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From "Apache Spark (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-23852) Parquet MR bug can lead to incorrect SQL results
Date Wed, 09 May 2018 19:11:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-23852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16469330#comment-16469330
] 

Apache Spark commented on SPARK-23852:
--------------------------------------

User 'henryr' has created a pull request for this issue:
https://github.com/apache/spark/pull/21284

> Parquet MR bug can lead to incorrect SQL results
> ------------------------------------------------
>
>                 Key: SPARK-23852
>                 URL: https://issues.apache.org/jira/browse/SPARK-23852
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 2.3.0
>            Reporter: Henry Robinson
>            Priority: Blocker
>              Labels: correctness
>
> Parquet MR 1.9.0 and 1.8.2 both have a bug, PARQUET-1217, that means that pushing certain
predicates to Parquet scanners can return fewer results than they should.
> The bug triggers in Spark when:
>  * The Parquet file being scanner has stats for the null count, but not the max or min
on the column with the predicate (Apache Impala writes files like this).
>  * The vectorized Parquet reader path is not taken, and the parquet-mr reader is used.
>  * A suitable <, <=, > or >= predicate is pushed down to Parquet.
> The bug is that the parquet-mr interprets the max and min of a row-group's column as
0 in the absence of stats. So {{col > 0}} will filter all results, even if some are >
0.
> There is no upstream release of Parquet that contains the fix for PARQUET-1217, although
a 1.10 release is planned.
> The least impactful workaround is to set the Parquet configuration {{parquet.filter.stats.enabled}}
to {{false}}.



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