Github user sryza commented on a diff in the pull request:
https://github.com/apache/spark/pull/6394#discussion_r35152962
--- Diff:
yarn/src/main/scala/org/apache/spark/deploy/yarn/ContainerPlacementStrategy.scala
---
@@ -0,0 +1,196 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.deploy.yarn
+
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.hadoop.conf.Configuration
+import org.apache.hadoop.yarn.util.RackResolver
+
+import org.apache.spark.SparkConf
+
+private[yarn] case class ContainerLocalityPreferences(nodes:
Array[String], racks: Array[String])
+
+private[yarn] trait ContainerPlacementStrategy {
+
+ /**
+ * Calculate each container's node locality and rack locality
+ * @param numContainer number of containers to calculate
+ * @param numLocalityAwarePendingTasks number of locality required
pending tasks
+ * @param hostToLocalTaskCount a map to store the preferred hostname and
possible task
+ * numbers running on it, used as hints for
container allocation
+ * @return node localities and rack localities, each locality is an
array of string,
+ * the length of localities is the same as number of containers
+ */
+ def localityOfRequestedContainers(
+ numContainer: Int,
+ numLocalityAwarePendingTasks: Int,
+ hostToLocalTaskCount: Map[String, Int]
+ ): Array[ContainerLocalityPreferences]
+}
+
+/**
+ * This strategy is calculating the optimal locality preferences of YARN
containers by considering
+ * the node ratio of pending tasks, number of required cores/containers
and and locality of current
+ * existed containers. The target of this algorithm is to maximize the
number of tasks that
+ * would run locally.
+ *
+ * The details of this algorithm is described as below, if we have 20
tasks which
+ * require (host1, host2, host3) and 10 tasks which require (host1, host2,
host4),
+ * besides each container has 2 cores and cpus per task is 1, so the
required container number is
+ * 15, and host ratio is (host1: 30, host2: 30, host3: 20, host4: 10).
+ *
+ * 1. If requested container number (18) is more than the required
container number (15):
+ *
+ * requests for 5 containers with nodes: (host1, host2, host3, host4)
+ * requests for 5 containers with nodes: (host1, host2, host3)
+ * requests for 5 containers with nodes: (host1, host2)
+ * requests for 3 containers with no locality preferences.
+ *
+ * The placement ratio is 3 : 3 : 2 : 1, and set the additional containers
with no locality
+ * preferences.
+ *
+ * 2. If requested container number (10) is less than or equal to the
required container number
+ * (15):
+ *
+ * requests for 4 containers with nodes: (host1, host2, host3, host4)
+ * requests for 3 containers with nodes: (host1, host2, host3)
+ * requests for 3 containers with nodes: (host1, host2)
+ *
+ * The placement ratio is 10 : 10 : 7 : 4, close to expected ratio (3 : 3
: 2 : 1)
+ *
+ * 3. If containers are existed but no matching localities, follow the
method of 1 and 2.
+ *
+ * 4. If containers are existed and some localities are matched. For
example if we have 1
+ * containers on each node (host1: 1, host2: 1: host3: 1, host4: 1), and
the expected containers
+ * on each node would be (host1: 5, host2: 5, host3: 4, host4: 2),
+ * so the newly requested containers on each node would be updated to
(host1: 4, host2: 4,
+ * host3: 3, host4: 1), 12 containers by total.
+ *
+ * 4.1 If requested container number (18) is more than newly required
containers (12). Follow
+ * method 1 with updated ratio 4 : 4 : 3 : 1.
+ *
+ * 4.2 If request container number (10) is more than newly required
containers (12). Follow
+ * method 2 with updated ratio 4 : 4 : 3 : 1.
+ *
+ * 5. If containers are existed and existing localities can fully cover
the requested localities.
+ * For example if we have 5 containers on each node (host1: 5, host2: 5,
host3: 5, host4: 5),
+ * which could cover the current requested localities. This algorithm will
allocate all the
+ * requested containers with no localities.
+ */
+private[yarn] class LocalityPreferredContainerPlacementStrategy(
+ val sparkConf: SparkConf,
+ val yarnConf: Configuration,
+ val yarnAllocator: YarnAllocator) extends ContainerPlacementStrategy {
--- End diff --
Instead of passing in the whole yarnAllocator, can we pass in `resource`
and `allocatedHostToContainersMap` explicitly as arguments to the
`localityOfRequestedContainers` method so that it's clear what information is
used to make our decision?
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