TotalOrderPartitioner.java

package skywriting.examples.terasort;
/**
 * 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.
 */


import java.io.IOException;
import java.io.PrintStream;

import skywriting.examples.grep.Text;

/**
   * A partitioner that splits text keys into roughly equal partitions
   * in a global sorted order.
   */
  public class TotalOrderPartitioner {
    private TrieNode trie;
    private Text[] splitPoints;

    /**
     * A generic trie node
     */
    static abstract class TrieNode {
      private int level;
      TrieNode(int level) {
        this.level = level;
      }
      abstract int findPartition(Text key);
      abstract void print(PrintStream strm) throws IOException;
      int getLevel() {
        return level;
      }
    }

    /**
     * An inner trie node that contains 256 children based on the next
     * character.
     */
    static class InnerTrieNode extends TrieNode {
      private TrieNode[] child = new TrieNode[256];
      
      InnerTrieNode(int level) {
        super(level);
      }
      int findPartition(Text key) {
        int level = getLevel();
        if (key.getLength() <= level) {
          return child[0].findPartition(key);
        }
        return child[key.getBytes()[level]].findPartition(key);
      }
      void setChild(int idx, TrieNode child) {
        this.child[idx] = child;
      }
      void print(PrintStream strm) throws IOException {
        for(int ch=0; ch < 255; ++ch) {
          for(int i = 0; i < 2*getLevel(); ++i) {
            strm.print(' ');
          }
          strm.print(ch);
          strm.println(" ->");
          if (child[ch] != null) {
            child[ch].print(strm);
          }
        }
      }
    }

    /**
     * A leaf trie node that does string compares to figure out where the given
     * key belongs between lower..upper.
     */
    static class LeafTrieNode extends TrieNode {
      int lower;
      int upper;
      Text[] splitPoints;
      LeafTrieNode(int level, Text[] splitPoints, int lower, int upper) {
        super(level);
        this.splitPoints = splitPoints;
        this.lower = lower;
        this.upper = upper;
      }
      int findPartition(Text key) {
        for(int i=lower; i<upper; ++i) {
          if (splitPoints[i].compareTo(key) >= 0) {
            return i;
          }
        }
        return upper;
      }
      void print(PrintStream strm) throws IOException {
        for(int i = 0; i < 2*getLevel(); ++i) {
          strm.print(' ');
        }
        strm.print(lower);
        strm.print(", ");
        strm.println(upper);
      }
    }


    /**
     * Read the cut points from the given sequence file.
     * @param fs the file system
     * @param p the path to read
     * @param job the job config
     * @return the strings to split the partitions on
     * @throws IOException
     */
    /*private static Text[] readPartitions(FileSystem fs, Path p, 
                                         JobConf job) throws IOException {
      SequenceFile.Reader reader = new SequenceFile.Reader(fs, p, job);
      List<Text> parts = new ArrayList<Text>();
      Text key = new Text();
      NullWritable value = NullWritable.get();
      while (reader.next(key, value)) {
        parts.add(key);
        key = new Text();
      }
      reader.close();
      return parts.toArray(new Text[parts.size()]);  
    }*/

    /**
     * Given a sorted set of cut points, build a trie that will find the correct
     * partition quickly.
     * @param splits the list of cut points
     * @param lower the lower bound of partitions 0..numPartitions-1
     * @param upper the upper bound of partitions 0..numPartitions-1
     * @param prefix the prefix that we have already checked against
     * @param maxDepth the maximum depth we will build a trie for
     * @return the trie node that will divide the splits correctly
     */
    private static TrieNode buildTrie(Text[] splits, int lower, int upper, 
                                      Text prefix, int maxDepth) {
      int depth = prefix.getLength();
      if (depth >= maxDepth || lower == upper) {
        return new LeafTrieNode(depth, splits, lower, upper);
      }
      InnerTrieNode result = new InnerTrieNode(depth);
      Text trial = new Text(prefix);
      // append an extra byte on to the prefix
      trial.append(new byte[1], 0, 1);
      int currentBound = lower;
      for(int ch = 0; ch < 255; ++ch) {
        trial.getBytes()[depth] = (byte) (ch + 1);
        lower = currentBound;
        while (currentBound < upper) {
          if (splits[currentBound].compareTo(trial) >= 0) {
            break;
          }
          currentBound += 1;
        }
        trial.getBytes()[depth] = (byte) ch;
        result.child[ch] = buildTrie(splits, lower, currentBound, trial, 
                                     maxDepth);
      }
      // pick up the rest
      trial.getBytes()[depth] = 127;
      result.child[255] = buildTrie(splits, currentBound, upper, trial,
                                    maxDepth);
      return result;
    }

    public void configure(Text[] splitPoints) {
        /*FileSystem fs = FileSystem.getLocal(job);
        Path partFile = new Path(TeraInputFormat.PARTITION_FILENAME);
        splitPoints = readPartitions(fs, partFile, job);*/
        trie = buildTrie(splitPoints, 0, splitPoints.length, new Text(), 2);
        try {
        	trie.print(System.out);
        }
        catch(IOException e) {
        	System.out.println("Couldn't print trie: " + e);
        }
    }

    public TotalOrderPartitioner() {
    }

    public int getPartition(Text key, Text value, int numPartitions) {
      return trie.findPartition(key);
    }
    
  }