[Zope] Scaling problems, or something else?

[Gaute Amundsen]

On Wednesday 16 May 2007 00:13, Paul Winkler wrote:
> On Tue, May 15, 2007 at 12:00:52PM +0200, Gaute Amundsen wrote:
> > I set cache-size to 10000 last night, up from the default.
> > I felt I had to try that before I had a grap in place, so I don't have
> > good numbers to estimate tha change, but with about 20 hits a sec on
> > apache, there was close to 500000 loads the last hour, and just 3000
> > writes.
> > Does that look reasonable?
>
> Not really. Too many loads; you're getting a lot of cache misses and
> blowing out the cache a lot. Keep on doubling the cache size until
> your whole working set is in RAM all the time.
>
Will do! 

> > The built in help seems to indicate I should increase the cache until
> > reads approaches zero..?
>
> Yeah, for some definition of "approaches".  I think a more realistic
> minimum would be number of threads * number of ZODB writes (since each
> write potentially invalidates one cached object per thread).
>
That would give me 2500*6 = 15000. Looks like a reasonable goal.

> It's hard to quantify the point at which you're caching enough, but
> you're not even close.
>
I can see from the config that we tried cache-size 20000 once, but probably 
set it back since something else was probably the problem that time :-(

> > > Also, I don't think you've mentioned what sort of app this is.
> > > Is it mostly reads or are there lots of writes?
> > > "Mostly reads" is a lot easier to optimize :)
> >
> > Big CMS system with about 70 virtual domains.
>
I keep mixing up the numbers here I notice, but make that ~180 hosts in apache 
and ~85 in zope.

> Based on your activity graph, you do indeed have a lot more reads than
> writes.
>
> What's the CMS based on? Plone? Silva?

Nothing of the sort. I'ts a "innhouse" thing...
Could be lots of gremlins burried there I know :-/

> Chris W. had a good point about the catalog.
>
> Do you have blobby data in the ZODB? (large images or files)?  Those
> tend to play havoc with zodb cache activity, since one OFS.Image is
> stored as an arbitrarily long chain of small persistent objects.  So
> whereas a Plone Document or a Page Template needs only one entry in
> the cache, an Image might need hundreds.
>
Not _that_ much. There is some from olden times, but we moved all our image 
stuff over into something based on phpgallery 2 years ago.

thanks :)

Gaute