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From jinfengni <...@git.apache.org>
Subject [GitHub] drill pull request: DRILL-4387: GroupScan or ScanBatchCreator shou...
Date Thu, 18 Feb 2016 18:49:17 GMT
Github user jinfengni commented on a diff in the pull request:

    https://github.com/apache/drill/pull/379#discussion_r53361870
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/ParquetScanBatchCreator.java
---
    @@ -87,9 +87,6 @@ public ScanBatch getBatch(FragmentContext context, ParquetRowGroupScan
rowGroupS
               newColumns.add(column);
             }
           }
    -      if (newColumns.isEmpty()) {
    --- End diff --
    
    I went through all the ScanBatchCreator in Drill's code base. Seems ParquetScanBatchCreator
is the only one that is converting an empty column list to ALL_COLUMNS. Looking at the history,
seems DRILL-1845 added the code, probably just to make it work in parquet for skipAll query.
 
    
    With the patch of DRILL-4279, parquet record reader would be able to handle empty column
list. 
    
    Besides ParquetScanBatchCreator, this patch also modifies HBaseGroupScan, EasyGroupScan
where it originally interprets empty column lists into ALL_COLUMNS. 
    
    I'll add some comment to the code to clarify the different meaning of NULL and empty column
list. 



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