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RE: Improper Load Balancing

From: Freeman, Donald <>
Date: Thu, 22 Mar 2007 11:16:58 -0400
Message-ID: <51327ABA927BEF4B96590554CEA7832C060B993F@enhbgpri05.backup>

We are using all Microsoft drivers at this point so we don't have much control at our end.

From: Nigel Thomas [] Sent: Thursday, March 22, 2007 11:03 AM
To:; oracle-l
Subject: Re: Improper Load Balancing


It may not be relevant in your environment, but we had similar problems in a three tier system (OC4J webserver, OC4J app server, RAC database, 9iR2). The problem was that all app server nodes had the same configuration - so they all tended to connect their first N sessions
(the session pool minimum) to the same node. You could be seeing the
same thing; web clients are nicely load balanced, but the web-to-DB connection isn't. When the session pool is created, there's no load on the RDBMS - so a connection storm (like server startup) tends to hit one node - load metrics are only updated slowly (after a few seconds at least) - so SQL*Net load balancing just isn't suitable (at least at 9iR2 RAC) for session pools; you have to help it along.  

More background on what we did to work around this and a related problem
(if you are interested) here: s-in.html  

Regards Nigel

We are experiencing problems with the database connectivity from the production web servers for the last 2-3 weeks. We are using Oracle RAC in the production and there are 2 database servers. Somehow the connection goes to one database server intermittently, not all the time. But when it happens we see most of the connections going to the same Oracle node i.e. second node. We are using Windows load balancing on the web servers. Does anybody have any idea what might cause this?

Don Freeman
Database Administrator 1
Bureau of Information Technology
Pennsylvania Department of Health
(717) 703-5782

Received on Thu Mar 22 2007 - 10:16:58 CDT

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