eval {
  my $dbh = DBI->connect(..., {RaiseError=>1});
  eval {
    $dbh->do("update ...");
    $dbh->do("update ...");
  };
  if ($@) {
    # clean up after an unsuccessful update
    $dbh->rollback();
    $dbh->disconnect();
    die($@);  # reraise the error
  }
  # successful update
  $dbh->commit();
  $dbh->disconnect();
};
if ($@) {
  log($@);
}