[Deploying Sakai] [Building Sakai] Strange database connection memory issue at U-M
Jason Shao (CampusEAI Consortium)
jason_shao at campuseai.org
Thu Sep 17 12:57:03 PDT 2009
c3p0 seems to have some interesting options:
softResetDefaultUser(), softReset( username, password ) and
For flushing/manipulating pools if you think something is leaking... And
looks like they're exposed as JMX Mbeans...
On 9/17/09 3:24 PM, "Noah Botimer" <botimer at umich.edu> wrote:
> I think we would do well to consider a simple work queue. We would
> push things that are expected to run long there. I'd say start with a
> generous estimate (10 sec at our scale, maybe?). Instrumenting the
> pool to know how long connections are held would help identify
> candidates to be taken out of immediate mode into queued mode. Some
> of these pieces would need asynchronous handling / notification at
> the UI.
> Once there, we could incrementally tune our attention threshold
> closer to the practical limits of instantaneous vs. queued work
> (maybe 2 seconds per thread?). As the set of things we'd break by
> imposing thread timeouts dwindled, we could consider being vicious to
> threads running unexpectedly long. With a reasonable, consistent
> infrastructure for deciding which mode something should use, the
> decision is much less daunting and the rules of "fast, queued, or
> killed" are tolerable.
> In this model, we would gain practical expertise in how to deal with
> failures more gracefully. I believe our current model is too
> optimistic, generally assuming complete success of every operation
> attempted, which adds brittleness to the app and data. It is worth
> studying each of the big cloud solutions here to see patterns and
> The important thing to note is that there is a very gentle ramp
> available here. A little tooling for deferred/notified work and
> tracking ill-behaved transactions wouldn't mandate immediate overhaul
> of all code. It would just give us a way to start moving toward a
> more resilient platform without the all-or-nothing paralysis that is
> easy to find in these topics.
> Please also note that this exercise need not be restricted to 2.x or
> 3.x. There are real scalability needs to consider on either platform
> and the basic techniques and wisdom (if not code) are transferrable.
> On Sep 17, 2009, at 2:53 PM, Speelmon, Lance Day wrote:
>> Perhaps - probably the right place to start looking. The problem is
>> that the tools to help troubleshoot these kind of leaks cannot be used
>> in production environments. For example, if you tell the connection
>> pool to force return connections to the pool after a set amount of
>> time - it interferes with batch activities. So, then the question
>> becomes: can these leaks be triggered in a test environment? Or maybe
>> batch should be running out of a separate pool to allow this kind of
>> troubleshooting? L
>> Lance Speelmon
>> Scholarly Technologist
>> On Sep 17, 2009, at 2:31 PM, Seth Theriault wrote:
>>> Sean DeMonner wrote:
>>>> We've wondered that too, but haven't found anything that is
>>>> running at those times. The jumps are also not consistently
>>>> spaced so we haven't seen a pattern.
>>> I am thinking that there is some new JDBC-related code in 2.6 and
>>> the database connections are not being closed properly (I guess
>>> in this case, it would mean releasing the conns back to the
>>> pool). I know that Michigan has the capacity to have a large sets
>>> of results returned from any query.
>>> Just a thought.
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