squito commented on a change in pull request #23951: [SPARK-27038][CORE][YARN]
Re-implement RackResolver to reduce resolving time
URL: https://github.com/apache/spark/pull/23951#discussion_r264303212
##########
File path:
core/src/test/scala/org/apache/spark/scheduler/TaskSetManagerSuite.scala
##########
@@ -69,18 +69,48 @@ class FakeDAGScheduler(sc: SparkContext, taskScheduler:
FakeTaskScheduler)
// Get the rack for a given host
object FakeRackUtil {
private val hostToRack = new mutable.HashMap[String, String]()
+ var loopCount = 0
def cleanUp() {
hostToRack.clear()
+ loopCount = 0
}
def assignHostToRack(host: String, rack: String) {
hostToRack(host) = rack
}
def getRackForHost(host: String): Option[String] = {
+ loopCount = simulateRunResolveCommand(Seq(host))
hostToRack.get(host)
}
+
+ def getRacksForHosts(hosts: List[String]): List[Option[String]] = {
+ loopCount = simulateRunResolveCommand(hosts)
+ hosts.map(hostToRack.get)
+ }
+
+ /**
+ * This is a simulation of building and executing the resolution command.
+ * Simulate function `runResolveCommand()` in
[[org.apache.hadoop.net.ScriptBasedMapping]].
+ * If Seq has 100 elements, it returns 4. If Seq has 1 elements, it returns
1.
+ * @param args a list of arguments
+ * @return script execution times
+ */
+ private def simulateRunResolveCommand(args: Seq[String]): Int = {
+ val maxArgs = 30 // Simulate NET_TOPOLOGY_SCRIPT_NUMBER_ARGS_DEFAULT
+ var numProcessed = 0
+ var loopCount = 0
+ while (numProcessed != args.size) {
+ var start = maxArgs * loopCount
+ numProcessed = start
+ while (numProcessed < (start + maxArgs) && numProcessed < args.size) {
+ numProcessed += 1
+ }
+ loopCount += 1
+ }
+ loopCount
Review comment:
> Why I added this complexity code for UT is that after applied this patch,
the initializing processing of TaskSetManager won't invoke getRackForHost() any
more. It has no place to count invocations for getRackForHost() vs counts of
getRacksForHosts()
Just count the invocations in `FakeRackUtil.getRackForHost()` etc.
```scala
object FakeRackUtil {
...
def getRackForHost(host: String): Option[String] = {
getRackForHostCount += 1
hostToRack.get(host)
}
...
test("SPARK-27038 Verify the rack resolving time has been reduced") {
FakeRackUtil.getRackForHostCount = 0
FakeRackUtil.getRackForHostsCount = 0
...
assert(FakeRackUtil.getRackForHostCount === 0)
assert(FakeRackUtil.getRackForHostsCount === 1)
}
```
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