Oracle orphan sessions after server to Windows 2003R2

We have 8.1.7.4 databases running on Windows 2003R2 SP2 Standard Edition.
We previously had these same databases running on Windows 2000 SP4 but have now moved to new servers.

Our clients are a mix of Forms 4.5 (on XP SP2 + Citrix), VB6 using Oracle 8.1.7.4 / Win XP SP2, ODBC via 9.2.0.1 client and .Net clients via 9.2.0.1 client (last 2 being on same Windows 2003R2 SP2 servers).

We are now experiencing a problem where we have orphaned Oracle sessions (ie threads) on the server with no corresponding process on the clients.

This is occurring even when the client shuts the program down cleanly. The SPID is present in v$process for the orphaned sessions. v$session.process lists the client process ID, but that process does not exist on the client PC.

This did not happen when the server was Windows 2000 - nothing else has changed, we are on the exact same patch version on the server and clients.
We can't reproduce on demand - we did make occur for 1 session out of thousands of Forms sessions started via a program. It is not happening for our client programs that use a 9.2.0.5 client.

The problem is that this causes the memory allocated to the oracle.exe process to increase until we reach the 2 GB limit (for Windows standard 32 bit), as occurred the first time we found this problem, and then no new connections are accepted. This actually occurred when oracle.exe was reported as using 1.46 GB of virtual memory (eg by pslist) - see Metalink 46001.1 for explanation of this.

DCD is designed to detect and delete these (you can refer Metalink notes 165659.1 / 151972.1), but we have had serious problems with this previously so I'm loath to turn it on without significant testing.

For now, I've created a script to identify orphaned sessions (based on login age and session inactivity - don't mind that it will detect non-orphans that haven't been used for a long time) and creating the orakill commands to delete these sessions.

Has anyone else experienced these orphan sessions? I'm open to ideas for determining the root cause - note that an upgrade of Oracle clients & server is intended to happen next year.

Thanks,
Bruce Reardon
mailto:bruce.reardon_at_riotinto.com

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