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The moose likes OO, Patterns, UML and Refactoring and the fly likes Session Replication Big Moose Saloon
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Session Replication

Thomas Becker
Greenhorn

Joined: Mar 29, 2005
Posts: 23
Hi Cliff,

What do you think about Session Replication? Is it the pure headache as I know it or is it worth to put tons of work to get Session Replication to work as it should.

I worked as a Applications Operations Specialist for big webapplications. They were supposed to replicate their sessions to avoid any outage for the customers during restarts/outages/so on. It sometimes worked and usually put other unwanted side-effects to the portal.

I'm interested in your opinion.

Cheers,
Thomas
[ January 17, 2006: Message edited by: Ilja Preuss ]
Stan James
(instanceof Sidekick)
Ranch Hand

Joined: Jan 29, 2003
Posts: 8791
We use WebSphere session persistence to UDB. Is that the kind of thing you mean? We had a rough start because our vendor framework put some VERY large objects on the session. Since we got rid of those it works fine. We can stop and restart one sick node in the cluster with almost zero user impact.


A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi
Cliff Berg
Author
Greenhorn

Joined: Jan 16, 2006
Posts: 22
Hi Thomas,

One has to consider the risks and benefits. If a session is persistent, then it is possible to retain the session if a failover occurs. It is also possible for the user to rejoin their session if their app server fails and they failover to another server. These are valuable benefits. But a persistent session is inevitably more resource-intensive. I have seen it work well - even with a home-grown approach. On the other hand, since node failure is rare, it might be more cost-effective to simply restart the session. This would especially be true if the end user is not human (machine-to-machine) or if session content is minimal. If the session persistence mechanism is problem-ridden, it is almost certainly not worth it. I see no inherent reason why it should be problem-ridden though.

- Cliff
 
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subject: Session Replication