I have a real puzzle with "freezing" that I've been struggling with for over a year now. This has been perhaps the best
java forum that I've been a part of, so I'm hoping that you can help. First, I'll describe the layout (see attached flowchart), then the problem.
The Layout
JSP pages and
Server B both make calls to a mysql database through some intermediaries. All calls to the database are brokered by the
Database Server. To get Object O from the database, the
Server B would make the following rmi call: databaseServer.getObjectO(); A JSP page makes a similar rmi call, but through an additional interface class,
JSP Interface Class, which in turn relays the call to
Database Server. For example:
JSP page calls jspInterfaceClass.getObjectO(); causing the instance of
JSP Interface Class to return the results of the call databaseServer.getObjectO();
The Problem
Occasionally, an update call from
Server B randomly hangs as it waits for the update method to return. It is always the same updateMyObjects(Object[] myObjects) method that hangs. The update method doesn't always hang. It succeeds a few thousand times for every hang.
Debug Info
Here are the possibly suspects that I've considered:
bad/invalid data/calls - rerunning the
Server B's process in a way that produces identical results does not result in a hang.
mysql deadlocks - I didn't find any mysql deadlocks despite checking the processlist during a hang.
rmic failures - This doesn't seem likely since I'd naively thing that they should happen for all rmi calls equally.
database server crashes - The first line of the updateMyObjects prints out to a log file. I've verified that this line does not print during a hang.
restarting the database server - I put the call to the update method in a try block and put a long pause, reconnect, and recall the same update method in the catch block. Upon getting a hang, if I restart the
Database Server the method runs without trouble.
synchronization - I've tried making every method in the
Database Server that communicates with relevant mysql table be synchronized. This didn't help the problem at all. Al methods in the
JSP Interface Class are synchronized.
Any ideas?
![[Thumbnail for flowchart.jpg]](/t/546747/a/2450/flowchart.jpg "Filename: flowchart.jpg
Description: Flow chart")
