ReplicationMap.java

package com.splout.db.common;

/*
 * #%L
 * Splout SQL commons
 * %%
 * Copyright (C) 2012 Datasalt Systems S.L.
 * %%
 * 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.
 * #L%
 */

import org.codehaus.jackson.annotate.JsonIgnoreProperties;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * A Splout's replication map definition.
 * <p/>
 * A replication map is made up by a list of {@link ReplicationEntry}. Each of them specifies the list of addresses
 * (nodes) that hold the data for a shard. It is understood that if one {@link ReplicationEntry} has more than one node
 * then they will all hold the same data.
 */
@SuppressWarnings("serial")
@JsonIgnoreProperties(ignoreUnknown = true) // Backwards compatibility in JSON (new fields don't make things break)
public class ReplicationMap implements Serializable {

  public String toString() {
    return replicationEntries.toString();
  }

  List<ReplicationEntry> replicationEntries;

  public ReplicationMap() {
  }

  public ReplicationMap(List<ReplicationEntry> replicationMap) {
    this.replicationEntries = replicationMap;
  }

  public static ReplicationMap roundRobinMap(int nPartitions, int repFactor, String... hosts) {
    List<ReplicationEntry> repEntries = new ArrayList<ReplicationEntry>();
    for (int i = 0; i < nPartitions; i++) {
      int toNode = i % hosts.length;
      ReplicationEntry repEntry = new ReplicationEntry();
      repEntry.setShard(i);
      List<String> shardDNodes = new ArrayList<String>();
      for (int j = 0; j < repFactor; j++) {
        int chosen = (toNode + j) % hosts.length;
        shardDNodes.add(hosts[chosen]);
      }
      repEntry.setNodes(shardDNodes);
      repEntries.add(repEntry);
    }
    return new ReplicationMap(repEntries);
  }

  /**
   * Returns a one to one replication map with consecutive shard Ids from a list of hosts. This method is useful for
   * quickly having an instance of ReplicationMap that has no replication (1 shard -> 1 host).
   */
  public static ReplicationMap oneToOneMap(String... hosts) {
    List<ReplicationEntry> replicationMap = new ArrayList<ReplicationEntry>();
    int shard = 0;
    for (String host : hosts) {
      ReplicationEntry entry = new ReplicationEntry();
      entry.setNodes(Arrays.asList(new String[]{host}));
      entry.setShard(shard);
      replicationMap.add(entry);
      shard++;
    }
    return new ReplicationMap(replicationMap);
  }

  public List<ReplicationEntry> getReplicationEntries() {
    return replicationEntries;
  }

  public void setReplicationEntries(List<ReplicationEntry> replicationEntries) {
    this.replicationEntries = replicationEntries;
  }
}