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https://issues.apache.org/jira/browse/NIFI-4994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16414154#comment-16414154
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ASF GitHub Bot commented on NIFI-4994:
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Github user bbende commented on the issue:
https://github.com/apache/nifi/pull/2568
This may need to be updated based on the recent changes in master that were
just made today, basically the reloadIfNecessary method is going to return
immediately if the component has a null fingerprint, so it would never hit the
new logic in this PR.
> Reload instance class loader at every component restart
> -------------------------------------------------------
>
> Key: NIFI-4994
> URL: https://issues.apache.org/jira/browse/NIFI-4994
> Project: Apache NiFi
> Issue Type: Improvement
> Components: Core Framework
> Reporter: Koji Kawamura
> Assignee: Koji Kawamura
> Priority: Major
>
> h2. Current Class loader reload mechanism
> NiFi framework provides RequiresInstanceClassLoading to annotate components
> (Processor, Controller Service or Reporting Task) to use per instance class
> loader. Instance class loaders are reloaded when associated components are
> restarted, if any component property flagged as
> 'dynamicallyModifiesClasspath' is updated. Such component property is used to
> let user specify additional class pass resource URLs. E.g. PutHDFS
> 'Additional Classpath Resources'.
> h2. Limitation of current mechanism
> Current mechanism requires component properties to trigger reloading to
> represent class path resource URLs. That works well in scenarios for users to
> add/del/mod additional class path resources.
> However there is different needs for reloading instance class loader. That is
> re-initializing static state in dependencies.
> For example, ReportLineageToAtlas reporting task uses Atlas client library,
> and the library has static code blocks to initialize its dependencies, such
> as Kafka client with parameters passed by NiFi reporting task based on user
> inputs. Once the initialization is done, there is no way to re-initialize
> those objects, meaning even if NiFi user changes reporting task
> configuration, those will not be able to reflected.
> https://github.com/apache/atlas/blob/master/notification/src/main/java/org/apache/atlas/hook/AtlasHook.java#L63
> The only possible operations to reset such static state are, creating another
> instance, configure the instance again, remove the old one and start new one.
> Or restart NiFi process. This limitation affects UX negatively.
> h2. Improvement design
> Possible approaches are:
> # Enhance RequiresInstanceClassLoading annotation so that custom components
> can specify whether it needs to be reloaded on every component restart
> without condition.
> # Add new PropertyDescriptor instance field to denote that instance class
> loader needs to be reloaded if a property is changed. Similar to
> 'dynamicallyModifiesClasspath' but for configurations other than URI. Then,
> include those property value to
> AbstractConfiguredComponent.additionalResourcesFingerprint
> No.1 is more naive approach, but require less framework code change. No.2
> looks redundant, also could be error-prone, e.g. by forgetting to mark some
> properties.
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