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https://issues.apache.org/jira/browse/NIFI-1582?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Joseph Percivall reopened NIFI-1582:
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Re-opening as the logic to update the state should use "replaceState" and not
"setState"[1]
[1]
https://github.com/apache/nifi/blob/master/nifi-nar-bundles/nifi-update-attribute-bundle/nifi-update-attribute-processor/src/main/java/org/apache/nifi/processors/attributes/UpdateAttribute.java#L673
> New processor to update attributes with state
> ---------------------------------------------
>
> Key: NIFI-1582
> URL: https://issues.apache.org/jira/browse/NIFI-1582
> Project: Apache NiFi
> Issue Type: New Feature
> Reporter: Joseph Percivall
> Assignee: Joseph Percivall
> Fix For: 1.2.0
>
>
> This idea was sparked by a thread on the user list and should allow basic
> data science:
> I expect that in the future I’ll need something a little more sophisticated
> but for now my problem is very simple:
> I want to be able to trigger an alert (only once) when an attribute in an
> incoming stream, for instance, goes over a predefined threshold. The
> Processor should then trigger (only once again) another trigger when the
> signal goes back to normal (below threshold). Basically a RouteByAttribute
> but with memory.
> Thanks
> Claudio
> ------------------------------------------------
> Hello Claudio,
> Your use-case actually could leverage a couple of recently added features to
> create a really cool open-source processor. The two key features that were
> added are State Management and the ability to reference processor specific
> variables in expression language. You can take a look at RouteText to see
> both in action.
> By utilizing both you can create a processor that is configured with multiple
> Expression language expressions. There would be dynamic properties which
> would accept expression language and then store the evaluated value via state
> management. Then there would be a routing property (that supports expression
> language) that could simply add an attribute to the flowfile with the
> evaluated value which would allow it to be used by flowing processors for
> routing.
> This would allow you to do your use-case where you store the value for the
> incoming stream and route differently once you go over a threshold. It could
> even allow more complex use-cases. One instance, I believe, would be possible
> is to have a running average and standard deviation and route data to
> different locations based on it's standard deviation.
> You can think of this like an UpdateAttribute with the ability to store and
> calculate variables using expression language.
> Joe
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