Github user kayousterhout commented on a diff in the pull request:
https://github.com/apache/spark/pull/6352#discussion_r31166040
--- Diff:
core/src/test/scala/org/apache/spark/scheduler/DAGSchedulerSuite.scala ---
@@ -342,6 +342,29 @@ class DAGSchedulerSuite
assert(locs === Seq(Seq("hostA", "hostB"), Seq("hostB", "hostC"),
Seq("hostC", "hostD")))
}
+ /**
+ * +---+ shuffle +---+ +---+ +---+
+ * | A |<--------| B |<---| C |<---| D |
+ * +---+ +---+ +---+ +---+
+ * Here, D has one-to-one dependencies on C. C is derived from A by
performing a shuffle
+ * and then a map. If we're trying to determine which ancestor stages
need to be computed in
+ * order to compute D, we need to figure out whether the shuffle A -> B
should be performed.
+ * If the RDD C, which has only one ancestor via a narrow dependency, is
cached, then we won't
+ * need to compute A, even if it has some unavailable output partitions.
The same goes for B:
+ * if B is 100% cached, then we can avoid the shuffle on A.
+ */
+ test("SPARK-7826: getMissingParentStages should consider all ancestor
RDDs' cache statuses") {
+ val rddA = new MyRDD(sc, 1, Nil)
+ val rddB = new MyRDD(sc, 1, List(new ShuffleDependency(rddA, null)))
+ val rddC = new MyRDD(sc, 1, List(new OneToOneDependency(rddB))).cache()
+ val rddD = new MyRDD(sc, 1, List(new OneToOneDependency(rddC)))
+ cacheLocations(rddC.id -> 0) =
+ Seq(makeBlockManagerId("hostA"), makeBlockManagerId("hostB"))
+ submit(rddD, Array(0))
+ assert(scheduler.runningStages.size === 1)
+ assert(scheduler.runningStages.head.id === 1)
--- End diff --
(I think this is more intuitive; otherwise, it's hard for someone looking
at this to understand why the ID should be 1. This also makes the test more
agnostic to unrelated scheduler internals, like if we change the way we assign
IDs to stages)
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