I fixed some bug related to the way we were using BasicDataSource and though I understand part of it I still have some questions unanswered :)
Problem: The application was not able to auto-connect to the database after a db failure.
Application is using org.apache.commons.dbcp.BasicDataSource class as a TCP-connection pool for a JDBC connection to Oracle db.
Fix: After some research I discovered that in BasicDataSource testOnBorrow and testOnreturn were not set. I provided the validation query to test connections. This fixed the problem
Max no of connections in pool was set to 1
My Understanding: The connection pool would hand over a connection to the application. What I think was happening was the application MAGICALLY returned the bad collection to the pool when it db crashed . Now since the Pool does not know if it is a bad connection it would hand over the same connection to the application next time it needs it causing the application to not auto-reconnect to db.
Now, after the fix.. whenever a bad connection is returned to the connection pool it would be discarded and wont be used again because of the fix I made above.
Now I know that BasicDataSource wraps the connection before giving to the application, such that whenever application says con.close ..BasicDataSource would know that the connection is not used any more.. it will take care of either returning the connection to the pool or discardigg etc.
Unanswered Question: However what I do not understand is what makes the application MAGICALLY return the connection to the connection pool when its broken[Note that con.close method is not called when the connection exits un-gracefully]. There is no way of BasicDataSource to know that the connection closed or there is ?. Can someone point me to code for that ?
I my overall understanding connect of why the fix worked ??