Sessions problem in a 3-tier application

Question

Dear All,
I am trying to create a 3-tier application using Apache Tomcat and Toplink:
1. As a part of my servlet startup I create a ServerSession
session = project.createServerSession();
and store it as a static variable. Upon connect I can see that TopLink creates multiple connections. (I assume they are to be pooled between client sessions)
2. All subsequent DB operations are performed using client sessions acquired from that server session:
session.acquireClientSession()
I am running into the following problem:
After very mosdest usage (1 user) I manage to freeze the application as follows:
[TopLink Finer]: 2007.08.19 11:31:44.093--ServerSession(2285943)--Thread(Thread[http-8080-Processor25,5,main])--client acquired
[TopLink Finest]: 2007.08.19 11:31:44.109--ClientSession(15960898)--Thread(Thread[http-8080-Processor25,5,main])--Execute query ReadAllQuery(com.ligolab.application.domain.reporting.PatientResultReport)
[TopLink Fine]: 2007.08.19 11:31:44.109--ServerSession(2285943)--Connection(21849501)--Thread(Thread[http-8080-Processor25,5,main])-- MY SELECT QUERY HERE
[TopLink Finer]: 2007.08.19 11:31:44.921--ClientSession(15960898)--Thread(Thread[http-8080-Processor25,5,main])--client released
---------------------------------------------- [I hit Refresh on my browser here] ---------------
[TopLink Finer]: 2007.08.19 11:31:46.125--ServerSession(2285943)--Thread(Thread[http-8080-Processor24,5,main])--client acquired
[TopLink Finest]: 2007.08.19 11:31:46.125--ClientSession(28210421)--Thread(Thread[http-8080-Processor24,5,main])--Execute query ReadAllQuery(com.ligolab.application.domain.reporting.PatientResultReport)
[TopLink Fine]: 2007.08.19 11:31:46.125--ServerSession(2285943)--Connection(21849501)--Thread(Thread[http-8080-Processor24,5,main])-- MY SELECT QUERY HERE
[TopLink Finer]: 2007.08.19 11:31:47.265--ClientSession(28210421)--Thread(Thread[http-8080-Processor24,5,main])--client released
---------------------------------------------- [I hit Refresh on my browser here] ---------------
[TopLink Finer]: 2007.08.19 11:31:49.062--ServerSession(2285943)--Thread(Thread[http-8080-Processor25,5,main])--client acquired
[TopLink Finest]: 2007.08.19 11:31:49.062--ClientSession(25506524)--Thread(Thread[http-8080-Processor25,5,main])--Execute query ReadAllQuery(com.ligolab.application.domain.reporting.PatientResultReport)
[TopLink Fine]: 2007.08.19 11:31:49.062--ServerSession(2285943)--Connection(21849501)--Thread(Thread[http-8080-Processor25,5,main])-- MY SELECT QUERY HERE
[TopLink Finer]: 2007.08.19 11:31:50.000--ClientSession(25506524)--Thread(Thread[http-8080-Processor25,5,main])--client released
---------------------------------------------- [I hit Refresh on my browser here] ---------------
[TopLink Finer]: 2007.08.19 11:31:56.890--ServerSession(2285943)--Thread(Thread[http-8080-Processor24,5,main])--client acquired
[TopLink Finest]: 2007.08.19 11:31:56.890--ClientSession(19507034)--Thread(Thread[http-8080-Processor24,5,main])--Execute query ReadAllQuery(com.ligolab.application.domain.reporting.PatientResultReport)
After last refresh my Query does not get executed and the application just hangs. If I PAUSE it in debug mode I observe that it is stuck waiting in the ConnectionPool.acquireConnection()
I would appreciate any suggestions!
Tony.

Answer 1

Tony,
TopLink does have its own internal connection pooling by default with a Server Session. This can be changed to use the data sources of the container you are running if available and wanted.
Each read query acquires a connection and releases it once the query is completed. One exception to this is when cursored streams or scrollable cursors are used. These require the connection to be held out of the pool until the application closes the cursor/stream. Do your queries make use of this?
Doug