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Subject Re: Storing Tomcat Sessions to MySQL (and Memcached) Round-Robin without sticky sessions
Date Thu, 17 Dec 2009 22:28:38 GMT
> On 17/12/2009 20:24, wrote:
>>> Hi Mark, Thanks for the reply.
>>> In your opinion should we be using local memory to store any session
>>> data? The discussion right now is to store everything to cache+db and
>>> nothing in local memory.
>> The problem with any cache system is cache coherency. Tomcat takes the
>> easy way out by requiring that sessions be "sticky" to a single box, and
>> using local access management. Sticky session have well known
>> scalability
>> issues.
> 1. Please take this to the users list.

I didn't start this thread and am not sure how to do that.

> 2. You are making some strong statements here regarding the current
> implementation with little in the way of hard data to back up those
> statements. You might want to consider including some justification in
> future postings.

Problems with sticky sessions:

What happens to the sticky sessions when the a server crashes or is taken
out of service after peak load?

Load balancing on "sticky" servers tends to be less efficient because user
requests can't be sent to the "next least loaded" server, they have to be
sent to a particular server which may not be the least busy.

When you dynamically add servers to a server farm to manage load during
peak times, the "sticky" load does not get reduced unless you invalidate
the sessions and recreated them.

Sessions that reside solely on a specific server box are very limited. If
they are in a globally shared and managed environment, they can be used by
other systems.

That is just the ones off the top of my head.

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