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Session monitoring in WebLogic

Posted on 2009-07-12
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What is the difference between Sessions, Sessions High and Total Sessions? These are the column headings in WLS 9 and 10 versions. The definition of these as given in edocs is simple however when I load tested a web app using session replication in a cluster of few managed servers the session data that I observed was quite ambiguous when compared to the definitions:
Sessions: Specifies the number of sessions that are currently active in the Application.
Sessions High: Refers to the highest number of concurrent sessions that were open for an Application.
Total Sessions: Refers to the total number of sessions that were opened since deployment of an Application.

Session data:
Server: Sessions/ Sessions High/Total Sessions
MS1: 590/550/548
MS2: 598/558/555
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Question by:pirabid
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rajesh_bala earned 2000 total points
ID: 24838269
This is the understanding. Do let me know if it is not clear.

Every session will have a starting time and a timeout value. It is not necessary that if we have 500 sessions, all 500 users are hitting the application.

Ex: User might have a shopping cart and server creates a session for him. It is not necessary that the user is continuously accessing the system. He might go for a break and come back, add some more to his cart. But till then the session is kept alive based on the timeout setting.

Now, that being said...

Sessions: It specifies the number of LIVE sessions present in application server at that point of time. It does not give any information about concurrent users.

Sessions High: This is used for measuring the blips in the server. Assume you have high traffic for 2 hours in a day. Only during that time your sessions might reach 1000. Rest of the time, it might be 80 (I am just giving an example here). So sessions high is used for measuring the peak load on that server.

Total Sessions: This is a cumulative figure which gives the total number of sessions created after starting the application. You can relate it to site statistic details (unique user statistics given in most site using javascript or so).
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by:rajesh_bala
rajesh_bala earned 2000 total points
ID: 24838283
But in your case, the counters are misleading. Ideally I would have expected > 590 for "TOTAL-SESSIONS" in MS1.

However, for monitoring purpose I would bother about the following.

Sessions - Gives an understanding of memory requirements for JVM. If there are 10000 sessions and each of them occupy 5kb data, then you might end up requiring lots of memory. So this figure gives an understanding of the memory requirements and to understand if you really need to tune session-timeout.

Session High - Ideally these blips can be monitored in webserver logs itself. So I would tend to rely on them better.
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Author Comment

by:pirabid
ID: 24870672
This  is my latest observation and it may have something to do with the numbers that show up in the monitoring tab for sessions:

I was just browsing through the filesystem and saw that there was some session data in the persistent store directory that has not been deleted yet.  Maybe when servers startup next time they will take into account these sessions that have not been deleted somehow in past.

The servers are not running as of now. So, I'll be carrying out a test on dev machine  this week to check whether these sessions account for ambiguous numbers.
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