[Zope] Zope scalability / efficiency question

[J Cameron Cooper]

mark hellewell wrote:
> Hi everyone, I've got a question I'd really appreciate some input on.
> 
> If I'm running perhaps a dozen Zope sites, experiencing anywhere
> between several hits per second to a lot less, would it potentially
> be more efficient (decreased latency etc.) to run each site as its own
> Zope instance or have one Zope instance running muliple (CMF based)
> sites.
> 
> I haven't even thought about adding ZEO into the mix yet.
> 
> The basic aim of the exercise is to find out how many usable
> zope instances / sites I could get onto a typical mid-range 
> modern server.
> 
> I know it's a bit of a "how long are your pieces of string" sort
> of question, but any help you could offer would be gratefully
> accepted! If anyway has any experience of this sort of setup
> and can offer a little insight it might reduce the amount of
> testing I have to do myself.

I don't think you'll see any improvement unless you have a 
multi-processor machine. In such a case, running X processes (where C is 
the number of cores) will fully load the machine, since Python threads 
won't skip processors.

On a single-core machine, multiple instances probably will just increase 
your overhead, especially in memory. But I could be wrong: there's so 
many variables the best way to know is to test. (Caches and usage 
patters, for instance, can make a big difference.)

If you do have several sites, you could be running into cache eviction 
issues since there are a lot of objects that need to be accessed. Check 
your cache fullness and watch your ZODB usage chart for excessive loads.

		--jcc
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