Minor Description
`ExtractEquiJoinKeys` is incorrectly using filter predicates as the join condition for joins. While this does not lead to incorrect results but in case of bucketed + sorted tables, we might miss out on avoiding un-necessary shuffle + sort. eg.
val df = (1 until 10).toDF("id").coalesce(1) hc.sql("DROP TABLE IF EXISTS table1").collect df.write.bucketBy(8, "id").sortBy("id").saveAsTable("table1") hc.sql("DROP TABLE IF EXISTS table2").collect df.write.bucketBy(8, "id").sortBy("id").saveAsTable("table2") sqlContext.sql(""" SELECT a.id, b.id FROM table1 a FULL OUTER JOIN table2 b ON a.id = b.id AND a.id='1' AND b.id='1' """).explain(true)
This is doing shuffle + sort over table scan outputs which is not needed as both tables are bucketed and sorted on the same columns and have same number of buckets. This should be a single stage job.
SortMergeJoin [id#38, cast(id#38 as double), 1.0], [id#39, 1.0, cast(id#39 as double)], FullOuter :- *Sort [id#38 ASC NULLS FIRST, cast(id#38 as double) ASC NULLS FIRST, 1.0 ASC NULLS FIRST], false, 0 : +- Exchange hashpartitioning(id#38, cast(id#38 as double), 1.0, 200) : +- *FileScan parquet default.table1[id#38] Batched: true, Format: ParquetFormat, InputPaths: file:spark-warehouse/table1, PartitionFilters: [], PushedFilters: [], ReadSchema: struct<id:int> +- *Sort [id#39 ASC NULLS FIRST, 1.0 ASC NULLS FIRST, cast(id#39 as double) ASC NULLS FIRST], false, 0 +- Exchange hashpartitioning(id#39, 1.0, cast(id#39 as double), 200) +- *FileScan parquet default.table2[id#39] Batched: true, Format: ParquetFormat, InputPaths: file:spark-warehouse/table2, PartitionFilters: [], PushedFilters: [], ReadSchema: struct<id:int>
