Java tutorial
/* * Copyright 2008-2013 LinkedIn, Inc * * Licensed 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 voldemort.routing; import java.util.ArrayList; import java.util.Collection; import java.util.HashSet; import java.util.List; import java.util.Set; import java.util.SortedMap; import java.util.TreeMap; import org.apache.log4j.Logger; import voldemort.cluster.Cluster; import voldemort.cluster.Node; import voldemort.utils.ByteUtils; import voldemort.utils.FnvHashFunction; import voldemort.utils.HashFunction; import com.google.common.collect.Sets; /** * A Routing strategy that routes each request to the first N nodes where N is a * user defined replication factor. * * The mapping is computed by creating partitions of a fixed size, and * maintaining a mapping from partition tag to Node. These nodes are mapped onto * a ring. * * A preference list of nodes to route to is created by taking the partition * into which the key hashes, and then taking the next N nodes on the ring. * * */ public class ConsistentRoutingStrategy implements RoutingStrategy { // the replication factor. private final int numReplicas; private final Node[] partitionToNode; private final HashFunction hash; private static final Logger logger = Logger.getLogger(ConsistentRoutingStrategy.class); public ConsistentRoutingStrategy(Cluster cluster, int numReplicas) { this(new FnvHashFunction(), cluster, numReplicas); } @Override public int getNumReplicas() { return this.numReplicas; } public Node[] getPartitionToNode() { return partitionToNode; } public ConsistentRoutingStrategy(HashFunction hash, Cluster cluster, int numReplicas) { this.numReplicas = numReplicas; this.hash = hash; this.partitionToNode = cluster.getPartitionIdToNodeArray(); } public ConsistentRoutingStrategy(HashFunction hash, Collection<Node> nodes, int numReplicas) { this.numReplicas = numReplicas; this.hash = hash; // sanity check that we dont assign the same partition to multiple nodes SortedMap<Integer, Node> m = new TreeMap<Integer, Node>(); for (Node n : nodes) { for (Integer partition : n.getPartitionIds()) { if (m.containsKey(partition)) throw new IllegalArgumentException( "Duplicate partition id " + partition + " in cluster configuration " + nodes); m.put(partition, n); } } this.partitionToNode = new Node[m.size()]; for (int i = 0; i < m.size(); i++) { if (!m.containsKey(i)) throw new IllegalArgumentException("Invalid configuration, missing partition " + i); this.partitionToNode[i] = m.get(i); } } /** * A modified version of abs that always returns a non-negative value. * Math.abs returns Integer.MIN_VALUE if a == Integer.MIN_VALUE and this * method returns Integer.MAX_VALUE in that case. */ private static int abs(int a) { if (a >= 0) return a; else if (a != Integer.MIN_VALUE) return -a; return Integer.MAX_VALUE; } @Override public List<Node> routeRequest(byte[] key) { List<Integer> partitionList = getPartitionList(key); if (partitionList.size() == 0) return new ArrayList<Node>(0); // pull out the nodes corresponding to the target partitions List<Node> preferenceList = new ArrayList<Node>(partitionList.size()); for (int partition : partitionList) { preferenceList.add(partitionToNode[partition]); } if (logger.isDebugEnabled()) { List<Integer> nodeIdList = new ArrayList<Integer>(); for (int partition : partitionList) { nodeIdList.add(partitionToNode[partition].getId()); } logger.debug("Key " + ByteUtils.toHexString(key) + " mapped to Nodes " + nodeIdList + " Partitions " + partitionList); } return preferenceList; } @Override public List<Integer> getReplicatingPartitionList(int index) { List<Node> preferenceList = new ArrayList<Node>(numReplicas); List<Integer> replicationPartitionsList = new ArrayList<Integer>(numReplicas); if (partitionToNode.length == 0) { return new ArrayList<Integer>(0); } // go over clockwise to find the next 'numReplicas' unique nodes // to replicate to for (int i = 0; i < partitionToNode.length; i++) { // add this one if we haven't already if (!preferenceList.contains(partitionToNode[index])) { preferenceList.add(partitionToNode[index]); replicationPartitionsList.add(index); } // if we have enough, go home if (preferenceList.size() >= numReplicas) return replicationPartitionsList; // move to next clockwise slot on the ring index = (index + 1) % partitionToNode.length; } // we don't have enough, but that may be okay return replicationPartitionsList; } /** * Obtain the master partition for a given key * * @param key * @return master partition id */ @Override public Integer getMasterPartition(byte[] key) { return abs(hash.hash(key)) % (Math.max(1, this.partitionToNode.length)); } @Override public Set<Node> getNodes() { Set<Node> s = Sets.newHashSetWithExpectedSize(partitionToNode.length); for (Node n : this.partitionToNode) s.add(n); return s; } Node getNodeByPartition(int partition) { return partitionToNode[partition]; } Set<Integer> getPartitionsByNode(Node n) { Set<Integer> tags = new HashSet<Integer>(); for (int i = 0; i < partitionToNode.length; i++) if (partitionToNode[i].equals(n)) tags.add(i); return tags; } @Override public List<Integer> getPartitionList(byte[] key) { // hash the key and perform a modulo on the total number of partitions, // to get the master partition int index = getMasterPartition(key); if (logger.isDebugEnabled()) { logger.debug("Key " + ByteUtils.toHexString(key) + " primary partition " + index); } // Now based on the preference list, pick the replicating partitions and // return return getReplicatingPartitionList(index); } @Override public String getType() { return RoutingStrategyType.CONSISTENT_STRATEGY; } }