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Andrew Ray commented on SPARK-21330: ------------------------------------ https://github.com/apache/spark/pull/18800 > 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 > > 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} -- This message was sent by Atlassian JIRA (v6.4.14#64029) --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@spark.apache.org For additional commands, e-mail: issues-h...@spark.apache.org