[Deploying Sakai] possible dbcp issue
Charles Hedrick
hedrick at rutgers.edu
Wed Sep 9 15:31:33 PDT 2009
We're seeing an odd kind of loss of database connections in 2.6. This
is mysql 4.1, Java 6, and the dbcp/pool shipped with 2.6 (1.2.2 and
1.3).
We disable all dynamic adjustment and ask for 300 connections. After a
few days we have 275 idle and 25 in use. "netstat -n -a | grep 3306"
shows only 275 connections. Of course 275 is still plenty, but I worry
about the trend.
It looks to me like those 25 "in use" actually are lost in some odd
way. I don't see how Sakai could be doing it, as Sakai would just
return connections to the pool, not close them. Maybe mysql is someone
closing the connections, but (1) I can't see why it would; it didn't
with 2.5 (2) you'd think Sakai would still return the connection, and
it wouid no longer show as in use.
I can't help suspecting a possible issue with dbcp/pool.
I'd appreciate if if you'd try the attached jsp and see if the total
of active and idle matches the number of connections shown by netstat.
I'm thinking of running a job nightly that checks the number of
connections with netstat, and creates additional connections in the
pool as needed. Doing so requires some magic, but not much. (The
problem is that you need to get to the underlying GenericObjectPool,
which is a protected field of the BasicDataSource. It turns out that
using introspection, you can access protected fields.)
I'm coming close to writing my own pool code. We tried c3po a couple
of years ago and it was no better. If you implement a single, simple
strategy, it's easy enough to do.
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