[GitHub] [spark] maryannxue commented on a change in pull request #24580: [SPARK-27674][SQL] the hint should not be dropped after cache lookup

[GitBox <gi...@apache.org>]

maryannxue commented on a change in pull request #24580: [SPARK-27674][SQL] the hint should not be dropped after cache lookup
URL: https://github.com/apache/spark/pull/24580#discussion_r283080983
 
 

 ##########
 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/CacheManager.scala
 ##########
 @@ -212,17 +213,18 @@ class CacheManager extends Logging {
   def useCachedData(plan: LogicalPlan): LogicalPlan = {
     val newPlan = plan transformDown {
       case command: IgnoreCachedData => command
-      // Do not lookup the cache by hint node. Hint node is special, we should ignore it when
-      // canonicalizing plans, so that plans which are same except hint can hit the same cache.
-      // However, we also want to keep the hint info after cache lookup. Here we skip the hint
-      // node, so that the returned caching plan won't replace the hint node and drop the hint info
-      // from the original plan.
-      case hint: ResolvedHint => hint
 
       case currentFragment =>
-        lookupCachedData(currentFragment)
-          .map(_.cachedRepresentation.withOutput(currentFragment.output))
-          .getOrElse(currentFragment)
+        lookupCachedData(currentFragment).map { cached =>
+          // After cache lookup, we should still keep the hints from the input plan.
+          val hints = EliminateResolvedHint.extractHintsFromPlan(currentFragment)._2
+          val cachedPlan = cached.cachedRepresentation.withOutput(currentFragment.output)
+          // The returned hint list is in top-down order. We should reverse it so that the top hint
+          // is still in the top node.
+          hints.reverse.foldLeft[LogicalPlan](cachedPlan) { case (p, hint) =>
 
 Review comment:
   I suppose hints can be lost further down in the tree by matching "canonicalized". Do we need to take care of that as well?

----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
 
For queries about this service, please contact Infrastructure at:
users@infra.apache.org


With regards,
Apache Git Services

---------------------------------------------------------------------
To unsubscribe, e-mail: reviews-unsubscribe@spark.apache.org
For additional commands, e-mail: reviews-help@spark.apache.org