Memory leak in connect and undef

[Carlos Velasco]

Hello,

Debugging a long term perl daemon for memory leaks I have found out that
just a DB connect and undef leaks.

This simple code leaks:
===
#!/usr/bin/perl

use DBI;

my $con;

$con = DBI->connect('DBI:mysql:database=test;host=127.0.0.1', 'root',
'pass', {PrintError => 0,PrintWarn=>0});
undef $con;
===

I used Devel::Leak and opened a bug in DBD::mysql
http://bugs.mysql.com/bug.php?id=66859

But the problem seems to be in DBI.

Using Devel::leak::Object reveals leaking in DBI::var.

This code:
===
#!/usr/bin/perl

# Track every object including where they're created
use Devel::Leak::Object qw{ GLOBAL_bless };
$Devel::Leak::Object::TRACKSOURCELINES = 1;

use DBI;

my $con;

for (1..1000) {
$con = DBI->connect('DBI:mysql:database=test;host=127.0.0.1', 'root',
'pass', {PrintError => 0,PrintWarn=>0});
$con->disconnect();
undef $con;
}
===

Outputs:
===
Tracked objects by class:
Config 1
DBI::var 5

Sources of leaks:
Config
1 from /usr/lib64/perl5/5.16.1/x86_64-linux-thread-multi/Config.pm
line: 73
DBI::var
5 from
/usr/lib64/perl5/site_perl/5.16.1/x86_64-linux-thread-multi/DBI.pm line: 306
===

I used DBI-1.622_901 (latest version I saw), and line 306 is:
sub DBI::var::TIESCALAR{ my $var = $_[1]; bless \$var, 'DBI::var'; }

Don't know how to debug this further.

Perl is 5.16.1
DBD::mysql is 4.022
mysql is mysql-5.5.27.tar.gz


Also, it seems these leaks have been there from long time ago:
https://bugs.launchpad.net/ubuntu/+source/libdbd-mysql-perl/+bug/51746

Regards,
Carlos Velasco

[Carlos Velasco]

Hi,

I used another script (see below) making multiple connections and now I
see really strange results.

Running in a "standard" DBI, results shows some memory fluctuation:

# perl test6.pl
INIT count: 9116
PRE count: 12653
POST 100 count: 12754
POST 200 count: 12734
POST 300 count: 12714
POST 400 count: 12694
POST 500 count: 12674
POST 600 count: 12654 <-- near no leak
POST 700 count: 12754
POST 800 count: 12734
POST 900 count: 12714
POST 1000 count: 12694
POST 1100 count: 12674
POST 1200 count: 12654
POST 1300 count: 12754
POST 1400 count: 12734
POST 1500 count: 12714
POST 1600 count: 12694
POST 1700 count: 12674
POST 1800 count: 12654
POST 1900 count: 12754
POST 2000 count: 12734

However, recompiling DBI and disabling weak references, as Tim said here:
===
#ifdef sv_rvweaken
if (1) {

Change the 1 to a 0 to disable the use of weakrefs which was added in 1.49.
===
http://coding.derkeiler.com/Archive/Perl/perl.dbi.users/2006-07/msg00076.html

Shows no leaks at all:
# perl test6.pl
INIT count: 9116
PRE count: 12650
POST 100 count: 12651
POST 200 count: 12651
POST 300 count: 12651
POST 400 count: 12651
POST 500 count: 12651
POST 600 count: 12651
POST 700 count: 12651
POST 800 count: 12651
POST 900 count: 12651
POST 1000 count: 12651
POST 1100 count: 12651
POST 1200 count: 12651
POST 1300 count: 12651
POST 1400 count: 12651
POST 1500 count: 12651
POST 1600 count: 12651
POST 1700 count: 12651
POST 1800 count: 12651
POST 1900 count: 12651
POST 2000 count: 12651


So I am really confused, is this a bug in the weak references code? or
is this a buffer, cache or similar? Is this working as designed?


Test script:
===
#!/usr/bin/perl

use Devel::Leak;

use DBI;

my $DLcount;
my $DLhandle;

my $i = 0;
my $con;

$DLcount = Devel::Leak::NoteSV($DLhandle);
print "INIT count: $DLcount\n";

$con = DBI->connect('DBI:mysql:database=test;host=127.0.0.1', 'root',

'', {PrintError => 0,PrintWarn=>0});
undef $con;

$DLcount = Devel::Leak::NoteSV($DLhandle);
print "PRE count: $DLcount\n";

for (1..20) {
for (1..100) {

$con = DBI->connect('DBI:mysql:database=test;host=127.0.0.1',

'root', '', {PrintError => 0,PrintWarn=>0});
undef $con;
$i++;
}

$DLcount = Devel::Leak::NoteSV($DLhandle);
print "POST $i count: $DLcount\n";
}
===