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Posted to issues@spark.apache.org by "Russell Spitzer (JIRA)" <ji...@apache.org> on 2016/09/26 23:43:20 UTC
[jira] [Created] (SPARK-17673) Reused Exchange Aggregations Produce
Incorrect Results
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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