LantaoJin commented on a change in pull request #24245:
[SPARK-13704][CORE][YARN] Reduce rack resolution time
URL: https://github.com/apache/spark/pull/24245#discussion_r271265748
##########
File path:
resource-managers/yarn/src/main/scala/org/apache/spark/deploy/yarn/SparkRackResolver.scala
##########
@@ -17,24 +17,105 @@
package org.apache.spark.deploy.yarn
+import scala.collection.JavaConverters._
+import scala.collection.mutable.ArrayBuffer
+
+import com.google.common.base.Strings
import org.apache.hadoop.conf.Configuration
+import org.apache.hadoop.fs.CommonConfigurationKeysPublic
+import org.apache.hadoop.net._
+import org.apache.hadoop.util.ReflectionUtils
import org.apache.hadoop.yarn.util.RackResolver
import org.apache.log4j.{Level, Logger}
+import org.apache.spark.internal.Logging
+
/**
- * Wrapper around YARN's [[RackResolver]]. This allows Spark tests to easily
override the
+ * Re-implement YARN's [[RackResolver]]. This allows Spark tests to easily
override the
* default behavior, since YARN's class self-initializes the first time it's
called, and
* future calls all use the initial configuration.
*/
-private[yarn] class SparkRackResolver {
+private[spark] class SparkRackResolver(conf: Configuration) extends Logging {
// RackResolver logs an INFO message whenever it resolves a rack, which is
way too often.
if (Logger.getLogger(classOf[RackResolver]).getLevel == null) {
Logger.getLogger(classOf[RackResolver]).setLevel(Level.WARN)
}
- def resolve(conf: Configuration, hostName: String): String = {
- RackResolver.resolve(conf, hostName).getNetworkLocation()
+ private val dnsToSwitchMapping: DNSToSwitchMapping = {
+ val dnsToSwitchMappingClass =
+
conf.getClass(CommonConfigurationKeysPublic.NET_TOPOLOGY_NODE_SWITCH_MAPPING_IMPL_KEY,
+ classOf[ScriptBasedMapping], classOf[DNSToSwitchMapping])
+ ReflectionUtils.newInstance(dnsToSwitchMappingClass, conf)
+ .asInstanceOf[DNSToSwitchMapping] match {
+ case c: CachedDNSToSwitchMapping => c
+ case o => new CachedDNSToSwitchMapping(o)
+ }
+ }
+
+ def resolve(hostName: String): String = {
+ coreResolve(Seq(hostName)).head.getNetworkLocation
+ }
+
+ /**
+ * Added in SPARK-13704.
+ * This should be changed to `RackResolver.resolve(conf, hostNames)`
+ * in hadoop releases with YARN-9332.
+ */
+ def resolve(hostNames: Seq[String]): Seq[Node] = {
+ coreResolve(hostNames)
+ }
+
+ private def coreResolve(hostNames: Seq[String]): Seq[Node] = {
+ val nodes = new ArrayBuffer[Node]
+ // dnsToSwitchMapping is thread-safe
+ val rNameList = dnsToSwitchMapping.resolve(hostNames.toList.asJava).asScala
+ if (rNameList == null || rNameList.isEmpty) {
+ hostNames.foreach(nodes += new NodeBase(_, NetworkTopology.DEFAULT_RACK))
+ logInfo(s"Got an error when resolving hostNames. " +
+ s"Falling back to ${NetworkTopology.DEFAULT_RACK} for all")
+ } else {
+ for ((hostName, rName) <- hostNames.zip(rNameList)) {
+ if (Strings.isNullOrEmpty(rName)) {
+ nodes += new NodeBase(hostName, NetworkTopology.DEFAULT_RACK)
+ logDebug(s"Could not resolve $hostName. " +
+ s"Falling back to ${NetworkTopology.DEFAULT_RACK}")
+ } else {
+ nodes += new NodeBase(hostName, rName)
+ }
+ }
+ }
+ nodes.toList
+ }
+}
+
+/**
+ * Utility to resolve the rack for hosts in an efficient manner.
+ * It will cache the rack for individual hosts to avoid
+ * repeatedly performing the same expensive lookup.
+ *
+ * Its logic refers [[org.apache.hadoop.yarn.util.RackResolver]] and enhanced.
+ * This will be unnecessary in hadoop releases with YARN-9332.
+ * With that, we could just directly use
[[org.apache.hadoop.yarn.util.RackResolver]].
+ * In the meantime, this is a re-implementation for spark's use.
+ */
+object SparkRackResolver extends Logging {
+ @volatile private var instance: SparkRackResolver = _
+
+ /**
+ * It will return the static resolver instance. If there is already an
instance, the passed
+ * conf is entirely ignored. If there is not a shared instance, it will
create one with the
+ * given conf.
Review comment:
Should we explain how to instantiate a separate resolver with a separate
config here?
> Instantiate a separate resolver with a separate config by `new
SparkRackResolver(conf)`
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