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Subject [GitHub] Ben-Zvi commented on issue #1480: DRILL-6755: Avoid building Hash Table for inner/left join when probe side is empty
Date Thu, 27 Sep 2018 19:03:31 GMT
Ben-Zvi commented on issue #1480: DRILL-6755: Avoid building Hash Table for inner/left join
when probe side is empty
URL: https://github.com/apache/drill/pull/1480#issuecomment-425207228
 
 
   Indeed this PR only addresses the "NONE 1st" case. As for the "NONE 2nd" case (following
a 1st OK_NEW_SCHEMA) - this would open up the can of worms we saw before - early sniffing
the probe side cranks the actual execution there (e.g., another Hash Join below an Exchange)
while other parts of the query are still in schema discovery.
   
   Not sure if in all cases where an operator finds it has no data to return during schema
discovery, a NONE is returned first. Note that the NONE does have a schema (e.g., so a Right
Join can return nulls for those missing columns). Maybe we can increase the impact of this
PR by checking all these cases, and documenting/testing that our protocol allows for a NONE
to be returned first (i.e. during schema discovery).
    

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