c21 commented on a change in pull request #29277:
URL: https://github.com/apache/spark/pull/29277#discussion_r463165676
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/WholeStageCodegenExec.scala
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@@ -903,6 +904,10 @@ case class CollapseCodegenStages(
// The children of SortMergeJoin should do codegen separately.
j.withNewChildren(j.children.map(
child => InputAdapter(insertWholeStageCodegen(child))))
+ case j: ShuffledHashJoinExec =>
+ // The children of ShuffledHashJoin should do codegen separately.
+ j.withNewChildren(j.children.map(
Review comment:
@viirya - I don't think we can remove this. We have to do shuffled hash
join codegen separately, as we have [a hardcoded dependency for build side
input `input[1]` when building
relation](https://github.com/apache/spark/pull/29277/files#diff-db4ffe4f0196a9d7cf1f04c350ee3381R90).
This can go wrong if we have multiple shuffled hash join in one query.
E.g.
```
test("ShuffledHashJoin should be included in WholeStageCodegen") {
withSQLConf(SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "30",
SQLConf.SHUFFLE_PARTITIONS.key -> "2",
SQLConf.PREFER_SORTMERGEJOIN.key -> "false") {
val df1 = spark.range(5).select($"id".as("k1"))
val df2 = spark.range(15).select($"id".as("k2"))
val df3 = spark.range(6).select($"id".as("k3"))
val twoJoinsDF = df1.join(df2, $"k1" === $"k2").join(df3, $"k1" ===
$"k3")
}
}
```
If we don't codegen shuffled hash join children separately, we will get
something like:
```
/* 018 */ public void init(int index, scala.collection.Iterator[] inputs) {
/* 019 */ partitionIndex = index;
/* 020 */ this.inputs = inputs;
/* 021 */ inputadapter_input_0 = inputs[0];
/* 022 */ shj_relation_0 =
((org.apache.spark.sql.execution.joins.ShuffledHashJoinExec) references[0] /*
plan */).buildHashedRelation(inputs[1]);
/* 023 */ shj_mutableStateArray_0[0] = new
org.apache.spark.sql.catalyst.expressions.codegen.UnsafeRowWriter(2, 0);
/* 024 */ shj_relation_1 =
((org.apache.spark.sql.execution.joins.ShuffledHashJoinExec) references[2] /*
plan */).buildHashedRelation(inputs[1]);
/* 025 */ shj_mutableStateArray_0[1] = new
org.apache.spark.sql.catalyst.expressions.codegen.UnsafeRowWriter(3, 0);
/* 026 */
/* 027 */ }
```
`shj_relation_0` and `shj_relation_1` will try to build hash relation on
same input (but shouldn't), as the `input[1]` is hardcoded there. On the other
hand, I couldn't think of an alternative way not to hardcode `input[1]` here in
codegen. Let me know if you have any better options. Thanks. I also updated
`WholeStageCodegenSuite.scala` to have a unit test for this kind of multiple
joins query.
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