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From Tim Bain <tb...@alumni.duke.edu>
Subject Re: I can finally somewhat duplicate the bad bug I’m seeing with ActiveMQ not dispatching messages.
Date Fri, 24 Apr 2015 21:27:44 GMT
If every message has at least one consumer for which the consumer's
selector matches the message, you'll eventually process every message.
Consumers that have no messages matching their selector in the cursor will
be delayed until the messages in front of their next one get consumed, but
they'll do it eventually; I don't think you'd have a complete failure to
process messages as Kevin described.  (Or maybe I'm reading the wrong thing
into Kevin's description.  Kevin, can you confirm that you're getting NO
messages to ANY consumer on your queue?)

Kevin, your screenshots didn't come through in my email client (Gmail) nor
on the Nabble page; can you resend so we can see what you're seeing in JMX?

Also, given the way cursors work, implementing priority using selectors is
never going to work.  At best you'll only be able to prioritize among the
first N messages in the store at any point in time (with N = the number of
messages that will fit into the cursor), which will eventually result in
you having only N lowest-priority messages so you'll process the
low-priority messages while your high-priority consumers sit unable to
reach the high-priority messages deeper in the store.  If you want to use
selectors to implement priority, you're going to have to implement the
enhancements to cursors that Jon and I were talking about on Wednesday.

Tim

On Fri, Apr 24, 2015 at 3:03 PM, Timothy Bish <tabish121@gmail.com> wrote:

> On 04/24/2015 04:50 PM, Kevin Burton wrote:
> > I’ve been working 15 hour days for the last 2-3 weeks trying to resolve
> > this so if this is somewhat incoherent it’s probably due to lack of sleep
> > :-P
> >
> > I think we’re experiencing a bug in ActiveMQ which is VERY hard to
> > reproduce but happens regularly in our production setup.
> >
> > I can’t reproduce it in my test setup because it seems to require real
> > world data.  Every time I try to do so everything works fine.
> >
> > It seems you have to have the following:
> >
> > - a large number of queues which need servicing ( > 1000)
> > - a fairly large number of connections (>2000)
> > - message selectors
> > - a queue that has a large number of messages (5000).
> >
> > I have my test code now reproducing it…
> >
> > Everything works FINE if we have just a few message.  The problems arise
> > once the queue size grows at which point selectors don’t work.
> >
> > It seems like *early* connections win.  If I create a connection to
> > ActiveMQ early, and keep it open, it will work. But new connections don’t
> > work..  Eventually, the existing connections will fail too.
> >
> > Basically, it works JUST FINE without message selectors.
> >
> > I KNOW it’s not my code because I’ve written a basic /simple consumer
> which
> > is literally just raw JMS and is < 50 lines of code.
> >
> > I also know my messages selectors should match.  First.  they do match
> some
> > percentage of the time. Second, when I consume without the message
> > selectors, it works.  I have it print the message headers and I can
> confirm
> > that they should match.
> >
> > This also seems to get worse over time.  The larger the queue, the less
> > chance messages will be serviced, eventually it will just lock up
> entirely.
> >
> >
> > There are no obvious errors in the ActiveMQ log.  Just regarding queue
> GC.
> >
> > The box still has about 40% memory free.  So I don’t think it has any
> issue
> > with memory.  No OutOfMemoryErrors being logged.
> >
> > I think another way to debug this could be to restart activemq itself
> with
> > message tracing. Then try to get the queue to this state again, and try
> to
> > consume messages nd see what’s being logged while it’s failing.
> >
> > What’s frustrating here is that this is the 3rd ActiveMQ workaround I’ve
> > had to implement.
> >
> > the first was because LevelDB was very slow… (artificially slow it
> seems),
> > so then I decided to just use the memory store.  But the memory store
> > doesn’t support priority, so instead, I implemented priority through JMS
> > selectors.  But now JMS selectors don’t work.
> >
> > :-/
> >
> This sounds a lot like the standard issue of having a deep queue and the
> message selector not being able to match because the maxPageSize value
> is limiting what the message cursor will page in.  Have you tried upping
> the maxPageSize option?  See:
> https://issues.apache.org/jira/browse/AMQ-2217
>
> --
> Tim Bish
> Sr Software Engineer | RedHat Inc.
> tim.bish@redhat.com | www.redhat.com
> twitter: @tabish121
> blog: http://timbish.blogspot.com/
>
>

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