChild... :(

It's an hypothetical example, but now we use huge system(RT from Best 
Practical) and without limiting requests per child we fall in apache 
lock down.

How to debug this situations. I want to find way how to change some 
calls that allow perl don't allocate additional memory. I'm looking for 
approaches of debuging such leaks.

        Best regards. Ruslan.

Re: [MP1] Memory usage(eating, leaking)

[Perrin Harkins <pe...@elem.com>]

On Thu, 2003-09-25 at 05:36, Ruslan U. Zakirov wrote:
> I'm looking for suggestions, information, may be atricles about 
> different memory usage issues concerned with mod_perl1.

The best information about this kind of tuning is at
http://perl.apache.org/ and in the book "Practical mod_perl" from
O'Reilly.

> On one Russian forum man posted an review of memory "leaks"(caveats):
> 
> sub handler
> {
>         my $r = shift;
>         $r->send_http_header('text/plain');
>         print "Hello, World!\n";
>         print ttt();
>         return OK;
> }
> sub ttt
> {
>     my $huge_text = 'x' x 1000000;
>     my $huge_text = $huge_text . "abc" . "bcd";
>     return 1;
> }
> 
> 1) Restart Apache
> 2) Start `top`
> 3) Request.
> 4) Apache eats ~4MB instead of 1....

When I run this (with a few changes to make it a valid module), my
apache uses 3784K of memory total, and more than half of that is shared,
leaving only 1620K per child actually being used.  It doesn't grow if I
keep hitting the same handler over and over.  There is no leak.

> I know that mod_perl(or may be perl) don't free memory of $huge_string 
> because most likely it will be needed in next call, but also it take 
> another MBs for concatenation. Why?

It's just a matter of how Perl does the concatenation.  When you write
it this way, it creates a temporary string and uses more memory.  It
doesn't take the additional memory if you do it like this instead:

  $huge_text .= "abc" . "bcd";

You can see the same effect in a command-line Perl program.

> But if I want to prevent huge memory usage I can add undef($huge_text); 
> just before return, but undef force freeing of only 1MB. ~3MB leaks and 
> make me use MaxRequestsPerChild... :(

It's not really leaking (it doesn't grow).  You can't undef the
temporary string you created because you have no name to reference it
by.

> It's an hypothetical example, but now we use huge system(RT from Best 
> Practical) and without limiting requests per child we fall in apache 
> lock down.

I don't know enough about RT to comment on it, but it's a mistake to run
any mod_perl system without Apache::SizeLimit (or Apache::GTopLimit)
enabled.

- Perrin

Re: [MP1] Memory usage(eating, leaking)

[Mark Hawkes <ha...@onetel.net.uk>]

At 13:36 2003-09-25 +0400, you wrote:
>        Hi, all.
>I'm looking for suggestions, information, may be atricles about different 
>memory usage issues concerned with mod_perl1.

Hi there,
This contains some pretty good tips...

         Code Profiling and Memory Measurement Techniques
         http://www.apacheweek.com/features/mod_perl10

Mark