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From "Jinfeng Ni (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DRILL-684) Use parquet row count in cost-based optimization. Use parquet row count, column value count to optimize count() aggregate function.
Date Sat, 10 May 2014 22:05:41 GMT
Jinfeng Ni created DRILL-684:
--------------------------------

             Summary: Use parquet row count in cost-based optimization.  Use parquet row count,
column value count to optimize count() aggregate function. 
                 Key: DRILL-684
                 URL: https://issues.apache.org/jira/browse/DRILL-684
             Project: Apache Drill
          Issue Type: Improvement
            Reporter: Jinfeng Ni
            Assignee: Jinfeng Ni
         Attachments: DRILL-684.1.patch

Parquet group scan provides the exact row count and the exact value count for each individual
column.  Such information could be leveraged in the following two ways:

1. Use the count in the cost estimation, when query refers parquet files.

2. Use the row count or column value count to optimize count() aggregate function.

For instance,  select count(*) from parquet_file; 
                       select count(column_a) from parquet_file;

First query could be transformed to return the row count directly, the second one could return
the column value count for 'column_a'. Both of the two cases will avoid scan the whole parquet
files, thus improve query performance. 

 



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