[jira] [Resolved] (DRILL-684) Use parquet row count in cost-based optimization. Use parquet row count, column value count to optimize count() aggregate function.

["Jacques Nadeau (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DRILL-684?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jacques Nadeau resolved DRILL-684.
----------------------------------

    Resolution: Fixed

added in cf2b888

> 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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