Apache::Status and Measuring Code Memory Usage (Practical mod

9.4. Apache::Status and Measuring Code Memory Usage

The Apache::Status module allows you to peek inside the Perl interpreter in the Apache web server. You can watch the status of the Perl interpreter: what modules and Registry scripts are compiled in, the content of variables, the sizes of the subroutines, and more.

To configure this module you should add the following section to your httpd.conf file:

<Location /perl-status>
    SetHandler perl-script
    PerlHandler +Apache::Status
</Location>

and restart Apache.

Now when you access the location https://localhost:8000/perl-status you will see a menu (shown in Figure 9-1) that leads you into various sections that will allow you to explore the innards of the Perl interpreter.

Figure 9-1. Main menu for Apache::Status

When you use this module for debugging, it's best to run the web server in single-server mode (httpd -X). If you don't you can get confused, because various child processes might show different information. It's simpler to work with a single process.

To enable the Apache::Status modules to present more exotic information, make sure that the following modules are installed: Data::Dumper, Apache::Peek, Devel::Peek, B::LexInfo, B::Deparse, B::Terse, and B::TerseSize. Some of these modules are bundled with Perl; others should be installed by hand.

When you have the aforementioned modules installed, add these directives to your httpd.conf file:

PerlSetVar StatusOptionsAll On
PerlSetVar StatusDumper On
PerlSetVar StatusPeek On
PerlSetVar StatusLexInfo On
PerlSetVar StatusDeparse On
PerlSetVar StatusDeparseOptions "-p -sC"
PerlSetVar StatusTerse On
PerlSetVar StatusTerseSize On
PerlSetVar StatusTerseSizeMainSummary On

and restart Apache. Alternatively, if you enable all the options, you can use the option StatusOptionsAll to replace all the options that can be On or Off, so you end up with just these two lines:

PerlSetVar StatusOptionsAll On
PerlSetVar StatusDeparseOptions "-p -sC"

When you explore the contents of the compiled Perl module or Registry script, at the bottom of the screen you will see a Memory Usage link. When you click on it, you will be presented with a list of funtions in the package. For each function, the size and the number of OP codes will be shown.

For example, let's create a module that prints the contents of the %ENV hash. This module is shown in Example 9-6.

Example 9-6. Book/DumpEnv.pm

package Book::DumpEnv;
use strict;
use Apache::Constants qw(:common);
sub handler {
    shift->send_http_header('text/plain');
    print map {"$_ => $ENV{$_}\n"} keys %ENV;
    return OK;
}
1;

Now add the following to httpd.conf:

<Location /dumpenv>
    SetHandler perl-script
    PerlHandler +Book::DumpEnv
</Location>

Restart the server in single-server mode (httpd -X), request the URL https://localhost:8000/dumpenv, and you will see that the contents of %ENV are displayed.

Now it's time to peek inside the Book::DumpEnv package inside the Perl interpreter. Issue the request to https://localhost:8000/perl-status, click on the "Loaded Modules" menu item, and locate Book::DumpEnv on the displayed page. Click on it to request a page at the URI https://localhost:8000/perl-status?Book::DumpEnv. You will see the screen shown in Figure 9-2.