[imp] single machine versus load balancing

[Eric Rostetter]

Quoting Charlie Reitsma <reitsmac at denison.edu>:

> setoolkit reports the CPU is overloaded (I'll see load average over 50
> sometimes). Users will experience a minute between clicks sometimes. The
> IMAP box rarely exceeds 50%. The high load is http clients.

Besides the usual tuning, consider a php accelerator.  It may help enough.
But probably you do need a faster box if you want real fast access times
during peak hours.
 
> Reading the scaling article on the horde site I get the feeling that
> there are sites handling my population size on a single box without
> problems.

Yes, I've done it, but on a dual cpu machine.  You will be slow with
a single 500Mhz cpu, IMHO.

> Should I consider load balancing with round-robin DNS or a

Simple RR DNS will probably result in session problems, unless you 
somehow share the sessions (should be possible since you say you use
sql for sessions).

> dual processor single box?

That would definately help.  I always run services like this on a multi-cpu
box so one user (process) can't slow down every one else.

> That is, do the advantages or disadvantages
> of either choice make one more desirable?

A real load balancing system would be good.  Round Robin won't help as 
much.  Another cpu will certainly help.
 
> If I were to go a single box I probably would go with a Sun LX50, dual
> processor, 1 Gig RAM running Solaris.

Sounds reasonable.  But I'd still look at using a php accelerator if you can.

> If I were to do load balancing I
> would continue to use Sun Netra X1 and look at load balancing hardware
> as well.

If you want to load balance, hardware is the way to go IMHO.  RR DNS just
isn't going to help during peak times, and won't help if one machine goes
off the air the way a good hardware load balancer will.

> TIA,
> Charlie

-- 
Eric Rostetter
The Department of Physics
The University of Texas at Austin

Why get even? Get odd!