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From Tim Bain <tb...@alumni.duke.edu>
Subject Re: high GC activity yields a high percentage of dead letter queue messages.
Date Tue, 30 Dec 2014 21:42:03 GMT
That sounds like a plausible explanation of why you DLQ filled in that
situation.  The more interesting question is what caused the GCing behavior.

I assume you don't have any GC logs/memory dumps to do forensics against,
so you're stuck trying to reproduce the problem so you can have something
to analyze?  If so, remember that you don't have to actually get to the
point of doing continual GCs (which might take weeks); it's enough to see
that the amount of Old Gen usage observed immediately after you force a
full GC (e.g. from the Memory tab of JConsole) increases between successive
full GCs over a non-trivial time period.  Then just analyze what's causing
the increase and that should be your answer.
On Dec 30, 2014 2:06 PM, "Kevin Burton" <burton@spinn3r.com> wrote:

> I think I figured out a realistic theory as to why my broker died last week
> and ended up with my entire queue moving to the dead letter queue.
>
> The problem happens when ActiveMQ goes into a full-GC loop where it
> continually spends 100% CPU doing full -GCs.
>
> messages are still served, but only say 1% of them (because there’s no CPU
> left to do much work).
>
> The problem comes from sessions or client acks where you have to commit()
> or ack a message manually.
>
> This never happens.  Because the broker is spending all time doing GCs.
>
> So the 1% of messages that leave, only have a 1% chance of being ack’d…
> which means that 99% of messages that are served by the broker aren’t
> ack’d.
>
> This keeps happening slowly and your entire queue will be drained with
> messages going into the DLQ.
>
> It would probably end up with around say a small percentage of your
> messages being processed.  But the majority would end up in the DLQ.
>
>
>
> --
>
> 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>
> <http://spinn3r.com>
>

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