Hi all,

a process checking DNS names unexpectedly has eaten 12GB of memory, forced swapping and ringing almost all alarm bells of system monitoring.

So I was really surprised. DBI needed 1GB to get all results from the MySQL database into the process. That was expected for some millions of rows and ok. But afterwards I wanted to check the DNS name in a fetching loop. The used process memory grew and grew what I really didn't expect in this way.

Now I reduced the whole thing to the following snippet which is more or less literally taken from the man page of Net::DNS. Combined with the very usful package Test::LeakTrace I have the following:

#!/bin/env perl
use strict;
use warnings;
use strict;
use 5.010;

use local::lib './lib';
use Net::DNS;
use Test::LeakTrace;

die("ERROR: Please provide Loop count > 0 as first argument") unless $
+ARGV[0];

leaktrace {
    for (1..$ARGV[0]) {
        my $res = Net::DNS::Resolver->new;
        my  @mx = mx($res, "example.com");
    }
} ;
[download]

The result is that Test::LeakTrace reports MANY leaks. Following the documentation of Test::LeakTrace I gave Net::DNS a chance in a way that one-shot-costs are ok but iterating over meanwhile instantiated/cached code should not need additional memory. To prove this I have a for-loop around it which can be given on the command line. Together with the following little shell script:

for iterations in 1 2 3 4 5 6 7 8 9 10; do  perl  script.pl $iteration
+s 2>&1 | wc -l; done
[download]

I get the following output:

1374
1492
1612
1736
1859
1982
2106
2229
2353
2477
[download]

You see that the leaked memory rises with the itaration count. This seems to me very bad.

Now to you monks: I would be intersted to see the result on different plattforms with different Perl versions. If you have time and pleasure to test it on your Perl I would be really interested in the results.

By the way: If someone knows a package for DNS lookups not easting the memory of my machine should tell it. :-) Does anybody know some documentation how to read the verbose output of Test::LeakTrace (which is not used in this script)?

Thank you in advance

Regards
McA