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From Joe Witt <>
Subject Re: Queue wasn't emptying
Date Fri, 06 Nov 2015 16:33:43 GMT

Can you share your flow configuration that we could possibly use to
replicate this?  Perhaps turn this into a JIRA and attach that.

Also anytime you see something that appears 'stuck' please try to get
a stack dump (bin/ dump)  As if there is truly a stuck thread
we'll see it there and what it is blocked on.


On Fri, Nov 6, 2015 at 11:25 AM, Elli Schwarz <> wrote:
> I had a queue that built up overnight with several thousand flowfiles. The
> queue was pointing to a RouteOnAttribute processor, which was running. For
> some reason, the RouteOnAttribute processor wasn't emptying the queue so the
> queue just built up. Stopping and starting the processor didn't help.
> However, simply restarting Nifi got the flow moving again. I can't figure
> out why the queue was stuck.
> What could cause a queue to build up like that? How would restarting Nifi
> get it going again? There weren't any errors in the log.  I did have
> backpressure on the relationship to the processor after the RouteOnAttribute
> set to 1, but that queue was empty. There was no backpressure on the queue
> heading in to the RouteOnAttribute processor. The RouteOnAttribute processor
> has a Penalty Duration and a Yield of 1 sec. The relationships all used the
> PriorityAttributeAnalyzer as the prioritizer.
> The interesting thing is I had the exact same problem on two different nifis
> (one was version 0.2.0 and one 0.3.0). The same type of flow files were
> going from one to the other using site-to-site (I was doing this for load
> balancing). On the other Nifi, instead of restarting, I added another
> RouteOnAttribute processor and rerouted the stuck queue to the new one
> instead, and that also got things moving again. (I have a backpressure since
> the processor after the RouteOnAttribute is a ControlRate processor, and I
> only want to allow 1 flowfile through per second so as not to overwhelm the
> system downstream. The backpressure is to assist with load balancing, so if
> one pathway fills up, I have the other pathway which uses the site-to-site
> to route the flow to the other nifi).
> Is there some combination of backpressure, penalty or yield along with
> prioritization that could cause a kind of deadlock-like situation? Any ideas
> as to how I can prevent this from occurring?
> Thanks!
> -Elli

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