/**
 * 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.
 */
//NOTE: This code is taken almost verbatim from HBase 0.95. As versions increase
//this class may become unnecessary and undesirable
package com.splicemachine.hbase.balancer;

import org.apache.hadoop.hbase.ServerName;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.ClusterStatus;
import org.apache.hadoop.hbase.HDFSBlocksDistribution;
import org.apache.hadoop.hbase.HRegionInfo;
import org.apache.hadoop.hbase.HTableDescriptor;
import org.apache.hadoop.hbase.ServerName;
import org.apache.hadoop.hbase.master.MasterServices;
import org.apache.hadoop.hbase.regionserver.HRegion;
import org.apache.hadoop.hbase.util.Bytes;

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;

/**
 * This will find where data for a region is located in HDFS. It ranks
 * {@link ServerName}'s by the size of the store files they are holding for a
 * given region.
 *
 */
class RegionLocationFinder {

    private static Log LOG = LogFactory.getLog(RegionLocationFinder.class);

    private Configuration conf;
    private ClusterStatus status;
    private MasterServices services;

    private CacheLoader<HRegionInfo, List<ServerName>> loader =
            new CacheLoader<HRegionInfo, List<ServerName>>() {

                @Override
                public List<ServerName> load(HRegionInfo key) throws Exception {
                    List<ServerName> servers = internalGetTopBlockLocation(key);
                    if (servers == null) {
                        return new LinkedList<ServerName>();
                    }
                    return servers;
                }
            };

    // The cache for where regions are located.
    private LoadingCache<HRegionInfo, List<ServerName>> cache = null;

    /**
     * Create a cache for region to list of servers
     * @param mins Number of mins to cache
     * @return A new Cache.
     */
    private LoadingCache<HRegionInfo, List<ServerName>> createCache(int mins) {
        return CacheBuilder.newBuilder().expireAfterAccess(mins, TimeUnit.MINUTES).build(loader);
    }

    public Configuration getConf() {
        return conf;
    }

    public void setConf(Configuration conf) {
        this.conf = conf;
        cache = createCache(conf.getInt("hbase.master.balancer.regionLocationCacheTime", 30));
    }

    public void setServices(MasterServices services) {
        this.services = services;
    }

    public void setClusterStatus(ClusterStatus status) {
        this.status = status;
    }

    protected List<ServerName> getTopBlockLocations(HRegionInfo region) {
        List<ServerName> servers = null;
        try {
            servers = cache.get(region);
        } catch (ExecutionException ex) {
            servers = new LinkedList<ServerName>();
        }
        return servers;

    }

    /**
     * Returns an ordered list of hosts that are hosting the blocks for this
     * region. The weight of each host is the sum of the block lengths of all
     * files on that host, so the first host in the list is the server which holds
     * the most bytes of the given region's HFiles.
     *
     * @param region region
     * @return ordered list of hosts holding blocks of the specified region
     */
    protected List<ServerName> internalGetTopBlockLocation(HRegionInfo region) {
        List<ServerName> topServerNames = null;
        try {
            HTableDescriptor tableDescriptor = getTableDescriptor(region.getTableName());
            if (tableDescriptor != null) {
                HDFSBlocksDistribution blocksDistribution =
                        HRegion.computeHDFSBlocksDistribution(getConf(), tableDescriptor, region.getEncodedName());
                List<String> topHosts = blocksDistribution.getTopHosts();
                topServerNames = mapHostNameToServerName(topHosts);
            }
        } catch (IOException ioe) {
            LOG.debug("IOException during HDFSBlocksDistribution computation. for " + "region = "
                    + region.getEncodedName(), ioe);
        }

        return topServerNames;
    }

    /**
     * return HTableDescriptor for a given tableName
     *
     * @param tableName the table name
     * @return HTableDescriptor
     * @throws IOException
     */
    protected HTableDescriptor getTableDescriptor(byte[] tableName) throws IOException {
        HTableDescriptor tableDescriptor = null;
        try {
            if (this.services != null) {
                tableDescriptor = this.services.getTableDescriptors().get(Bytes.toString(tableName));
            }
        } catch (FileNotFoundException fnfe) {
            LOG.debug("FileNotFoundException during getTableDescriptors." + " Current table name = "
                    + Bytes.toStringBinary(tableName), fnfe);
        }

        return tableDescriptor;
    }

    /**
     * Map hostname to ServerName, The output ServerName list will have the same
     * order as input hosts.
     *
     * @param hosts the list of hosts
     * @return ServerName list
     */
    protected List<ServerName> mapHostNameToServerName(List<String> hosts) {
        if (hosts == null || status == null) {
            return null;
        }

        List<ServerName> topServerNames = new ArrayList<ServerName>();
        Collection<ServerName> regionServers = status.getServers();

        // create a mapping from hostname to ServerName for fast lookup
        HashMap<String, ServerName> hostToServerName = new HashMap<String, ServerName>();
        for (ServerName sn : regionServers) {
            hostToServerName.put(sn.getHostname(), sn);
        }

        for (String host : hosts) {
            ServerName sn = hostToServerName.get(host);
            // it is possible that HDFS is up ( thus host is valid ),
            // but RS is down ( thus sn is null )
            if (sn != null) {
                topServerNames.add(sn);
            }
        }
        return topServerNames;
    }
}

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@@ -3741,32 +3741,29 @@
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