BEGIN {
   package TransactionMaybe;

   sub begin {
      my ($class, $dbh) = @_;
      my $in_trans = eval { $dbh->begin_work() };
      return bless([$dbh, $in_trans], $class);
   }

   sub commit {
      my ($self) = @_;
      my  $dbh                       =   $self->[0];
      our $in_trans; local *in_trans = \($self->[1]);
      $dbh->commit() if $in_trans;
      $in_trans = 0;
   }

   sub DESTROY {
      my ($dbh, $in_trans) = @$self;
      local $@;
      eval { $dbh->rollback() } if $in_trans;
   }

   $INC{'TransactionMaybe.pm'} = 1;
}

{
   my $transaction = TransactionMaybe->begin($dbh);
   code_that_touches_db();
   $transaction->commit();
}