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From "Jason Altekruse (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-4308) Aggregate operations on dir<N> columns can be more efficient for certain use cases
Date Tue, 26 Jan 2016 03:37:39 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4308?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15116604#comment-15116604

Jason Altekruse commented on DRILL-4308:

[~amansinha100] One of these queries is possible today, the other should be simple to implement
by exposing the same information given in "show files" command in a way that can have a filter
applied to it (today it isn't really a query, it's a special case). As show files includes
a field isDirectory, this should be as simple as apply a filter to this data.

the first can be written as: select dir0 from largetable where dir0 = maxdir() limit 1

> Aggregate operations on dir<N> columns can be more efficient for certain use cases
> ----------------------------------------------------------------------------------
>                 Key: DRILL-4308
>                 URL: https://issues.apache.org/jira/browse/DRILL-4308
>             Project: Apache Drill
>          Issue Type: Improvement
>          Components: Execution - Relational Operators
>    Affects Versions: 1.4.0
>            Reporter: Aman Sinha
> For queries that perform plain aggregates or DISTINCT operations on the directory partition
columns (dir0, dir1 etc.) and there are no other columns referenced in the query, the performance
could be substantially improved by not having to scan the entire dataset.   
> Consider the following types of queries:
> {noformat}
> select  min(dir0) from largetable;
> select  distinct dir0 from largetable;
> {noformat}
> The number of distinct values of dir<N> columns is typically quite small and there's
no reason to scan the large table.  This is also come as user feedback from some Drill users.
 Of course, if there's any other column referenced in the query (WHERE, ORDER-BY etc.) then
we cannot apply this optimization.  

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