maryannxue commented on a change in pull request #24164: [SPARK-27225][SQL]
Implement join strategy hints
URL: https://github.com/apache/spark/pull/24164#discussion_r272667459
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/EliminateResolvedHint.scala
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@@ -40,17 +40,16 @@ object EliminateResolvedHint extends Rule[LogicalPlan] {
}
private def mergeHints(hints: Seq[HintInfo]): Option[HintInfo] = {
- hints.reduceOption((h1, h2) => HintInfo(
- broadcast = h1.broadcast || h2.broadcast))
+ hints.reduceOption((h1, h2) => h1.merge(h2))
Review comment:
There is no behavior change here. There cannot be, coz we only had one hint
before this PR, so a broadcast + broadcast = broadcast. The new behavior is
defined in the description of this PR:
> Conflicts within either side of the join: take the first strategy hint
specified in the query, or the top hint node in Dataset. For example, in
"select /*+ merge(t1) / /+ broadcast(t1) */ k1, v2 from t1 join t2 on t1.k1 =
t2.k2", take "merge(t1)"; in df1.hint("merge").hint("shuffle_hash").join(df2),
take "shuffle_hash". This is a general hint conflict resolving strategy, not
specific to join strategy hint.
The merge function is implemented in HintInfo, which should be responsible
for deciding the strategy of merging hints between a node on top and a node on
the bottom.
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