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From Shawn Heisey <>
Subject [DBCP] Connection pool not behaving as I expect
Date Thu, 01 Mar 2018 22:33:37 GMT
We have been having some problems lately where our MySQL server hits the
max connection limit (600) and then everything breaks.  When I look into
the problem, I find that our application servers have each made nearly a
hundred connections to the DB and haven't closed any of them for hours.

I'm also using connection pooling in my programs, with the latest DBCP
version.  Those servers don't open nearly as many connections, and have
idle eviction to keep the connection count down.  But when the limit is
reached, these programs suddenly stop working too.

Investigating these problems, I manage to get connected and kill off the
surplus of idle connections, and everything starts working.

Today, a couple of days after the last incident, I realized that we
should *NOT* be having these problems -- because we're using connection
pooling.  The application has open and idle connections to the DB server
... so why is trying to open MORE connections (and obviously failing)
instead of using one of the perfectly good connections that's already
sitting there, unused?

I'm writing here specifically for DBCP on my programs, so I know you
guys probably can't help with Tomcat's connection pooling ... but for
either case my question stands:  Why isn't connection pooling doing its job?


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