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https://issues.apache.org/jira/browse/SPARK-21330?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen reassigned SPARK-21330:
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Assignee: Andrew Ray
> Bad partitioning does not allow to read a JDBC table with extreme values on
> the partition column
> ------------------------------------------------------------------------------------------------
>
> Key: SPARK-21330
> URL: https://issues.apache.org/jira/browse/SPARK-21330
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.1.1
> Reporter: Stefano Parmesan
> Assignee: Andrew Ray
> Fix For: 2.1.2, 2.2.1, 2.3.0
>
>
> When using "extreme" values in the partition column (like having a randomly
> generated long number) overflow might happen, leading to the following
> warning message:
> {code}WARN JDBCRelation: The number of partitions is reduced because the
> specified number of partitions is less than the difference between upper
> bound and lower bound. Updated number of partitions: -1559072469251914524;
> Input number of partitions: 20; Lower bound: -7701345953623242445; Upper
> bound: 9186325650834394647.{code}
> When this happens, no data is read from the table.
> This happens because of the following check in
> {{org/apache/spark/sql/execution/datasources/jdbc/JDBCRelation.scala}}:
> {code}if ((upperBound - lowerBound) >= partitioning.numPartitions){code}
> Funny thing is that we worry about overflows a few lines later:
> {code} // Overflow and silliness can happen if you subtract then divide.
> // Here we get a little roundoff, but that's (hopefully) OK.{code}
> A better check would be:
> {code}if ((upperBound - partitioning.numPartitions) >= lowerBound){code}
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