Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/16925#discussion_r101124529
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/SubstituteHints.scala
---
@@ -0,0 +1,103 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.analysis
+
+import org.apache.spark.sql.catalyst.CatalystConf
+import org.apache.spark.sql.catalyst.plans.logical._
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.catalyst.trees.CurrentOrigin
+
+
+/**
+ * Collection of rules related to hints. The only hint currently available
is broadcast join hint.
+ *
+ * Note that this is separatedly into two rules because in the future we
might introduce new hint
+ * rules that have different ordering requirements from broadcast.
+ */
+object SubstituteHints {
+
+ /**
+ * Substitute Hints.
+ *
+ * The only hint currently available is broadcast join hint.
+ *
+ * For broadcast hint, we accept "BROADCAST", "BROADCASTJOIN", and
"MAPJOIN", and a sequence of
+ * relation aliases can be specified in the hint. A broadcast hint plan
node will be inserted
+ * on top of any relation (that is not aliased differently), subquery,
or common table expression
+ * that match the specified name.
+ *
+ * The hint resolution works by recursively traversing down the query
plan to find a relation or
+ * subquery that matches one of the specified broadcast aliases. The
traversal does not go past
+ * beyond any existing broadcast hints, subquery aliases.
+ *
+ * This rule must happen before common table expressions.
+ */
+ class SubstituteBroadcastHints(conf: CatalystConf) extends
Rule[LogicalPlan] {
+ private val BROADCAST_HINT_NAMES = Set("BROADCAST", "BROADCASTJOIN",
"MAPJOIN")
+
+ def resolver: Resolver = conf.resolver
+
+ private def applyBroadcastHint(plan: LogicalPlan, toBroadcast:
Set[String]): LogicalPlan = {
+ // Whether to continue recursing down the tree
+ var recurse = true
+
+ val newNode = CurrentOrigin.withOrigin(plan.origin) {
+ plan match {
+ case r: UnresolvedRelation =>
+ val alias = r.alias.getOrElse(r.tableIdentifier.table)
+ if (toBroadcast.exists(resolver(_, alias)))
BroadcastHint(plan) else plan
+ case r: SubqueryAlias =>
+ if (toBroadcast.exists(resolver(_, r.alias))) {
+ BroadcastHint(plan)
+ } else {
+ // Don't recurse down subquery aliases if there are no match.
+ recurse = false
+ plan
+ }
+ case _: BroadcastHint =>
+ // Found a broadcast hint; don't change the plan but also
don't recurse down.
+ recurse = false
+ plan
+ case _ =>
+ plan
+ }
+ }
+
+ if ((plan fastEquals newNode) && recurse) {
+ newNode.mapChildren(child => applyBroadcastHint(child,
toBroadcast))
+ } else {
+ newNode
+ }
+ }
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
+ case h: Hint if BROADCAST_HINT_NAMES.contains(h.name.toUpperCase) =>
+ applyBroadcastHint(h.child, h.parameters.toSet)
+ }
+ }
+
+ /**
+ * Removes all the hints. This must be executed after all the other hint
rules are executed.
--- End diff --
shall we mention that, this can happen when users specify invalid hints and
we will ignore it?
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