Java tutorial
/* * 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.mapping; import org.apache.hadoop.io.ByteWritable; import org.apache.hadoop.io.LongWritable; /** * Implementation of basic methods in MappingStoreOps */ @SuppressWarnings("unchecked, rawtypes") public abstract class AbstractLongByteOps implements MappingStoreOps<LongWritable, ByteWritable> { /** Mapping store instance to operate on */ protected LongByteMappingStore mappingStore; @Override public void initialize(MappingStore<LongWritable, ByteWritable> mappingStore) { this.mappingStore = (LongByteMappingStore) mappingStore; } /** * Compute partition given id, partitionCount, workerCount & target * @param id vertex id * @param partitionCount number of partitions * @param workerCount number of workers * @param target target worker * @return partition number */ protected int computePartition(LongWritable id, int partitionCount, int workerCount, byte target) { int numRows = partitionCount / workerCount; numRows = (numRows * workerCount == partitionCount) ? numRows : numRows + 1; if (target == -1) { // default to hash based partitioning return Math.abs(id.hashCode() % partitionCount); } else { int targetWorker = target & 0xFF; // assume zero based indexing of partition & worker [also consecutive] return numRows * targetWorker + Math.abs(id.hashCode() % numRows); } } }