for my $db (keys %{$db_ds}) {
  ...figure out which table to dump, etc...
  unless (defined(my $pid = fork)) {
    die "unable to fork: $!\n";
  }
  if ($pid == 0) {
    exec("$cmd > $dumpfile");
    die "unable to exec for table $table: $!\n";
  }
}

# now wait for all the children to finish

1 while (wait > 0);