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From Rob Davies <>
Subject Re: Advice for Scheduler refactor.
Date Thu, 07 May 2015 20:57:53 GMT
Nice! I like what you've done. I originally used ConcurrenthashMap - but found it a bit of
a hog, would be interested if you find different?

> On 7 May 2015, at 19:58, Kevin Burton <> wrote:
>> On Thu, May 7, 2015 at 6:30 AM, Tim Bain <> wrote:
>> I agree with your approach with the WeakRunnable; I think that will achieve
>> the goal without the performance hit of calling purge() after each
>> cancellation.
> I went ahead with this solution and it seems to be working well in
> production.
> Since the unit tests take 24 hours to run , and I haven’t actually been
> able to get them to run, I gave up on that approach and I’m just being very
> careful with my code and making sure we can revert our queue quickly.
> So far my changes have been in production for a week and have been rock
> solid.
> These changes have dramatically improved the performance of ActiveMQ in
> production for us.  The current version of ActiveMQ, without our patches,
> simply can’t scale to this number of queues.
> So far , with my changes, it’s been rock solid, doesn’t suffer the GC
> lockup and GCs are not VERY fast.  They take 30-90 seconds now. Before they
> were locking up ActiveMQ for 20 minutes at a time.  Once I finished with
> the lock bugs then it was that queue GC was taking 100% CPU continually but
> never actually finishing GC.
> Now queue GC is much much faster and everything seems to be solid.
>> If you take on the synchronized keywords, you should consider whether we're
>> worried about concurrent calls to doStart() and doStop().  That scenario
>> could leak a Timer, and the current code doesn't protect against that
>> (you'd need a flag to say whether you've been stopped, and you'd need to
>> check it in doStart() ).
> Agreed. I decided to not take these on because they simply weren’t showing
> up in the profile.  So if it aint broke -don’t fix it.
> The only other issue, really, is the reflection cost of creating a queue.
> But the performance there is linear at least.  The problem with the current
> version of activeMQ is that performance falls exponentially because of
> CopyOnWriteArrayList being used everywhere.  Refactoring those to use
> ConcurrentHashMap seems to completely solve the problem.
> It’s nice when a plan comes together.
> These changes have actually allowed us to ship 5.0 version of our product.
> I have to say that ActiveMQ slowed us to market by about 1-1.5 months… but
> I think I was also asking ActiveMQ to do a lot.  But realistically, it
> should have been able to keep up.  It’s just that internally it was using
> the wrong data structures for our use case.
> -- 
> Founder/CEO
> Location: *San Francisco, CA*
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> <>

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