my $dbh = DBI->connect(XXXX);
my $dbh_tx = DBI->connect(XXXX, AutoCommit => 0);

#  non-transactioned
runSomeQueries($dbh);
runSomeSubQueries($dbh);

#  if you need to transaction a bunch of queries together
runSomeQueries($dbh_tx);
runSomeSubQueries($dbh_tx);
if ( $OK )
{
    $dbh->commit();
}
else
{
    $dbh->rollback();
}