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From Mark Hellkamp <mark.hellk...@theplatform.com>
Subject Concurrent access problems?
Date Wed, 30 Aug 2006 20:10:02 GMT
We are trying to use Derby embedded in our web application but are running into
some serious resource problems when processing concurrent requests. When we are
performing load testing on the application we are experiencing serious
slowdowns, even when running only a few concurrent threads. We are noticing that
the process handle count on our application keeps growing during our tests,
until the machine becomes completely unresponsive. We have isolated the problem
to Derby and I have moved Derby out of the application process by running it in
Network Server mode. In this configuration we can see that the handle count on
the Derby process will grow as we add more concurrent threads accessing the
application. Looking at the handles for the Derby process, it appears that the
number of Semaphores keeps increasing. I'm not sure if this is normal or this
indicates a problem, but it seems a bit suspicious. 

I also completely swapped out Derby with MySql to verify that the application
was not at fault (we are using Spring + Hibernate for data access). Under MySQl
we did not see a significant performance degradation with multiple threads, and
the handle count remained fairly steady on the database.

Does Derby have problems with concurrent access? Our tests are doing read only
queries against the database so read/write contention should not be a problem. I
am extremely perplexed by this problem. Anyone have any ideas?


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