cloud-fan commented on a change in pull request #26409: [SPARK-29655][SQL] Read
bucketed tables obeys spark.sql.shuffle.partitions
URL: https://github.com/apache/spark/pull/26409#discussion_r346306732
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/EnsureRequirements.scala
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@@ -83,7 +83,19 @@ case class EnsureRequirements(conf: SQLConf) extends
Rule[SparkPlan] {
numPartitionsSet.headOption
}
- val targetNumPartitions =
requiredNumPartitions.getOrElse(childrenNumPartitions.max)
+ // Read bucketed tables always obeys numShufflePartitions because
maxNumPostShufflePartitions
+ // is usually much larger than numShufflePartitions,
+ // which causes some bucket map join lose efficacy after enabling
adaptive execution.
Review comment:
The comment is hard to understand. How about
```
If there are non-shuffle children that satisfy the required distribution, we
have some tradeoffs
when picking the expected number of shuffle partitions:
1. we should avoid shuffling these children
2. we should have a reasonable parallelism
Here we pick the max number of partitions among these non-shuffle children
as the expected number
of shuffle partitions. However, if it's smaller than
`conf.numShufflePartitions`, we pick
`conf.numShufflePartitions` as the expected number of shuffle partitions.
```
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