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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
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/*
 * 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.cassandra.client;

import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.nio.ByteBuffer;
import java.util.List;

import org.apache.cassandra.dht.IPartitioner;
import org.apache.cassandra.dht.Range;
import org.apache.cassandra.dht.Token;
import org.apache.cassandra.hadoop.ConfigHelper;
import org.apache.cassandra.thrift.Cassandra;
import org.apache.cassandra.thrift.TokenRange;
import org.apache.hadoop.conf.Configuration;
import org.apache.thrift.TException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Multimap;

/**
 * A class for caching the ring map at the client. For usage example, see
 * test/unit/org.apache.cassandra.client.TestRingCache.java.
 * TODO: doing a naive linear search of the token map
 */
public class RingCache
{
    final private static Logger logger = LoggerFactory.getLogger(RingCache.class);

    private final IPartitioner partitioner;
    private final Configuration conf;

    private Multimap, InetAddress> rangeMap;

    public RingCache(Configuration conf)
    {
        this.conf = conf;
        this.partitioner = ConfigHelper.getOutputPartitioner(conf);
        refreshEndpointMap();
    }

    public void refreshEndpointMap()
    {
        try
        {
            Cassandra.Client client = ConfigHelper.getClientFromOutputAddressList(conf);

            String keyspace = ConfigHelper.getOutputKeyspace(conf);
            List ring = ConfigHelper.getOutputLocalDCOnly(conf)
                                  ? client.describe_local_ring(keyspace)
                                  : client.describe_ring(keyspace);
            rangeMap = ArrayListMultimap.create();

            for (TokenRange range : ring)
            {
                Token left = partitioner.getTokenFactory().fromString(range.start_token);
                Token right = partitioner.getTokenFactory().fromString(range.end_token);
                Range r = new Range(left, right);
                for (String host : range.endpoints)
                {
                    try
                    {
                        rangeMap.put(r, InetAddress.getByName(host));
                    } catch (UnknownHostException e)
                    {
                        throw new AssertionError(e); // host strings are IPs
                    }
                }
            }
        }
        catch (IOException e)
        {
            throw new RuntimeException(e);
        }
        catch (TException e)
        {
            logger.trace("Error contacting seed list {} {}", ConfigHelper.getOutputInitialAddress(conf), e.getMessage());
        }
    }

    /** ListMultimap promises to return a List for get(K) */
    public List getEndpoint(Range range)
    {
        return (List) rangeMap.get(range);
    }

    public List getEndpoint(ByteBuffer key)
    {
        return getEndpoint(getRange(key));
    }

    public Range getRange(ByteBuffer key)
    {
        // TODO: naive linear search of the token map
        Token t = partitioner.getToken(key);
        for (Range range : rangeMap.keySet())
            if (range.contains(t))
                return range;

        throw new RuntimeException("Invalid token information returned by describe_ring: " + rangeMap);
    }
}