Question

I’m having some memory leak issues in a perl script that I’m running for extended periods of time, where the amount of memory that perl is taking up just continues to grow. Because of this, I am trying to use Devel::Leak to track down the leak. I discovered that whenever I call DBI‘s prepare method, the number of scalar values returned by Devel::Leak goes up by one. Below is I test script I’ve put together that does what I’m describing:

#!/usr/bin/perl
use strict;
use Devel::Leak;
use DBI;

START:
my $handle; # apparently this doesn't need to be anything at all
my $leaveCount = 0;
my $enterCount = Devel::Leak::NoteSV($handle);
print "ENTER: $enterCount SVs\n";
{
    # CONFIG VARIABLES
    my $platform = "mysql";
    my $database = "db";
    my $host = "localhost";
    my $port = "3306";
    my $user = "user";
    my $pw = "pass";

    #DATA SOURCE NAME
    my $dsn = "dbi:mysql:$database:$host:3306";

    # PERL DBI CONNECT
    my $dbh = DBI->connect($dsn, $user, $pw);
    $dbh->prepare("SELECT * FROM table"); # The script seems to gain one SV without this
                                          # line here, but since this is my issue in my
                                          # main script I decided to leave it in
    # undef $dbh; I tried undef-ing this, but it made no difference
}
$leaveCount = Devel::Leak::CheckSV($handle);
print "\nLEAVE: $leaveCount SVs\n";
sleep(1);
goto START;

So is there something I’m doing wrong here, or is this a memory leak in the DBI module? Also, I know that adding one SV every time around the loop isn’t a huge deal, and that I most likely have larger memory leaks elsewhere that are causing perl to take so much of the server’s memory. However, I’d still like to fix this if I could. Coder’s curiosity 🙂

UPDATE:

The first time through it seems to add about 3,000 SV’s, and then every time after that it goes up 1 at a time.

Answer 1

There is a instance of DBI::dr (a blessed hash) living at $DBI::lasth. Check out the ChildHandles key.

#!/usr/bin/perl

use strict;
use warnings;
use Devel::Leak;
use Data::Dumper;
use Symbol::Table;
use DBI;

START:
{
    my $handle;
    my $enterCount = Devel::Leak::NoteSV($handle);

    DB:
    {
        my $platform = "mysql";
        my $database = "db";
        my $host     = "localhost";
        my $port     = "3306";
        my $user     = "user";
        my $pw       = "pass";

        my $dsn = "dbi:mysql:$database:$host:3306";

        my $dbh = DBI->connect( $dsn, $user, $pw );

        $dbh->prepare("SELECT * FROM table");

        $dbh->disconnect();
    }

    my $st = Symbol::Table->New( 'SCALAR', 'DBI' );

    for my $subpkg ( keys %{ $st } ) {

        my $val;
        {
            my $var = "DBI::${subpkg}";
            no strict 'refs';
            $val = ${$var};
        }

        print "scalar '$subpkg' => '$val'\n";
    }

    print Dumper( $DBI::lasth );

    $DBI::lasth->{ChildHandles} = []; # <-- reset leaking data structure

    my $leaveCount = Devel::Leak::CheckSV($handle);

    print "\nCOUNT: $enterCount to $leaveCount SVs\n";

    sleep(1);

    redo START;
}