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Posted to issues@spark.apache.org by "Robert Joseph Evans (Jira)" <ji...@apache.org> on 2021/04/16 21:45:00 UTC
[jira] [Commented] (SPARK-35108) Pickle produces incorrect key
labels for GenericRowWithSchema (data corruption)
[ https://issues.apache.org/jira/browse/SPARK-35108?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17324088#comment-17324088 ]
Robert Joseph Evans commented on SPARK-35108:
---------------------------------------------
If you have SPARK_HOME set when you run test.sh on a system with 6 cores or more it should reproduce the issue.
I was able to mitigate the issue by adding .equals and .hashCode to GenericRowWithSchema so it took into account the schema. But we could also try to turn off the dedupe or value compare dedupe (Pickler has options to disable these things). I am not sure what the proper fix for this would be because the code for all of these is shared with other code paths.
> Pickle produces incorrect key labels for GenericRowWithSchema (data corruption)
> -------------------------------------------------------------------------------
>
> Key: SPARK-35108
> URL: https://issues.apache.org/jira/browse/SPARK-35108
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 3.0.1, 3.0.2
> Reporter: Robert Joseph Evans
> Priority: Major
> Attachments: test.py, test.sh
>
>
> I think this also shows up for all versions of Spark that pickle the data when doing a collect from python.
> When you do a collect in python java will do a collect and convert the UnsafeRows into GenericRowWithSchema instances before it sends them to the Pickler. The Pickler, by default, will try to dedupe objects using hashCode and .equals for the object. But .equals and .hashCode for GenericRowWithSchema only looks at the data, not the schema. But when we pickle the row the keys from the schema are written out.
> This can result in data corruption, sort of, in a few cases where a row has the same number of elements as a struct within the row does, or a sub-struct within another struct.
> If the data happens to be the same, the keys for the resulting row or struct can be wrong.
> My repro case is a bit convoluted, but it does happen.
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