[GitHub] [incubator-druid] leventov edited a comment on issue #7571: Optimize coordinator API to retrieve segments with overshadowed status

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leventov edited a comment on issue #7571: Optimize coordinator API to retrieve segments with overshadowed status
URL: https://github.com/apache/incubator-druid/issues/7571#issuecomment-496264473
 
 
   Regarding interning - we have to get rid of them anyway: #7395 explains how. If a segment first appears in `BrokerServerView`, it can be created as `SegmentWithOvershadowedStatus(isOvershadowed=false)`. Then if it later appears in `MetadataSegmentView` and it is not actually overshadowed, we reuse the existing object by probing `BrokerServerView`. If the arrived object has `isOvershadowed=true`, we just lose the opportunity to deduplicate this segment, but we expect it for the minority of segments, so that's fine.
   
   Regarding `SegmentWithOvershadowedStatus(isOvershadowed=false)` objects in `BrokerServerView` while the actual status is unknown: it seems weird at first glance but it's actually fine. The rule is that to probe `isOvershadowed` status we should *always* go through `MetadataSegmentView`. To guard against misuse, we can prohibit casting to `SegmentWithOvershadowedStatus` in the codebase on the Checkstyle or IntelliJ level.
   
   > What do you mean by 'prohibit' @leventov? I followed the link, and I don't see a suggestion about prohibiting equals and hashCode. (Just about prohibiting using DataSegments as keys in a map, which seems reasonable, given that usually people probably meant to use SegmentId.)
   
   Sorry, I didn't re-check what did I propose there. No, I don't suggest to prohibit.  I suggest exactly what is written in https://github.com/apache/incubator-druid/issues/6358#issuecomment-489102183.

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