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From Lists <li...@dankeeley.co.uk>
Subject Re: CPU usage quirk with multiple tomcat instances
Date Tue, 06 May 2008 08:29:49 GMT
Yes, same webapp load - i.e. they're both handling the same number of
transactions per second.

I guess the only advantage of multiple JVM's is reliability - if one
instance goes down the other can still handle load on that machine.

Also; I guess someone thought originally that 2 instances doing less work
would be easier for the VM to handle and therefore more performant than one
instance doing it all - clearly not!  ( I didnt set this architecture up -
If it's best practice to use one VM on each app server then fair enough -
i'd like to read up why tho! )

Thanks!
Dan

--------- Original Message --------
From: Tomcat Users List <users@tomcat.apache.org>
To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: CPU usage quirk with multiple tomcat instances
Date: 04/05/08 12:49

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Da,
> 
> Lists wrote:
> |&gt; My guess (and that's all it is) is that you have eliminated much of
the
> |&gt; context-switching overhead that two instances would have compared to
one.
> |
> | Ah I see.  I guess i can look at that with mpstat and look at things
like
> | thread migrations etc.  Important because if we install more CPU's i
guess
> | that may mitigate the context switching overhead.  Or maybe we can gain
> | performance by tying zones to one or two cpu's.
> 
> Is there any advantage to running multiple JVMs on a single machine? Why
> not just give your single JVM a big chunk of memory and let it do its
thing?
> 
> | Opteron 254 vs 252.  So 0.2ghz less but afaik no other difference.  Not
> | enough of a difference to account for the additional cpu.  so this box
> uses
> | 80% cpu vs 30% on the other one for the same load.
> 
> Do you mean &quot;same webapp load&quot;? Obviously, that addition load is
coming
> from /somewhere/. What about other services running on the same machine?
> 
> - -chris
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