I have a long-running Web app running under Perl 5.16.0 that processes hundreds of requests per minute and sadly leaks RAM ... very slowly, maybe 10-20 MB per day. I was able to figure out more major memory leaks in the past using the following code (which is set to run once per minute in the main event loop): 
if (!%first_arena) {
    %first_arena = %{arena_ref_counts()};
    
    my $all = Devel::Gladiator::walk_arena();
    for my $it (@$all) {
        if (ref $it eq 'ARRAY') {
            $arrays{refaddr($it)} = time();
        }
    }
    $all = undef;
} else {
    my %current_arena = %{arena_ref_counts()};
    my %increase;
    for my $type (keys %current_arena) {
        if (!exists $first_arena{$type}) {
            $increase{$type} = $current_arena{$type};
        } elsif ($current_arena{$type} - $first_arena{$type} > 2) {
            $increase{$type} = $current_arena{$type} - $first_arena{$t
+ype};
        }
    }
    if (%increase) {
        print "\nincreases\n";
        for my $type (sort { $increase{$b} <=> $increase{$a} } keys %i
+ncrease) {
            print "$increase{$type}\t$type\n";
        }
        print '%client: '.(scalar keys %client)."\n";
        print '%comet: '.(scalar keys %comet)."\n";
        print '@ready: '.(scalar @ready)."\n";
        print '%async: '.(scalar keys %async)."\n";

        my %leaked_arrays;
        my $all = Devel::Gladiator::walk_arena();
        for my $it (@$all) {
            if (ref $it eq 'ARRAY' and !exists $arrays{refaddr($it)} a
+nd ++$array_count{refaddr($it)}{md5_hex(Dumper $it)} >= 3) {
                $leaked_arrays{refaddr($it)} = $it;
            }
        }
        $all = undef;
        if (%leaked_arrays) {
            my $zero_length = scalar grep { scalar @{$leaked_arrays{$_
+}} == 0 } keys %leaked_arrays;
            my $non_zero_length = scalar grep { scalar @{$leaked_array
+s{$_}} > 0 } keys %leaked_arrays;
            print "leaked arrays: $zero_length zero length, $non_zero_
+length non zero length\n";
        }
    }
}

[download]
After a half hour or so, this prints: 
increases
24202   SCALAR
7482    REF
5966    HASH
5911    REF-HASH
4387    ARRAY
592     REF-SCALAR
552     REF-DBI::st
368     REF-DBI::db
368     DBI::st
184     DBD::Pg::st_mem
155     GLOB
74      CODE
57      REF-IO::Socket::INET
30      IO::File
29      IO::Socket::INET
22      REGEXP
%client: 28
%comet: 28
@ready: 0
%async: 0
leaked arrays: 3830 zero length, 156 non zero length

[download]
The only real leaks are the ARRAYs. Growth of non zero length ARRAYs is almost flat, but zero length ones grow at an average rate of 120 per minute! Why does it think it needs so many zero length ARRAYs?!

Does anyone know what kind of practices could cause this bizarre behavior? Or maybe some other tools I could use to find the source of the leak? A way to tell the line on which the zero-length ARRAYs were allocated would be perfect. I know about Devel::LeakTrace::Fast, but it requires a perl built for debugging, doesn't it? I can do that if I need to, but ...

Thank you, monks!

In reply to Leaking 0-length ARRAYs!? by njahnke

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