activemq-users mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Kevin Burton <bur...@spinn3r.com>
Subject Re: Setting expireMessagesPeriod=0 for advisory topics improved GC performance by 2x..
Date Mon, 11 May 2015 19:52:31 GMT
> I hadn't expected purge() to call heapify(), so I was just expecting O(N)
> runtime for the actual removal.  The comments claim the runtime of the
> purge operation is O(N + ClogN) where C is the number of deleted elements
> (which would make it O(N) when C is 1, but looking at the code I think it's
> actually O(N + ((N-C)/2)log((N-C)/2)), which is O(NlogN) when C is 1.  So
> it's not O(N^2), but it's also definitely not O(N) despite the comment's
> claim.
>
>
Yes.  I think this is a more appropriate claim.  But in my experience it
seems to grow larger than NlogN but perhaps there are secondary issues here
like L1/L2 cache hits that dramatically slow it down


> Now I just have it essentially flag the timer task as clear and it will go
> > through the timer queue and not get executed.
> >
>
> Sounds fine, as long as "flag the timer task as clear" also means "call
> TimerTask.cancel(), so that the task's state will be TimerTask.CANCELLED so
> it'll be removed the next time it comes to the top of the queue in
> Timer.mainLoop(), in addition to any WeakReference stuff we may do".  If
> not, you're going to have a lot of no-op TimerTasks that stick around
> forever, so 1) your value of N will grow over time, so even O(N) operations
> will take longer over time, 2) there's still an expensive thread context
> switch even if the task is a nominal no-op, and 3) eventually you could OOM
> due to the memory those no-op TimerTasks take.  Does that match what you've
> implemented?
>
>
Yes.  here’s the new cancel method:

https://gist.github.com/burtonator/6fe3ee640f5f1b27caa2

I call task .cancel() then .clear() (which clears the reference).

and here’s the new SchedulerTimerTask

https://gist.github.com/burtonator/be4bd7b39c250b2b1a0c


-- 

Founder/CEO Spinn3r.com
Location: *San Francisco, CA*
blog: http://burtonator.wordpress.com
… or check out my Google+ profile
<https://plus.google.com/102718274791889610666/posts>

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message