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Posted to issues@spark.apache.org by "Reynold Xin (JIRA)" <ji...@apache.org> on 2018/04/03 05:11:00 UTC
[jira] [Commented] (SPARK-23852) Parquet MR bug can lead to
incorrect SQL results
[ https://issues.apache.org/jira/browse/SPARK-23852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16423479#comment-16423479 ]
Reynold Xin commented on SPARK-23852:
-------------------------------------
Does turning the flag parquet.filter.stats.enabled off also turning off row group level skipping?
> 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: Critical
>
> 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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