Major Description
`table1` and `table2` are sorted and bucketed on columns `j` and `k` (in respective order)
This is how they are generated:
val df = (0 until 16).map(i => (i % 8, i * 2, i.toString)).toDF("i", "j", "k").coalesce(1) df.write.format("org.apache.spark.sql.hive.orc.OrcFileFormat").bucketBy(8, "j", "k").sortBy("j", "k").saveAsTable("table1") df.write.format("org.apache.spark.sql.hive.orc.OrcFileFormat").bucketBy(8, "j", "k").sortBy("j", "k").saveAsTable("table2")
Now, if join predicates are specified in query in same order as bucketing and sort order, there is no shuffle and sort.
scala> hc.sql("SET spark.sql.autoBroadcastJoinThreshold=1") scala> hc.sql("SELECT * FROM table1 a JOIN table2 b ON a.j=b.j AND a.k=b.k").explain(true) == Physical Plan == *SortMergeJoin [j#61, k#62], [j#100, k#101], Inner :- *Project [i#60, j#61, k#62] : +- *Filter (isnotnull(k#62) && isnotnull(j#61)) : +- *FileScan orc default.table1[i#60,j#61,k#62] Batched: false, Format: ORC, Location: InMemoryFileIndex[file:/table1], PartitionFilters: [], PushedFilters: [IsNotNull(k), IsNotNull(j)], ReadSchema: struct<i:int,j:int,k:string> +- *Project [i#99, j#100, k#101] +- *Filter (isnotnull(j#100) && isnotnull(k#101)) +- *FileScan orc default.table2[i#99,j#100,k#101] Batched: false, Format: ORC, Location: InMemoryFileIndex[file:/table2], PartitionFilters: [], PushedFilters: [IsNotNull(j), IsNotNull(k)], ReadSchema: struct<i:int,j:int,k:string>
The same query with join predicates in different order from bucketing and sort order leads to extra shuffle and sort being introduced
scala> hc.sql("SET spark.sql.autoBroadcastJoinThreshold=1") scala> hc.sql("SELECT * FROM table1 a JOIN table2 b ON a.k=b.k AND a.j=b.j ").explain(true) == Physical Plan == *SortMergeJoin [k#62, j#61], [k#101, j#100], Inner :- *Sort [k#62 ASC NULLS FIRST, j#61 ASC NULLS FIRST], false, 0 : +- Exchange hashpartitioning(k#62, j#61, 200) : +- *Project [i#60, j#61, k#62] : +- *Filter (isnotnull(k#62) && isnotnull(j#61)) : +- *FileScan orc default.table1[i#60,j#61,k#62] Batched: false, Format: ORC, Location: InMemoryFileIndex[file:/table1], PartitionFilters: [], PushedFilters: [IsNotNull(k), IsNotNull(j)], ReadSchema: struct<i:int,j:int,k:string> +- *Sort [k#101 ASC NULLS FIRST, j#100 ASC NULLS FIRST], false, 0 +- Exchange hashpartitioning(k#101, j#100, 200) +- *Project [i#99, j#100, k#101] +- *Filter (isnotnull(j#100) && isnotnull(k#101)) +- *FileScan orc default.table2[i#99,j#100,k#101] Batched: false, Format: ORC, Location: InMemoryFileIndex[file:/table2], PartitionFilters: [], PushedFilters: [IsNotNull(j), IsNotNull(k)], ReadSchema: struct<i:int,j:int,k:string>
