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https://issues.apache.org/jira/browse/NIFI-4589?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16261463#comment-16261463
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ASF GitHub Bot commented on NIFI-4589:
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Github user mosermw commented on the issue:
https://github.com/apache/nifi/pull/2260
Code looks good, full build with contrib-check passes, and I tested a small
flow with success & failure results as expected. +1 merged.
There is a comment in the ProtocolHandshake class that I would modify to
reflect version 3 of DistributedMapCache, but it's just a comment and I can
take care of that in my upcoming PR.
> Allow multiple keys in FetchDistributedMapCache
> -----------------------------------------------
>
> Key: NIFI-4589
> URL: https://issues.apache.org/jira/browse/NIFI-4589
> Project: Apache NiFi
> Issue Type: Improvement
> Components: Extensions
> Reporter: Matt Burgess
> Assignee: Matt Burgess
>
> Currently (1.4.0) FetchDistributedMapCache will look up a single key and
> place the value (if present) in either the flow file content or a user-named
> attribute, depending on the value of the "Put Cache Value In Attribute"
> property. If the user wishes to look up more than one value, they need
> multiple FetchDistributedMapCache processors, and each would make one call to
> the server to get a single key.
> A useful improvement would be to allow multiple keys to be retrieved at once
> by FetchDistributedMapCache. This would likely involve the following:
> 1) Update documentation and code to accept a comma-separated list of Cache
> Key Identifiers
> 2) If a single Cache Key Identifier is specified, current behavior is
> retained (i.e. output to flow file content or a specified attribute)
> 3) If multiple Cache Key Identifiers are specified, then Put Cache Value In
> Attribute must be set, and the attributes will be prefixed by the value of
> said property, followed by a period, followed by the evaluated cache key. So
> if Cache Key Identifier is set to "field1, field2" and Put Cache Value In
> Attribute is set to "myattrs", then the value for field1 will be placed in
> the "myattrs.field1" attribute, and field2's value in "myattrs.field2"
> respectively.
> 4) Due to the possible presence of Expression Language in the Cache Key
> Identifier property, it may not be possible to determine whether multiple
> cache keys are present (i.e. a single EL function that generates a
> comma-separated list), so the requirement on Put Cache Value In Attribute
> being set must be checked at validation time (if possible) and also run-time
> 5) To make this fetch efficient, a method "subMap" can be created on the
> DistributedMapCache API, so multiple keys can be passed and multiple
> key/value pairs can be returned in a single call to the cache server.
> 6) #5 implies a new protocol version (would be 3 at the time of this writing)
> be added to the DistributedMapCache API
> 7) If protocol negotiation results in a lower version being used, then the
> client should gracefully degrade into using the "subMap" operation to make
> multiple calls to the "get" operation, and fill in the result map manually.
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