How to auto reconnect Oracle connection pool after connection interruption

You've done good research. I'd say, go ahead with BoneCP. Some years ago I would have suggested c3p0, but it has currently some open and unresolved issues as well. Too bad, actually. The BoneCP author is by the way also active here at SO.

There is no 100% right answer to this. It is a matter of trade-off and context.

• Most of the times, testOnBorrow is the least risky since it ensures (as best it can) that before a connection is returned from the pool for your use, a basic sanity check has been made that the client and db-server are on talking terms.
• It still doesn't prevent the race condition of the server connection going down, between the time 'the sanity check' was made & the time your application used the connection.

• But considering this as a corner-case, the testOnBorrow gives pretty good assurance.

• Now the trade-off with that is that, every time you request a connection, a query (no matter how light-weight) is made to the database-server. This maybe very fast, but the cost is still not zero.

And if you have a busy application, with very good database-connection-reliability, then you'll start seeing from the data, that the COST of "validity check on every connection-request from the pool" outweighs the benefits of detecting connection issues.

• On the other hand, if your application is not uniformly busy (like most real-world applications) then it is extremely beneficial to have the testOnBorrow option.

• It ensures to the max, that you have a good connection before you use it. Especially considering the cost (retry + manual intervention + loss of workflow etc.) of "not being able to recover easily" from a failed DB operation.

• Now imagine if you have the testOnIdle option. This requires that your connections go idle (dependent on the idle timeout of the connection) before a sanity check can be made.

• This is a performance improvement over testOnBorrow but it comes with its own disadvantages.
  • Real world app-to-db-connections are not just idle-timeout-based breakage, they can be dropped based on firewall rules, n/w congestion, db-server-undergoing maintenance/patching etc.
  • So it goes back to the data-measurement of how many connection errors were observed in the data, when you did not have any sort of "connection validation".
• And one thing to watch out with this option is when you have your pool working the best with max connections and your app performing well, and for some reason if your db-server undergoes a restart or likewise. All the live connections (from a client perspective) will now mostly error out, till the idle timeout kicks-off. So your db-issue (which would have been a fire-fight) is now compounded a bit, till the app connections get well again or you restart the app as well.

And one last data point is that for some applications, the critical-path is not the "validation query" time (in lower millis hopefully). The applications have bigger issues to deal with. And of course, for some applications, that time is very significant.