[GitHub] [druid] gianm edited a comment on issue #9689: groupBy query: limit push down to segment scan is poor performance

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

gianm edited a comment on issue #9689: groupBy query: limit push down to segment scan is poor performance
URL: https://github.com/apache/druid/issues/9689#issuecomment-613691056
 
 
   >  from a quick look, it looks like we should just delete ByteBufferHashTable and replace all usage by MemoryOpenHashTable which is a clear winner. Do you see any reason for keeping ByteBufferHashTable around anywhere ?
   
   I don't see a reason to keep ByteBufferHashTable around. The only reason I didn't replace all usages of it was time constraints.
   
   Although for the LimitedBufferHashGrouper. specifically, I think in order to migrate that to MemoryOpenHashTable, we'd need to also add a MemoryMinMaxHeap (replacing ByteBufferMinMaxOffsetHeap).
   
   I would suggest refactoring the code of LimitedBufferHashGrouper a bit so rather than subclassing the hashtable and overriding stuff, it instead has a (not-subclasses) MemoryOpenHashTable and a MemoryMinMaxHeap and uses them both together to achieve its ends.

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