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From "Len Popp" <len.p...@gmail.com>
Subject Re: Are Sticky Sessions really necessary?
Date Sat, 03 Nov 2007 15:16:23 GMT
But isn't the purpose of session replication to allow different
servers to handle the session? If not, what's it for?
-- 
Len

On 11/3/07, Peter Rossbach <pr@objektpark.de> wrote:
> Hi,
>
> It is not only ineffizient and a risk, Read 7.7.2 at the spec:
>
> SRV.7.7.2 Distributed Environments
> Within an application marked as distributable, all requests that are
> part of a session
> must be handled by one Java Virtual Machine1 ("JVM") at a time. The
> container
> must be able to handle all objects placed into instances of the
> HttpSession class
> using the setAttribute or putValue methods appropriately.
> ....
>
> regards
> Peter
>
> Am 02.11.2007 um 22:37 schrieb Len Popp:
>
> > You can indeed use session replication without sticky sessions, and
> > the session data will be copied to all the Tomcat servers. However it
> > may be inefficient. You probably have to use synchronous replication
> > to ensure the session data is consistent across the cluster, which
> > adds latency to the requests. And there could be a lot of extra
> > network traffic in the cluster if it's busy (which it is, otherwise
> > you wouldn't be doing load balancing).
> >
> > (I haven't used session replication in a high-load situation. Maybe
> > someone else can tell us how well it works.)
> > --
> > Len
> >
> > On 11/2/07, Stephen Wick <swick@nicholsonkovac.com> wrote:
> >> The Tomcat 5.5 "Clustering/Session Replication Guide" says, "Make
> >> sure
> >> that your loadbalancer is configured for sticky session mode."
> >> However,
> >> I don't see the term "Sticky" sessions anywhere in the Servlet 2.3 or
> >> 2.4 specifications.
> >>
> >> Are sticky sessions really required for clustering to function
> >> properly
> >> in Tomcat 5.5?  I thought that session replication would eliminate
> >> any
> >> need to direct a client session to one node in a cluster.
> >>
> >> If not, can we adjust the documentation to indicate that Sticky
> >> sessions
> >> are optional, for the appropriate reason (I'm guessing the advent of
> >> session replication in tomcat.)
> >>
> >> I am asking this question because I am having trouble with Sticky
> >> sessions in my load balancer, and I need to know whether or not I
> >> should
> >> pursue fixing this feature.  If tomcat doesn't really require sticky
> >> sessions, then I can leave my load balancer alone.  If tomcat does
> >> need
> >> the feature to function properly, then I need to go to some
> >> additional
> >> expense to resolve the issue with my load balancing appliance.
> >>
> >> Thank you for your time and expertise.
> >>
> >> Stephen Wick
> >> Interactive Developer
> >> Nicholson Kovac, Inc.
> >>
> >> References
> >> http://tomcat.apache.org/tomcat-5.5-doc/cluster-howto.html
> >>
> >
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> >
>
>
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