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https://issues.apache.org/jira/browse/NIFI-7438?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17143980#comment-17143980
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Matt Burgess commented on NIFI-7438:
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I agree and wish that property was required, perhaps we can do so for NiFi 2.0.
When we added the property we didn't make it required because there wasn't a
reliable default value (as each RDBMS has its own dialect of SQL and thus its
own legit query for validating connections without doing real work). Making it
required without a default value would invalidate all existing instances of the
processor, so the decision was made to add the property as optional.
> Controller Service UI hangs since controller service doesn't handle
> reconnections properly
> ------------------------------------------------------------------------------------------
>
> Key: NIFI-7438
> URL: https://issues.apache.org/jira/browse/NIFI-7438
> Project: Apache NiFi
> Issue Type: Bug
> Components: Configuration, Core Framework
> Affects Versions: 1.11.1, 1.11.2, 1.11.3, 1.11.4
> Environment: RHEL 7.6
> NiFi on Docker
> Reporter: Christian Danner
> Priority: Major
> Attachments: image-2020-05-11-13-38-30-457.png,
> nifi-grafana-dashboard-controller-service-stress.png
>
>
> We encounter Problems in showing and managing Controller Services on NiFi
> Servers that run longer than connected systems we use to connect via
> Controller Services. Viewing such Controller Services takes about 1 minute to
> open the view and then shows multiple instances of it (see screenshot).
> e.g. A "DBCPConnectionPool 1.11.4" shows multiple "Supported Controller
> Services" all the "DBCPService 1.11.4 from org.apache.nifi -
> nifi-standard-services-api-nar" (19 occurances) as well as shows multiple
> Groups of "Processors" {color:#172b4d}(19 occurances){color} with the same
> instances (9 processor instances).
>
> In this specific case we have a connection to a database server that is
> shutdown during the night (DEV environment). NiFi Server continues to run
> while database is not reachable.
> We suspect that when the database comes available again, it will load the
> controller service completely while not unloading old sessions. Disabling and
> re-enabling the controller service doesn't solve the issue, only a complete
> NiFI Server restart fixes this issue.
> All related processors also fail to execute defined "ExecuteSQL" Processors
> until we restarted the Controller Services at least. We get a
> "SocketException" since it tries to make an attempt on the old connection
> which is not active anymore. For us it is important to have a "Infinite
> Connection" while interacting with the database ({color:#262626}Max
> Connection Lifetime{color:#003000} = -1).{color}{color}
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