Running out of DB connections!

Question

I\'m running a Spring/Hibernate connecting to MySQL setup using c3p0 as my connection pool. For some bizarre reason it runs out of connections when the system is under load (of

Answer 1

Try enabling logging and setting the c3p0.debugUnreturnedConnectionStackTraces property to true. Also set c3p0.unreturnedConnectionTimeout to something smaller than your average query time (1 sec?). Then any thing that takes longer than the timeout will log a stack trace. This should allow you to narrow down things pretty quickly.

If there's no pattern to the stack traces, it could just be that your pool is too small. You said 100 concurrent users, but any idea how many queries per second this is? If it's 100 queries per second and you have 20 connections, then each sql execution needs to take less than 200 ms (20 connections => 20 total seconds of work per sec of wall clock time to do 100 queries).