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From "Wenchen Fan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-25206) wrong records are returned when Hive metastore schema and parquet schema are in different letter cases
Date Wed, 31 Oct 2018 16:23:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-25206?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16670339#comment-16670339
] 

Wenchen Fan commented on SPARK-25206:
-------------------------------------

marked it as resolved in 2.4.0, since the test is already in 2.4.0 and passes.

> wrong records are returned when Hive metastore schema and parquet schema are in different
letter cases
> ------------------------------------------------------------------------------------------------------
>
>                 Key: SPARK-25206
>                 URL: https://issues.apache.org/jira/browse/SPARK-25206
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 2.2.2, 2.3.1
>            Reporter: yucai
>            Priority: Blocker
>              Labels: Parquet, correctness, known_issue
>             Fix For: 2.4.0
>
>         Attachments: image-2018-08-24-18-05-23-485.png, image-2018-08-24-22-33-03-231.png,
image-2018-08-24-22-34-11-539.png, image-2018-08-24-22-46-05-346.png, image-2018-08-25-09-54-53-219.png,
image-2018-08-25-10-04-21-901.png, pr22183.png
>
>
> In current Spark 2.3.1, below query returns wrong data silently.
> {code:java}
> spark.range(10).write.parquet("/tmp/data")
> sql("DROP TABLE t")
> sql("CREATE TABLE t (ID LONG) USING parquet LOCATION '/tmp/data'")
> scala> sql("select * from t where id > 0").show
> +---+
> | ID|
> +---+
> +---+
> {code}
>  
> *Root Cause*
> After deep dive, it has two issues, both are related to different letter cases between
Hive metastore schema and parquet schema.
> 1. Wrong column is pushdown.
> Spark pushdowns FilterApi.gt(intColumn("{color:#ff0000}ID{color}"), 0: Integer) into
parquet, but {color:#ff0000}ID{color} does not exist in /tmp/data (parquet is case sensitive,
it has {color:#ff0000}id{color} actually).
> So no records are returned.
> Since SPARK-24716, Spark uses Parquet schema instead of Hive metastore schema to do the
pushdown, perfect for this issue.
> 2. Spark SQL returns NULL for a column whose Hive metastore schema and Parquet schema
are in different letter cases, even spark.sql.caseSensitive set to false.
> SPARK-25132 addressed this issue already.
>  
> The biggest difference is, in Spark 2.1, user will get Exception for the same query:
> {code:java}
> Caused by: java.lang.IllegalArgumentException: Column [ID] was not found in schema!{code}
> So they will know the issue and fix the query.
> But in Spark 2.3, user will get the wrong results sliently.
>  
> To make the above query work, we need both SPARK-25132 and -SPARK-24716.-
>  
> [~yumwang] , [~cloud_fan], [~smilegator], any thoughts? Should we backport it?



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