Bind9.5.1b1 Heavy CPU Load?

[iman]

I compiled and installed bind9.5.1b1 (without threads)on solaris 9 in
an ultrasparc machine with 2cpu`s 900 Mhz and 4G Ram.
unfortunately,after few hours,named process consumes heavy load from
cpu:
   PID USERNAME  SIZE   RSS STATE  PRI NICE      TIME  CPU PROCESS/
NLWP
  1064 root      109M  107M cpu2    59    0   2:23:45  93% named/5
then some queries responded and some queries dont respond.
Here are my named.conf:
options {
        version "version not currently available";
        pid-file "/opt/namesurfer/run/named.pid";
        directory "/opt/namesurfer/named/namedb";
        dump-file "/opt/namesurfer/named/namedb/named.dump";
        recursive-clients 65536;
        statistics-file "/opt/namesurfer/named/namedb/statistics";
        tcp-clients 32768;
       };
logging {
        channel simple_log {
                file "/var/adm/named/bind.log" versions 3 size 50m;
                print-category yes;
                print-severity yes;
                print-time yes;
                severity warning;
        };

        category d
efault {
                simple_log;
        };
};
controls {
        inet  127.0.0.1 port 953 allow { 127.0.0.1; } keys
{ "rndckey"; };
};

Does it relate to logging options?
i removed it from named.conf,,but bind sent logs to syslog and the cpu
problem existed?!(is this default for bind 9.5.x?how can we disabled
this default state?)
How can i solve this heavy cpu load problem?