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From Brantley Hobbs <sbho...@uga.edu>
Subject Re: Keeping busy site responsive
Date Wed, 27 Jun 2007 17:37:23 GMT
Clinton,

I implemented this as a filter/listener combination.

The listener tracks session initialized events and increments an atomic 
Integer (decrementing it at session destroyed), saving it as a context 
attribute.

The filter uses the following logic:

1.  If we're less than or equal to the number of allowed sessions, allow 
this one through.
2.  If we've exceeded the limit, check to see if this user already has 
an established session (using the request's getSession(false) call).  If 
they have an established session, allow them through.
3.  If they don't match either of the above, send them a redirect to a 
page letting them know to try back later.

This approach seems to work well (at least until the box staggers to a 
halt simply issuing redirects).  I've hit a box with numbers that are at 
least double what the limit is and the people that have established 
sessions don't notice a thing.  Because it's simple filters and 
listeners, it should be fairly portable. I've attached the source with 
this mail.  There might be a couple of dependancies you can get rid of 
(like our log manager class), but it should be pretty easy to drop in.

Hope this helps.

B.

Parham, Clinton wrote:
> Tomcat Experts:
>
> How do I keep my web application responsive for users already half way
> through an enrollment process when traffic volume is high?
>
> Here's the scenario: I have a set of 5 web pages that users must work
> through to successfully enroll themselves. Assume the server can handle
> 250 concurrent requests (maxThreads). While traffic volume is under 250,
> enrollments complete normally. But once volume exceeds 250 and saturates
> the acceptCount/backlog queue, users half way through enrollments cannot
> complete their enrollment (connections are refused) because new users
> keep bombarding the site.
>
> What would be acceptable is for new users to see a 'site is busy
> message' while enrollments in progress are completed. As enrollments
> complete and concurrent threads drop below 250, new users are allowed
> through.
>
> I have already considered maxActiveSessions but I don't think this will
> solve the problem. If maxThreads is reached and the acceptCount/backlog
> queue is exhausted, then the users with active sessions and already
> partly through enrollment won't be able to get back in to the site to
> complete their enrollment - right?
>
> Adding more servers to handle the load is not preferred because most of
> the time they will be underutilized. Enrollments that experience high
> traffic don't happen that often but when they do, we need to support
> them.
>
> Thank you for your time.
>
>
>
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