Obviously fixing the app is the best choice, but I have a feeling that this is going to recur again and again since the app is poorly maintained but still under active development (code base too large for the developer assigned to it). The developer is likely to accidentally cause connection leaks in the future.
This problem is also very easy to cause because doing this:
c = sqlconnect("database")
c = sqlconnect("database")Causes TWO connections to be made, and the first connection made is now (as far as I can see) impossible to close without closing the application. The language (Visual Foxpro) does not garbage collect connections and so any connection whose handle is lost still takes up one of the slots.
On the server side, I can detect this condition using ps -A or lsof; but I have not thought of a good solution to use when this is noticed. One possibility is to just shut down the database and restart it when this happens. I did some research into finding out if it was possible to break a specific TCP connection (this is linux 2.6 kernel--platform specific tools/commands ok). For example, could I use hping to break the connections?
Does anyone know a safe way to shutdown just one backend (if it is idle)?
Another possibility that I can think of is per ip address connection limits. How hard would that be?
Paul Tillotson
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