Out of control query

I have an inventory system based on PostgreSQL 8.3.5, JBoss, Hibernate......

I have a query builder that lets users filter data in a fairly complex way.

For some reason the search gets out of control and consumes all CPU.

I set my statement timeout to 2 minutes and this keeps the system from going down totally, but this is happening much more frequently than it used to.

I can find the problem with the individual query easily enough, but I would like a more general solution.

What seems strange to me is that one one core of my Quad core x5472 is 100%.  The others show minimal usage.

I would think that other users would get a different core and one query could not deadlock the whole system for everyone.

Do you think this is due to my Postgres or JBoss AS configuration for database connections?

Any advice will be greatly appreciated.