Thanks for the pointer, I tried to follow the example as close as possible and came up with this (not proberly working) code:

sub metasearch {
    my $self = shift;
    my $db_ref = $self->db_defs;
    my @dbs = @{$self->dbs};
    my $logger = $self->logger;

    $SIG{CHLD} = 'IGNORE';
    my @result;
    foreach my $db (@dbs) {
        defined (my $kid = fork) or die "Cannot fork: $!\n";
        $logger->debug("Processing $db in process $kid");
        if ($kid) {
            $logger->debug("Parent $$ has finished, kid's PID: $kid");
        }
        else {
            # $r->cleanup_for_exec(); # untie the socket
            open STDIN, '/dev/null' or die "Can't read /dev/null: $!";
            open STDOUT, '>/dev/null' or die "Can't write to /dev/null
+: $!";
            open STDERR, '>/tmp/log' or die  "Can't write to /tmp/log:
+ $!";
            # setsid or die "Can't start a new session: $!";
            my $oldfh = select STDERR; local $| = 1; select $oldfh;
            warn "started\n";
            sleep 1, warn "$_\n" for 1..20;
            warn "completed\n";
            push @result, "simulate result for $db in $kid";
            CORE::exit(0); # terminate the process
        }
        $logger->debug("End of $db");
    }
    $logger->debug(join(', ', @result));
}
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The difference is a foreach around the forks and the attempt to collect some result from the forked processes in @result but @result is empty.

What am I doing wrong?

As a side-note since I am not really interested in the warn-output: /tmp/log is empty after the run. Does this indicate that the child(s) didn't run?

I left out the cleanup_for_exec and the setsid lines because from the explanation I gathered they are not necessary in my situation and I didn't know if cleanup_for_exec call is still the same in mod_perl2 (the example is for mod_perl1)