[jira] [Closed] (DRILL-7038) Queries on partitioned columns scan the entire datasets

["Anton Gozhiy (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DRILL-7038?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Anton Gozhiy closed DRILL-7038.
-------------------------------

Verified with Drill version 1.16.0-SNAPSHOT (commit 494c2060a385408f27185949e6899a9017b6b7ff)
Cases tested:
# Group by
# Distinct
# Order by
# Presence of files aside the partition folders
# Different file formats
# Negative cases (agg functions, having clause, limit etc)

> Queries on partitioned columns scan the entire datasets
> -------------------------------------------------------
>
>                 Key: DRILL-7038
>                 URL: https://issues.apache.org/jira/browse/DRILL-7038
>             Project: Apache Drill
>          Issue Type: Improvement
>            Reporter: Bohdan Kazydub
>            Assignee: Bohdan Kazydub
>            Priority: Major
>              Labels: doc-complete, ready-to-commit
>             Fix For: 1.16.0
>
>
> For tables with hive-style partitions like
> {code}
> /table/2018/Q1
> /table/2018/Q2
> /table/2019/Q1
> etc.
> {code}
> if any of the following queries is run:
> {code}
> select distinct dir0 from dfs.`/table`
> {code}
> {code}
> select dir0 from dfs.`/table` group by dir0
> {code}
> it will actually scan every single record in the table rather than just getting a list of directories at the dir0 level. This applies even when cached metadata is available. This is a big penalty especially as the datasets grow.
> To avoid such situations, a logical prune rule can be used to collect partition columns (`dir0`), either from metadata cache (if available) or group scan, and drop unnecessary files from being read. The rule will be applied on following conditions:
> 1) all queried columns are partitoin columns, and
> 2) either {{DISTINCT}} or {{GROUP BY}} operations are performed.



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