kernel option HZ and mysql

[Chad Leigh -- Shire.Net LLC]

I have a self-compiled mysql 4.1 (4.1.9) on FreeBSD 5.3.  (Not built 
from ports for various reasons).  The system load skyrockets when the 
web server that is using the mysql for its PHPnuke storage starts to 
get 100 or so or more active sessions.  It appears that mysql is the 
"culprit."  The webserver is a prefork apache 2 with php5 and runs on 
the same system.  top and other monitors show very little cpu on the 
httpd processes but lots on the mysql.

There is plenty of free and inactive RAM and the CPUs are not 
particularly stresses (dual Opteron 2.0ghz in i386 mode).

I am thinking that maybe the HZ setting could be causing some 
inefficiencies for mysql.

It is set at  HZ=1300

mysql itself was compiled with

$ ./configure --prefix=/usr/public/mysql/mysql4.1 --enable-assembler 
--enable-thread-safe-client --without-debug 
--with-extra-charsets=complex

and it uses

 > ldd mysqld
mysqld:
         libz.so.2 => /lib/libz.so.2 (0x283c2000)
         libcrypt.so.2 => /lib/libcrypt.so.2 (0x283d2000)
         libpthread.so.1 => /usr/lib/libpthread.so.1 (0x283ea000)
         libstdc++.so.4 => /usr/lib/libstdc++.so.4 (0x2840e000)
         libm.so.3 => /lib/libm.so.3 (0x284e0000)
         libc.so.5 => /lib/libc.so.5 (0x284fa000)
 >


I would appreciate it if someone who has experience in this with mysql 
and HZ and HZ in general could comment on how HZ might affect mysql 
performance and system load.

Thanks
Chad