Github user HyukjinKwon commented on a diff in the pull request:
https://github.com/apache/spark/pull/13152#discussion_r63636294
--- Diff:
core/src/main/scala/org/apache/spark/storage/BlockReplicationPrioritization.scala
---
@@ -0,0 +1,72 @@
+/*
+ * 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.storage
+
+import org.apache.spark.annotation.DeveloperApi
+
+import scala.util.Random
+import org.apache.spark.internal.Logging
+
+/**
+ * ::DeveloperApi::
+ * BlockReplicationPrioritization provides logic for prioritizing a
sequence of peers for
+ * replicating blocks
+ */
+@DeveloperApi
+trait BlockReplicationPrioritization {
+
+ /**
+ * Method to prioritize a bunch of candidate peers of a block
+ *
+ * @param peers A list of peers of a BlockManager
+ * @param peersReplicatedTo Set of peers already replicated to
+ * @param blockId BlockId of the block being replicated. This can be
used as a source of
+ * randomness if needed.
+ * @return A prioritized list of peers. Lower the index of a peer,
higher its priority
+ */
+ def prioritize(peers: Seq[BlockManagerId],
+ peersReplicatedTo: Set[BlockManagerId],
+ blockId: BlockId): Seq[BlockManagerId]
+}
+
+@DeveloperApi
+class DefaultBlockReplicationPrioritization(host: String)
+ extends BlockReplicationPrioritization
+ with Logging {
+
+ /**
+ * Method to prioritize a bunch of candidate peers of a block. This is a
basic implementation,
+ * that just makes sure we put blocks on different hosts, if possible
+ *
+ * @param peers A list of peers of a BlockManager
+ * @param peersReplicatedTo Set of peers already replicated to
+ * @param blockId BlockId of the block being replicated. This can be
used as a source of
+ * randomness if needed.
+ * @return A prioritized list of peers. Lower the index of a peer,
higher its priority
+ */
+ override def prioritize(peers: Seq[BlockManagerId],
+ peersReplicatedTo: Set[BlockManagerId],
+ blockId: BlockId): Seq[BlockManagerId] = {
--- End diff --
Here too..
```scala
override def prioritize(peers: Seq[BlockManagerId],
peersReplicatedTo: Set[BlockManagerId],
blockId: BlockId): Seq[BlockManagerId] = {
```
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