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From "Jinfeng Ni (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-4589) Reduce planning time for file system partition pruning by reducing filter evaluation overhead
Date Wed, 06 Apr 2016 23:05:25 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4589?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15229298#comment-15229298
] 

Jinfeng Ni commented on DRILL-4589:
-----------------------------------

I have a patch for this JIRA. Using the same dataset used in the comparison done in DRILL-2517(With
115k parquet files in total, it's organized in 25 directories (1990, 1991, ... ), and each
directory has four subdirectories (Q1, Q2, Q3, Q4).), here is the query planning time measured
on a mac laptop. 

{code}
explain plan for select * from dfs.`/drill/testdata/tpch-sf10/lineitem115k` where dir0 = '1990'
and dir1 = 'Q1';
{code}

Without the patch (on today's master branch:
{code}
1 row selected (8.084 seconds)
{code}

With the patch
{code}
1 row selected (4.306 seconds)
{code}

If the partition filter contains complex expression, then the improvement percentage is even
higher. For this query, the improvement is 24.951 seconds vs. 4.393 seconds
{code}
explain plan for select * from dfs.`/drill/testdata/tpch-sf10/lineitem115k` where concat(substr(dir0,
1, 4), substr(dir1, 1, 2)) = '1990Q1';
{code} 




> Reduce planning time for file system partition pruning by reducing filter evaluation
overhead
> ---------------------------------------------------------------------------------------------
>
>                 Key: DRILL-4589
>                 URL: https://issues.apache.org/jira/browse/DRILL-4589
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Query Planning & Optimization
>            Reporter: Jinfeng Ni
>            Assignee: Jinfeng Ni
>
> When Drill is used to query hundreds of thousands, or even millions of files organized
into multi-level directories, user typically will provide a partition filter like  : dir0
= something and dir1 = something2 and .. .  
> For such queries, we saw the query planning time could be unacceptable long, due to three
main overheads: 1) to expand and get the list of files, 2) to evaluate the partition filter,
3) to get the metadata, in the case of parquet files for which metadata cache file is not
available. 
> DRILL-2517 targets at the 3rd part of overhead. As a follow-up work after DRILL-2517,
we plan to reduce the filter evaluation overhead. For now, the partition filter evaluation
is applied to file level. In many cases, we saw that the number of leaf subdirectories is
significantly lower than that of files. Since all the files under the same leaf subdirecctory
share the same directory metadata, we should apply the filter evaluation at the leaf subdirectory.
By doing that, we could reduce the cpu overhead to evaluate the filter, and the memory overhead
as well.



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