[GitHub] [incubator-druid] leventov opened a new issue #7391: MetadataSegmentView should correctly handle the situation of Coordinator being down or changed leadership

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leventov opened a new issue #7391: MetadataSegmentView should correctly handle the situation of Coordinator being down or changed leadership
URL: https://github.com/apache/incubator-druid/issues/7391
 
 
   Regardless of whether any of the designs proposed for `MetadataSegmentView` here: https://github.com/apache/incubator-druid/issues/6834#issuecomment-478569365 is applied, `MetadataSegmentView` should document its behavior in the face of the Coordinator being down, or just started, or leadership changed.
   
   Currently, there is a single comment ["Note that coordinator must be up to get segments"](https://github.com/apache/incubator-druid/pull/6901/files#diff-5707cd19ee7a43a258f29e61fd385d4cR181) which, IMO, only adds FUD and doesn't explain anything.
   
   Ideally, `MetadataSegmentView` should correctly recognize the situations of changed Coordinator's leadership and not to flush all cached published segments.
   
   Explanation may look like the following:
   ```
   /**
    * When Coordinator is just started or leadership changed,
    * its SegmentsMetadata is unpopulated. Then the endpoint /metadata/abc/foo/bar
    * which we are querying returns code XXX (see {@link DataSourcesResource#theRelevantMethod}).
    * We process this code here and don't flush {@link #cachedPublishedSegments} in this case.
    */
   ```
   
   @FYI @surekhasaharan 

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