c21 opened a new pull request #29181:
URL: https://github.com/apache/spark/pull/29181
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### What changes were proposed in this pull request?
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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:
```
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
}
```
Current physical plan (extra sort on `k1` before top sort merge join):
```
*(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)
```
Ideal physical plan (no extra sort on `k1` before top sort merge join):
```
*(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)
```
### Why are the changes needed?
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To avoid unnecessary sort in query, and it has most impact when users read
sorted bucketed table.
Though the unnecessary sort is operating on already sorted data, it would
have obvious negative impact on IO and query run time if the data is large and
external sorting happens.
### Does this PR introduce _any_ user-facing change?
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the documentation fix.
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No.
### How was this patch tested?
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Added unit test in `JoinSuite`.
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