[Building Sakai] More tomcats or bigger tomcats?

[Earle Nietzel]

I think the answers to this question are going to vary!

We started with a 32 bit jvm on a hardware with 4GB of memory where the 
maximum memory per process was 3GB. Sizing the jvm for that took some time 
to get it right. 

After switching to 64 bit hardware all the sizing issues were no more and 
testing small jvm heaps to large jvm heaps the large jvm heaps out 
performed the small heaps when more users were added. 

After monitoring sakai for some time my opinion is that processor usage is 
relatively low but memory usage is much more important and the more memory 
you have the more users you will be able to accomodate. The real 
bottleneck I have come to see is the database. The more users and tomcats 
you add the more activity your database will see. Your database will 
easily become the bottleneck far before your tomcats will. 

At Marist we choose to go with few tomcats with large jvms as this IMHO 
makes better use of cache thereby easing the strain on the database than 
having many small tomcats all with their own cache which generally means 
more queries for the database.

However it is clear that more testing of these types of scenarios 
(creating more tomcats with small jvm heaps equal to the same size of a 
single tomcat with a large jvm heap) will be helpful.

I look forward to hearing to them,

Earle



From:
John Bush <john.bush at rsmart.com>
To:
Joshua Swink <joshua.swink at gmail.com>
Cc:
Sakai-Dev <sakai-dev at collab.sakaiproject.org>
Date:
09/16/2009 11:04 PM
Subject:
Re: [Building Sakai] More tomcats or bigger tomcats?
Sent by:
sakai-dev-bounces at collab.sakaiproject.org



well, I don't have an answer for you, but I'm interested to know as 
well.  We are doing some performance testing right now and this is one 
of things I want to look at.  I think most people on 64 bit platforms 
are running heaps much bigger than 2 GB.  We are going to be looking 
at 1 8GB tomcat vs 2 4 GB tomcats, I don't think our current setup 
lets us look at anything bigger than that.  Hopefully I should have 
some results next week, I'll let you know what we figure out.

John Bush
Development Manager
rSmart




On Sep 16, 2009, at 11:59 AM, Joshua Swink wrote:

> Is it better to run more tomcat instances, sticking with the default 2
> GB heap size, or to run a single tomcat per CPU, using as much memory
> as can be allocated to each one?
>
> We currently run four tomcat instances on two machines, load balanced
> through Apache. Each one has the recommended 2 GB heap size.
>
> Our user load is always on the increase, and I was wondering what is
> the better configuration:
>
> - Increase the heap size on each tomcat's JVM? Perhaps to 3 GB.
> - Leave the heap size at 2 GB and run additional tomcat instances.
>
> Our current servers have 16 GB memory, so that works out to about 4-5
> tomcats per machine if we stay at 2 GB heap per instance. My main
> question is whether people have experienced better performance using
> more 2 GB tomcats, or fewer tomcats with larger heap sizes.
>
> Also, our servers have 2 CPUs each.
>
> Thanks for any advice!
>
> --
> Joshua Swink
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