code: /**
   * Copyright (c) 2010 Yahoo! Inc. All rights reserved.
   *
   * 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. See accompanying
   * LICENSE file.
   */
  
  package com.yahoo.ycsb.measurements;
  
  import java.io.IOException;
  import java.text.DecimalFormat;
  import java.util.Properties;
  
  import java.util.Map;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import com.yahoo.ycsb.measurements.exporter.MeasurementsExporter;
  
  
  /**
   * Take measurements and maintain a histogram of a given metric, such as READ LATENCY.
   *
   * @author cooperb
   *
   */
  public class OneMeasurementHistogram extends OneMeasurement
  {
    public static final String BUCKETS="histogram.buckets";
    public static final String BUCKETS_DEFAULT="1000";
  
  
    /**
     * Specify the range of latencies to track in the histogram.
     */
    int _buckets;
  
    /**
       * Groups operations in discrete blocks of 1ms width.
       */
    int[] histogram;
    
    /**
     * Counts all operations outside the histogram's range.
     */
    int histogramoverflow;
    
    /**
     * The total number of reported operations.
     */
    int operations;
    
    /**
     * The sum of each latency measurement over all operations.
     * Calculated in ms.
     */
    long totallatency;
  
    /**
     * The sum of each latency measurement squared over all operations. 
     * Used to calculate variance of latency.
     * Calculated in ms. 
     */
    double totalsquaredlatency;
    
    //keep a windowed version of these stats for printing status
    int windowoperations;
    long windowtotallatency;
  
    int min;
    int max;
  
    public OneMeasurementHistogram(String name, Properties props)
    {
      super(name);
      _buckets=Integer.parseInt(props.getProperty(BUCKETS, BUCKETS_DEFAULT));
      histogram=new int[_buckets];
      histogramoverflow=0;
      operations=0;
      totallatency=0;
      totalsquaredlatency=0;
      windowoperations=0;
      windowtotallatency=0;
      min=-1;
      max=-1;
    }
  
    /* (non-Javadoc)
     * @see com.yahoo.ycsb.OneMeasurement#measure(int)
     */
    public synchronized void measure(int latency)
    {
        //latency reported in us and collected in bucket by ms.
      if (latency/1000>=_buckets)
      {
        histogramoverflow++;
      }
      else
      {
        histogram[latency/1000]++;
      }
      operations++;
      totallatency += latency;
      totalsquaredlatency += ((double)latency) * ((double)latency);
      windowoperations++;
      windowtotallatency += latency;
  
      if ( (min<0) || (latency<min) )
      {
        min=latency;
      }
  
      if ( (max<0) || (latency>max) )
      {
        max=latency;
      }
    }
  
    @Override
    public void exportMeasurements(MeasurementsExporter exporter) throws IOException
    {
      double mean = totallatency/((double)operations);
      double variance = totalsquaredlatency/((double)operations) - (mean * mean);
      exporter.write(getName(), "Operations", operations);
      exporter.write(getName(), "AverageLatency(us)", mean);
      exporter.write(getName(), "LatencyVariance(us)", variance);
      exporter.write(getName(), "MinLatency(us)", min);
      exporter.write(getName(), "MaxLatency(us)", max);
  
      int opcounter=0;
      boolean done95th=false;
      for (int i=0; i<_buckets; i++)
      {
        opcounter+=histogram[i];
        if ( (!done95th) && (((double)opcounter)/((double)operations)>=0.95) )
        {
          exporter.write(getName(), "95thPercentileLatency(us)", i*1000);
          done95th=true;
        }
        if (((double)opcounter)/((double)operations)>=0.99)
        {
          exporter.write(getName(), "99thPercentileLatency(us)", i*1000);
          break;
        }
      }
  
      exportStatusCounts(exporter);
  
      for (int i=0; i<_buckets; i++)
      {
        exporter.write(getName(), Integer.toString(i), histogram[i]);
      }
      exporter.write(getName(), ">"+_buckets, histogramoverflow);
    }
  
    @Override
    public String getSummary() {
      if (windowoperations==0)
      {
        return "";
      }
      DecimalFormat d = new DecimalFormat("#.##");
      double report=((double)windowtotallatency)/((double)windowoperations);
      windowtotallatency=0;
      windowoperations=0;
      return "["+getName()+" AverageLatency(us)="+d.format(report)+"]";
    }
  }
  