[GitHub] [incubator-druid] himanshug commented on a change in pull request #6699: release mmap immediately after merge indexes

[GitBox <gi...@apache.org>]

himanshug commented on a change in pull request #6699: release mmap immediately after merge indexes
URL: https://github.com/apache/incubator-druid/pull/6699#discussion_r282670263
 
 

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 File path: server/src/main/java/org/apache/druid/segment/realtime/appenderator/AppenderatorImpl.java
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 @@ -716,8 +717,20 @@ private DataSegment mergeAndPush(final SegmentIdentifier identifier, final Sink
           closer.register(segmentAndCloseable.rhs);
         }
 
-        mergedFile = indexMerger.mergeQueryableIndex(
-            indexes,
 
 Review comment:
   so my understanding is that, this is useful in case when, on realtime process, very small subset of columns/data in the intermediate persisted segments is being read from queries.
   some commentary in the code along those lines would be great.
   overall, this patch looks useful to me.
   
   "swap after merge" is further useful to reduce inode count, but the swap would be tricky to implement as there might be queries underway on the indexes just merged.
   
   I think O_DIRECT is whole other beast and would require significant performance regression testing in this case.

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