ilooner opened a new pull request #1409: DRILL-6644: Don't reserve space for 
incoming probe batches unnecessarily during the build phase.
URL: https://github.com/apache/drill/pull/1409
 
 
   ## Problem
   
   Previously the memory calculator for HashJoin was reserving space for the 
worst case sized incoming probe batch. This is actually completely unnecessary 
since we won't read probe side data before the build phase anymore after 
DRILL-6453, so this effectively causes memory to be underutilized.
   
   ## Solution
   
   There are two cases we have to handle:
   
   - We received probe side data when fetching the schema. In this case we only 
have to account for the memory consumed by the probe data we received in the 
build phase. Not the worst case incoming probe batch size.
   - We received NO probe side data when fetching the schema for the probe 
side. In this case we don't have to reserve any memory for probe data during 
the build phase.
   
   ## Prerequisite
   
   The PR for DRILL-6453 must be merged first before this can go in. In this PR 
only look at the changes in the last commit.
   
   https://github.com/apache/drill/pull/1408
   

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