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
##########
File path:
server/src/main/java/org/apache/druid/segment/realtime/appenderator/AppenderatorImpl.java
##########
@@ -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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