/*

  * 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.giraph.graph.partition;

 import java.util.ArrayList;

 import java.util.Collection;

 import java.util.Iterator;

 import java.util.List;

 import org.apache.giraph.graph.WorkerInfo;

 import org.apache.hadoop.conf.Configuration;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.io.WritableComparable;

 import org.apache.log4j.Logger;

 /**

  * Master will execute a hash based partitioning.

  *

  * @param <I> Vertex index value

  * @param <V> Vertex value

  * @param <E> Edge value

  * @param <M> Message value

  */

 @SuppressWarnings("rawtypes")

 public class HashMasterPartitioner<I extends WritableComparable,

     V extends Writable, E extends Writable, M extends Writable> implements

     MasterGraphPartitioner<I, V, E, M> {

   /** Multiplier for the current workers squared */

   public static final String PARTITION_COUNT_MULTIPLIER =

     "hash.masterPartitionCountMultipler";

   /** Default mulitplier for current workers squared */

   public static final float DEFAULT_PARTITION_COUNT_MULTIPLIER = 1.0f;

   /** Overrides default partition count calculation if not -1 */

   public static final String USER_PARTITION_COUNT =

     "hash.userPartitionCount";

   /** Default user partition count */

   public static final int DEFAULT_USER_PARTITION_COUNT = -1;

   /** Class logger */

   private static Logger LOG = Logger.getLogger(HashMasterPartitioner.class);

   /**

    * ZooKeeper has a limit of the data in a single znode of 1 MB and

    * each entry can go be on the average somewhat more than 300 bytes

    */

   private static final int MAX_PARTTIONS = 1024 * 1024 / 350;

   /** Provided configuration */

   private Configuration conf;

   /** Specified partition count (overrides calculation) */

   private final int userPartitionCount;

   /** Partition count (calculated in createInitialPartitionOwners) */

   private int partitionCount = -1;

   /** Save the last generated partition owner list */

   private List<PartitionOwner> partitionOwnerList;

   /**

    * Constructor.

    *

    *@param conf Configuration used.

    */

   public HashMasterPartitioner(Configuration conf) {

     this.conf = conf;

     userPartitionCount = conf.getInt(USER_PARTITION_COUNT,

         DEFAULT_USER_PARTITION_COUNT);

   }

   @Override

   public Collection<PartitionOwner> createInitialPartitionOwners(

       Collection<WorkerInfo> availableWorkerInfos, int maxWorkers) {

     if (availableWorkerInfos.isEmpty()) {

       throw new IllegalArgumentException(

           "createInitialPartitionOwners: No available workers");

     }

     List<PartitionOwner> ownerList = new ArrayList<PartitionOwner>();

     Iterator<WorkerInfo> workerIt = availableWorkerInfos.iterator();

     if (userPartitionCount == DEFAULT_USER_PARTITION_COUNT) {

       float multiplier = conf.getFloat(

           PARTITION_COUNT_MULTIPLIER,

           DEFAULT_PARTITION_COUNT_MULTIPLIER);

       partitionCount =

           Math.max((int) (multiplier * availableWorkerInfos.size() *

               availableWorkerInfos.size()),

               1);

     } else {

       partitionCount = userPartitionCount;

     }

     if (LOG.isInfoEnabled()) {

       LOG.info("createInitialPartitionOwners: Creating " +

         partitionCount + ", default would have been " +

         (availableWorkerInfos.size() *

          availableWorkerInfos.size()) + " partitions.");

     }

     if (partitionCount > MAX_PARTTIONS) {

       LOG.warn("createInitialPartitionOwners: " +

           "Reducing the partitionCount to " + MAX_PARTTIONS +

           " from " + partitionCount);

       partitionCount = MAX_PARTTIONS;

     }

     for (int i = 0; i < partitionCount; ++i) {

       PartitionOwner owner = new BasicPartitionOwner(i, workerIt.next());

       if (!workerIt.hasNext()) {

         workerIt = availableWorkerInfos.iterator();

       }

       ownerList.add(owner);

     }

     this.partitionOwnerList = ownerList;

     return ownerList;

   }

   @Override

   public Collection<PartitionOwner> getCurrentPartitionOwners() {

     return partitionOwnerList;

   }

   /**

    * Subclasses can set the partition owner list.

    *

    * @param partitionOwnerList New partition owner list.

    */

   protected void setPartitionOwnerList(List<PartitionOwner>

   partitionOwnerList) {

     this.partitionOwnerList = partitionOwnerList;

   }

   @Override

   public Collection<PartitionOwner> generateChangedPartitionOwners(

       Collection<PartitionStats> allPartitionStatsList,

       Collection<WorkerInfo> availableWorkerInfos,

       int maxWorkers,

       long superstep) {

     return PartitionBalancer.balancePartitionsAcrossWorkers(

         conf,

         partitionOwnerList,

         allPartitionStatsList,

         availableWorkerInfos);

   }

   @Override

   public PartitionStats createPartitionStats() {

     return new PartitionStats();

   }

 }