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In this article, I will discuss one of the most exciting new features coming with NiFi 1.7.0 is the possibility of terminating running threads from the NiFi UI.

I can think of a couple of examples in the previous NiFi versions where we either had to wait for a running thread to end before being able to make any changes to the processor configs or, in worst case scenarios, restart the NiFi cluster because of some thread is in a deadlock condition. For example

  • An ExecuteSQL processor is stuck since the source RDBMS is not able to handle the data pull and has yielded under pressure. Or the other processes are not able to use the RDBMS since resources are hogged by this complete database scan operation. Either we wait for a literally infinite period of time or if the problem is serious, stop the cluster all together.
  • Some custom script/processor has a deadlock situation and the thread won't stop ever. The only option we have in this scenario was to restart the machine/cluster running that process.

Thanks to NiFi 1.7.0, now we have a more elegant solution to these kinds of problems, Terminate the thread from the UI itself.

Follows a quick example of how we can do it.

So for my flow, I created a sample flow with a GenerateFlowFile processor which is running continuously on all the possible nodes, a single one, in this case, my Mac 🙂

I have made the thread to run for longer once initiated and hence, even if I stop the processor, the thread will still keep on running. Have a look into the snapshots below.

77902-screen-shot-2018-07-02-at-15003-pm.png

77903-screen-shot-2018-07-02-at-15551-pm.png

When I stopped the processor, the number of thread increase from 1 to 2, since now the thread to stop the processor is waiting for actively running thread. But with this new version of NiFi, NiFi 1.7.0, we have this option of terminating the threads explicitly from the UI itself, see snapshot #2 for the Terminate option.

When the Terminate option is chosen

  • Interrupt for the thread will be issued.
  • A new instance of the processor will be created.
  • The old instance will be eventually shut down.

So here we are! With the new power to interrupt the threads from the NiFi UI. But please be careful! With greater powers, come greater responsibilities! I will add more information on what can be the probable issues, if any, of stopping the threads in between.

Please feel free to leave comments to let know about the flow and for questions and queries.

Hope that helps!

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‎08-17-2019 07:02 AM
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