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I'm seeing random TNS connection closed errors when connecting to one of our databases. It's not affecting all users. (Appears to be happening during spikes of user activity) Occasionally I'm also seeing ORA-12518: TNS:listener could not hand off client connection.

The connections are being made from .Net using the ODP driver. (Which generates a lot of connect/disconnect activity)

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up vote 2 down vote accepted

From here:

Your server is probably running out of memory and need to swap memory to disk.

One cause can be an Oracle process consuming too much memory. A possible workaround is to set following parameter in the listener.ora and restart the listener:


Should you be working with Multi threaded server connections, you might need to increase the value of large_pool_size.

You could examine the listener log file. By issuing the lsrnctl status command you can see log file. Check listener parameter file and see listener version.

See this blog post for other possible causes and additional help: ORA-12518: TNS:listener could not hand off client connection

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Something crazy, but I used to see this issue when I was trying to do an OCI call to a 10g database using an older 9i driver. You might want to check your driver version to make sure it matches the database you're trying to connect to.

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Did it happen all the time with a mismatched driver? Or just randomly? What I'm seeing is random. – jeffspost Jun 16 '09 at 20:32
Totally random - took me 6 months to isolate it, we thought it was a problem with a router for a long time. – Keith Jun 16 '09 at 20:34
I just checked and I'm running the 11g driver, so I doubt that's my problem, but thanks for the idea. I'd upvote it, but I don't have enough reputation yet. :-( – jeffspost Jun 17 '09 at 0:55

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