cloud-fan 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_r283195657
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File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/CacheManager.scala
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@@ -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.
Review comment:
It doesn't matter, because
1. as a cache key, the lookup relies on `semanticEquals`, so having the hint
node in the plan has no effect.
2. the cache lookup returns `InMemoryRelation`, which has no hint.
I think the behavior is pretty clear: for any query, the hint behavior
should be the same no matter some sub-plans are cached or not.
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