use DBI;
use POE;

my $dbh = DBI->connect('dbi:mysql:****', '****', '****', {RaiseError => 1});

POE::Session->create(inline_states => {_start    => \&tester}, heap => {dbh => $dbh->clone()});
POE::Session->create(inline_states => {_start    => \&tester}, heap => {dbh => $dbh->clone()});

POE::Kernel->run();

sub tester {
    my $heap = $_[HEAP];
    for my $key (@{$heap->{dbh}->selectcol_arrayref("SELECT id, sleep(0.1) FROM mytable WHERE 1")}) {
        print $key;
    }
}

##</code><code>##

my @threads;
for my $i (1..2) {
  push @threads, threads->create(\&testsub, $dbh->clone());
}

foreach my $thread (@threads) {
    $thread->join();
}

sub testsub
{
  for my $key (@{$_[0]->selectcol_arrayref("SELECT id, sleep(0.1) FROM keywords WHERE 1")}) {
        print $key;
  }
}