Problem with Secondary systems with many zones

[Steven Job]

Quoting Sebastian Castro Avila <secastro at nic.cl>:
>
> Only to give you a number, we handle 43K zones using  BIND 9.
> Probably the zone number is not the problem. May be you should tune some
> parameters of the config file to handle the large number of zone
> transfers, for example.
>

Here is the config... Any suggestions?

options {
        version "The best version... What do you expect.";
        directory "/var/named";
        pid-file "/var/named/named.pid";
        recursion no;
        allow-query { any; };
        allow-transfer { "secdns";};
        // These people are banned from everything
        blackhole { none; };
        provide-ixfr yes;
        request-ixfr yes;
        transfers-per-ns 1000;
        transfers-out 2000;
};