sunchao commented on issue #1652:
URL: 
https://github.com/apache/arrow-datafusion/issues/1652#issuecomment-1023620113


   > It will (in version after 8.0.0) preserve dictionary encoding (meaning the 
output of a dictionary encoded column will also be dictionary encoded) which 
should be a large win for low cardinality columns
   
   This is nice 👍 . By dictionary-based row group filtering I mean we can first 
decode only the dictionary pages for the column chunks where pushed down 
predicates (e.g., in predicate) are associated to, and skip the whole row group 
if no keys in the dictionary match.


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