[core] added configurable percentile values

In OneMeasurementHdrHistogram, now reading hdrhistogram.percentiles
from workload configuration. This property is a comma delimited string
of Integers to use as percentile values.

This implements #437

core/src/main/java/com/yahoo/ycsb/measurements/OneMeasurementHdrHistogram.java

@@ -23,8 +23,7 @@ import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.PrintStream;
 import java.text.DecimalFormat;
-import java.util.Map;
-import java.util.Properties;
+import java.util.*;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import org.HdrHistogram.Histogram;
@@ -49,8 +48,21 @@ public class OneMeasurementHdrHistogram extends OneMeasurement {
   final Recorder histogram;
   Histogram totalHistogram;
 
+  /**
+   * The name of the property for deciding what percentile values to output.
+   */
+  public static final String PERCENTILES_PROPERTY = "hdrhistogram.percentiles";
+
+  /**
+   * The default value for the hdrhistogram.percentiles property.
+   */
+  public static final String PERCENTILES_PROPERTY_DEFAULT = "95,99";
+
+  List<Integer> percentiles;
+
   public OneMeasurementHdrHistogram(String name, Properties props) {
     super(name);
+    percentiles = getPercentileValues(props.getProperty(PERCENTILES_PROPERTY, PERCENTILES_PROPERTY_DEFAULT));
     boolean shouldLog = Boolean.parseBoolean(props.getProperty("hdrhistogram.fileoutput", "false"));
     if (!shouldLog) {
       log = null;
@@ -101,8 +113,10 @@ public class OneMeasurementHdrHistogram extends OneMeasurement {
     exporter.write(getName(), "AverageLatency(us)", totalHistogram.getMean());
     exporter.write(getName(), "MinLatency(us)", totalHistogram.getMinValue());
     exporter.write(getName(), "MaxLatency(us)", totalHistogram.getMaxValue());
-    exporter.write(getName(), "95thPercentileLatency(us)", totalHistogram.getValueAtPercentile(90));
-    exporter.write(getName(), "99thPercentileLatency(us)", totalHistogram.getValueAtPercentile(99));
+
+    for (Integer percentile: percentiles) {
+      exporter.write(getName(), percentile + "thPercentileLatency(us)", totalHistogram.getValueAtPercentile(percentile));
+    }
     
     exportReturnCodes(exporter);
   }
@@ -142,4 +156,28 @@ public class OneMeasurementHdrHistogram extends OneMeasurement {
 		return intervalHistogram;
 	}
 
+  /**
+   * Helper method to parse the given percentile value string
+   *
+   * @param percentileString - comma delimited string of Integer values
+   * @return An Integer List of percentile values
+   */
+    private List<Integer> getPercentileValues(String percentileString) {
+      List<Integer> percentileValues = new ArrayList<Integer>();
+
+      try {
+        for (String rawPercentile: percentileString.split(",")) {
+          percentileValues.add(Integer.parseInt(rawPercentile));
+        }
+      } catch(Exception e) {
+        // If the given hdrhistogram.percentiles value is unreadable for whatever reason,
+        // then calculate and return the default set.
+        System.err.println("[WARN] Couldn't read " + PERCENTILES_PROPERTY + " value: '" + percentileString +
+            "', the default of '" + PERCENTILES_PROPERTY_DEFAULT + "' will be used.");
+        return getPercentileValues(PERCENTILES_PROPERTY_DEFAULT);
+      }
+
+      return percentileValues;
+    }
+
 }