Bug: Preserve hash join (BHJ and SHJ) stream side ordering
Status: Resolved | Priority: Trivial | Resolution: Fixed
Created: 22/Jul/20 00:16
Affects Version/s: 3.1.0

Currently `BroadcastHashJoinExec` and `ShuffledHashJoinExec` do not preserve children output ordering information (inherit from `SparkPlan.outputOrdering`, which is Nil). This can add unnecessary sort in complex queries involved multiple joins.

Example:

 
{code:java}
withSQLConf(
      SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "50") {
      val df1 = spark.range(100).select($"id".as("k1"))
      val df2 = spark.range(100).select($"id".as("k2"))
      val df3 = spark.range(3).select($"id".as("k3"))
      val df4 = spark.range(100).select($"id".as("k4"))
      val plan = df1.join(df2, $"k1" === $"k2")
        .join(df3, $"k1" === $"k3")
        .join(df4, $"k1" === $"k4")
        .queryExecution
        .executedPlan
}
{code}
 

Current physical plan (extra sort on `k1` before top sort merge join):
{code:java}
*(9) SortMergeJoin [k1#220L], [k4#232L], Inner
:- *(6) Sort [k1#220L ASC NULLS FIRST], false, 0
:  +- *(6) BroadcastHashJoin [k1#220L], [k3#228L], Inner, BuildRight
:     :- *(6) SortMergeJoin [k1#220L], [k2#224L], Inner
:     :  :- *(2) Sort [k1#220L ASC NULLS FIRST], false, 0
:     :  :  +- Exchange hashpartitioning(k1#220L, 5), true, [id=#128]
:     :  :     +- *(1) Project [id#218L AS k1#220L]
:     :  :        +- *(1) Range (0, 100, step=1, splits=2)
:     :  +- *(4) Sort [k2#224L ASC NULLS FIRST], false, 0
:     :     +- Exchange hashpartitioning(k2#224L, 5), true, [id=#134]
:     :        +- *(3) Project [id#222L AS k2#224L]
:     :           +- *(3) Range (0, 100, step=1, splits=2)
:     +- BroadcastExchange HashedRelationBroadcastMode(List(input[0, bigint, false])), [id=#141]
:        +- *(5) Project [id#226L AS k3#228L]
:           +- *(5) Range (0, 3, step=1, splits=2)
+- *(8) Sort [k4#232L ASC NULLS FIRST], false, 0
   +- Exchange hashpartitioning(k4#232L, 5), true, [id=#148]
      +- *(7) Project [id#230L AS k4#232L]
         +- *(7) Range (0, 100, step=1, splits=2)
{code}
Ideal physical plan (no extra sort on `k1` before top sort merge join):
{code:java}
*(9) SortMergeJoin [k1#220L], [k4#232L], Inner
:- *(6) BroadcastHashJoin [k1#220L], [k3#228L], Inner, BuildRight
:  :- *(6) SortMergeJoin [k1#220L], [k2#224L], Inner
:  :  :- *(2) Sort [k1#220L ASC NULLS FIRST], false, 0
:  :  :  +- Exchange hashpartitioning(k1#220L, 5), true, [id=#127]
:  :  :     +- *(1) Project [id#218L AS k1#220L]
:  :  :        +- *(1) Range (0, 100, step=1, splits=2)
:  :  +- *(4) Sort [k2#224L ASC NULLS FIRST], false, 0
:  :     +- Exchange hashpartitioning(k2#224L, 5), true, [id=#133]
:  :        +- *(3) Project [id#222L AS k2#224L]
:  :           +- *(3) Range (0, 100, step=1, splits=2)
:  +- BroadcastExchange HashedRelationBroadcastMode(List(input[0, bigint, false])), [id=#140]
:     +- *(5) Project [id#226L AS k3#228L]
:        +- *(5) Range (0, 3, step=1, splits=2)
+- *(8) Sort [k4#232L ASC NULLS FIRST], false, 0
   +- Exchange hashpartitioning(k4#232L, 5), true, [id=#146]
      +- *(7) Project [id#230L AS k4#232L]
         +- *(7) Range (0, 100, step=1, splits=2){code}