edu.yale.cs.hadoopdb.connector.DBChunk.java Source code

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Here is the source code for edu.yale.cs.hadoopdb.connector.DBChunk.java

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/**
 * Copyright 2009 HadoopDB Team (http://db.cs.yale.edu/hadoopdb/hadoopdb.html)
 *
 * 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 edu.yale.cs.hadoopdb.connector;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Random;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * For each relation chunk, this object stores connection and location
 * information in a collection of DBChunkHost identified by their location or
 * host address. This class and all included classes are serialized by
 * DBInputSplit
 */
public class DBChunk implements Serializable {

    private static final long serialVersionUID = 2154832951481581295L;
    private static Random R = new Random(System.currentTimeMillis());

    private String id;
    private HashMap<String, DBChunkHost> locations = new HashMap<String, DBChunkHost>();

    public static final Log LOG = LogFactory.getLog(DBChunk.class.getName());

    public DBChunk(String id) {
        this.id = id;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public void addHost(DBChunkHost host) {
        locations.put(host.getHost(), host);
    }

    public DBChunkHost getHost(String host) {
        return locations.get(host);
    }

    /**
     * Randomly chooses a host from the set of hosts containing the chunk.
     */
    public DBChunkHost getAnyHost() {
        int size = locations.keySet().size();
        int skip = R.nextInt(size);

        Iterator<String> it = locations.keySet().iterator();
        for (int i = 0; i < skip; i++) {
            it.next();
        }

        String host = it.next();

        return getHost(host);
    }

    /**
     * Randomly chooses a host from the set of hosts avoiding if possible the
     * given host
     */
    public DBChunkHost getAnyHost(DBChunkHost avoid_host) {

        if (avoid_host == null) {
            return getAnyHost();
        }

        List<DBChunkHost> nds = new ArrayList<DBChunkHost>();
        nds.addAll(this.locations.values());
        nds.remove(avoid_host);

        if (nds.size() == 0) {
            LOG.warn("Request to avoid host " + avoid_host + " unsatisfiable -" + "- only one host for chunk "
                    + this.getId());
            return getAnyHost();
        }
        return nds.get(R.nextInt(nds.size()));
    }

    public Collection<DBChunkHost> getHosts() {
        return locations.values();
    }

    public Collection<String> getLocations() {
        return locations.keySet();
    }

    public String toString() {
        return this.id;
    }

}