I've written before, trying to track down problems with our database
server getting too many connections.
Based on what I can see of how my programs (using dbcp2) are working,
everything seems to be fine there. I've added logging to tell me how
many idle and active connections there are in the pool, and those
numbers stay low.
So now I need to track down what's happening in our webapps, most of
which are Liferay-based, and all of which are running in Tomcat. And
I've learned that they're using the Tomcat implementation of dbcp for
database access. I think it's Tomcat version 7, but I will need to
check to make sure.
I've figured out how to log the number of active and idle connections,
by casting the DataSource to the tomcat dbcp object actually in use.
Once I can get the developers to actually update a production system
with that code, I will be able to see whether (as I suspect) the
"active" count in the pool is staying abnormally high. I'm betting that
there's somewhere in the webapp code that a connection is retrieved from
the pool, used for some work, and never closed.
I have a main question, and then a semi-related but very different question.
Main Question: Does dbcp by chance record a stacktrace of the code that
requests a connection from the pool? I would like to poke my way
through the active connections (entry point being the DataSource
implementation), and ask them where in our code they were requested. I
have to do this in the Tomcat fork of dbcp, and I know I'm not on a
Tomcat mailing list, but I'm hoping that whatever you can tell me will
apply to that version too. If I can get a stacktrace of where each
connection was requested, I can pinpoint problematic code a lot faster.
There is a LOT of code that uses the database, scattered across a lot of
git repositories. If I could grep the code easily to find them all, I
would.
Side question: Why has Tomcat maintained what looks like a fork of dbcp
for such a long time period? If they really believe their
implementation has an advantage, it seems like everyone would benefit if
they worked to get the upstream library to offer the same advantages.
Am I drifting into flamewar territory by even wondering about this? I
did find the tomcat documentation page about their connection pool. It
basically reads to me as "Commons DBCP is substandard and bloated.
These are the many ways that our implementation is better."
https://tomcat.apache.org/tomcat-9.0-doc/jdbc-pool.html
I haven't compared DBCP with other pool implementations, but my work
with DBCP has never run into any problems that weren't my own fault.
This mailing list has shown a high degree of patience with my dumb
questions.
Thanks,
Shawn
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