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From "Russell Spitzer (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SPARK-17673) Reused Exchange Aggregations Produce Incorrect Results
Date Mon, 26 Sep 2016 23:43:20 GMT
Russell Spitzer created SPARK-17673:
---------------------------------------

             Summary: Reused Exchange Aggregations Produce Incorrect Results
                 Key: SPARK-17673
                 URL: https://issues.apache.org/jira/browse/SPARK-17673
             Project: Spark
          Issue Type: Bug
          Components: SQL
    Affects Versions: 2.0.0, 2.0.1
            Reporter: Russell Spitzer


https://datastax-oss.atlassian.net/browse/SPARKC-429

Was brought to my attention where the following code produces incorrect results

{code}
 val data = List(TestData("A", 1, 7))
    val frame = session.sqlContext.createDataFrame(session.sparkContext.parallelize(data))

    frame.createCassandraTable(
      keySpaceName,
      table,
      partitionKeyColumns = Some(Seq("id")))

    frame
      .write
      .format("org.apache.spark.sql.cassandra")
      .mode(SaveMode.Append)
      .options(Map("table" -> table, "keyspace" -> keySpaceName))
      .save()

val loaded = sparkSession.sqlContext
  .read
  .format("org.apache.spark.sql.cassandra")
  .options(Map("table" -> table, "keyspace" -> ks))
  .load()
  .select("id", "col1", "col2")
val min1 = loaded.groupBy("id").agg(min("col1").as("min"))
val min2 = loaded.groupBy("id").agg(min("col2").as("min"))
 min1.union(min2).show()
    /* prints:
      +---+---+
      | id|min|
      +---+---+
      |  A|  1|
      |  A|  1|
      +---+---+
     Should be 
      | A| 1|
      | A| 7|
     */
{code}

I looked into the explain pattern and saw 
{code}
Union
:- *HashAggregate(keys=[id#93], functions=[min(col1#94)])
:  +- Exchange hashpartitioning(id#93, 200)
:     +- *HashAggregate(keys=[id#93], functions=[partial_min(col1#94)])
:        +- *Scan org.apache.spark.sql.cassandra.CassandraSourceRelation@7ec20844 [id#93,col1#94]
+- *HashAggregate(keys=[id#93], functions=[min(col2#95)])
   +- ReusedExchange [id#93, min#153], Exchange hashpartitioning(id#93, 200)
{code}

Which was different than using a parallelized collection as the DF backing. So I tested the
same code with a Parquet backed DF and saw the same results.

{code}
    frame.write.parquet("garbagetest")
    val parquet = sparkSession.read.parquet("garbagetest").select("id", "col1", "col2")
    println("PDF")
    parquetmin1.union(parquetmin2).explain()
    parquetmin1.union(parquetmin2).show()
    /* prints:
      +---+---+
      | id|min|
      +---+---+
      |  A|  1|
      |  A|  1|
      +---+---+
*/
{code}

Which leads me to believe there is something wrong with the reused exchange. 



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