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https://issues.apache.org/jira/browse/NIFI-190?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14701350#comment-14701350
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Aldrin Piri commented on NIFI-190:
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I like the features that the DistributedMapCacheClient provides but also wonder
what happens when people use this for the case of files showing up on a
particular system. If part of the resultant processor can be something that
dictates node vs cluster for the map and provides appropriate key management we
can open up flexibility for a variety of use cases people may have.
I could see cases where we release everything as in the original case proposed
in the description, but also cases where each individual instance of the
HoldFile needs its own signal in a clustered environment.
> HoldFile processor
> ------------------
>
> Key: NIFI-190
> URL: https://issues.apache.org/jira/browse/NIFI-190
> Project: Apache NiFi
> Issue Type: New Feature
> Components: Extensions
> Reporter: Joseph Gresock
> Assignee: Bryan Bende
> Priority: Minor
> Attachments: HoldFile_example.xml
>
>
> Our team has developed a processor for the following use case:
> * Format A needs to be sent to Endpoint A
> * Format B needs to be sent to Endpoint B, but should not proceed until A has
> reached Endpoint A. We most commonly have this restriction when Endpoint B
> requires some output of Endpoint A.
> The proposed HoldFile processor takes 2 types of flow files as input:
> * Files to be held
> * Signal files that can release corresponding held files, based on the value
> of a configurable "release" attribute
> Signal files are distinguished from held files by the presence of the
> "flow.file.release.value" attribute. The processor is configured with a
> "Release Signal Attribute". Held files with this attribute whose value
> matches a received signal value will be released.
> An example:
> HoldFile is configured with Release Signal Attribute = "myId". Its 'Hold'
> relationship routes back onto itself.
> 1. flowFile 1 { myId : "123" } enters HoldFile. It is routed to the 'Hold'
> relationship
> 2. flowFile 2 { flow.file.release.value : "123" } enters HoldFile. flowfile
> 1 is then routed to 'Release', and flow file 2 is removed from the session.
> Signal flow files will also copy their attributes to matching held files,
> unless otherwise indicated. This is what allows the output of Endpoint A to
> pass to Endpoint B, above.
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