HADOOP-8929. Add toString, other improvements for SampleQuantiles. Contributed by Todd Lipcon.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1398658 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -318,6 +318,8 @@ Release 2.0.3-alpha - Unreleased
 
     HADOOP-8784. Improve IPC.Client's token use (daryn)
 
+    HADOOP-8929. Add toString, other improvements for SampleQuantiles (todd)
+
   OPTIMIZATIONS
 
     HADOOP-8866. SampleQuantiles#query is O(N^2) instead of O(N). (Andrew Wang

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/lib/MutableQuantiles.java

@@ -20,7 +20,6 @@ package org.apache.hadoop.metrics2.lib;
 
 import static org.apache.hadoop.metrics2.lib.Interns.info;
 
-import java.io.IOException;
 import java.util.Map;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
@@ -150,14 +149,8 @@ public class MutableQuantiles extends MutableMetric {
     @Override
     public void run() {
       synchronized (parent) {
-        try {
-          parent.previousCount = parent.estimator.getCount();
-          parent.previousSnapshot = parent.estimator.snapshot();
-        } catch (IOException e) {
-          // Couldn't get a new snapshot because the window was empty
-          parent.previousCount = 0;
-          parent.previousSnapshot = null;
-        }
+        parent.previousCount = parent.estimator.getCount();
+        parent.previousSnapshot = parent.estimator.snapshot();
         parent.estimator.clear();
       }
       parent.setChanged();

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/util/Quantile.java

@@ -20,12 +20,14 @@ package org.apache.hadoop.metrics2.util;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 
+import com.google.common.collect.ComparisonChain;
+
 /**
  * Specifies a quantile (with error bounds) to be watched by a
  * {@link SampleQuantiles} object.
  */
 @InterfaceAudience.Private
-public class Quantile {
+public class Quantile implements Comparable<Quantile> {
   public final double quantile;
   public final double error;
 
@@ -57,4 +59,19 @@ public class Quantile {
     return (int) (Double.doubleToLongBits(quantile) ^ Double
         .doubleToLongBits(error));
   }
+
+  @Override
+  public int compareTo(Quantile other) {
+    return ComparisonChain.start()
+        .compare(quantile, other.quantile)
+        .compare(error, other.error)
+        .result();
+  }
+  
+  @Override
+  public String toString() {
+    return String.format("%.2f %%ile +/- %.2f%%",
+        quantile * 100, error * 100);
+  }
+
 }

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/util/SampleQuantiles.java

@@ -18,16 +18,17 @@
 
 package org.apache.hadoop.metrics2.util;
 
-import java.io.IOException;
 import java.util.Arrays;
-import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.ListIterator;
 import java.util.Map;
+import java.util.TreeMap;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Joiner;
+import com.google.common.base.Preconditions;
 
 /**
  * Implementation of the Cormode, Korn, Muthukrishnan, and Srivastava algorithm
@@ -202,10 +203,8 @@ public class SampleQuantiles {
    * @param quantile Queried quantile, e.g. 0.50 or 0.99.
    * @return Estimated value at that quantile.
    */
-  private long query(double quantile) throws IOException {
-    if (samples.size() == 0) {
-      throw new IOException("No samples present");
-    }
+  private long query(double quantile) {
+    Preconditions.checkState(!samples.isEmpty(), "no data in estimator");
 
     int rankMin = 0;
     int desired = (int) (quantile * count);
@@ -231,14 +230,18 @@ public class SampleQuantiles {
   /**
    * Get a snapshot of the current values of all the tracked quantiles.
    * 
-   * @return snapshot of the tracked quantiles
-   * @throws IOException
-   *           if no items have been added to the estimator
+   * @return snapshot of the tracked quantiles. If no items are added
+   * to the estimator, returns null.
    */
-  synchronized public Map<Quantile, Long> snapshot() throws IOException {
+  synchronized public Map<Quantile, Long> snapshot() {
     // flush the buffer first for best results
     insertBatch();
-    Map<Quantile, Long> values = new HashMap<Quantile, Long>(quantiles.length);
+    
+    if (samples.isEmpty()) {
+      return null;
+    }
+    
+    Map<Quantile, Long> values = new TreeMap<Quantile, Long>();
     for (int i = 0; i < quantiles.length; i++) {
       values.put(quantiles[i], query(quantiles[i].quantile));
     }
@@ -273,6 +276,16 @@ public class SampleQuantiles {
     bufferCount = 0;
     samples.clear();
   }
+  
+  @Override
+  synchronized public String toString() {
+    Map<Quantile, Long> data = snapshot();
+    if (data == null) {
+      return "[no samples]";
+    } else {
+      return Joiner.on("\n").withKeyValueSeparator(": ").join(data);
+    }
+  }
 
   /**
    * Describes a measured value passed to the estimator, tracking additional

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/util/TestSampleQuantiles.java

@@ -18,9 +18,7 @@
 
 package org.apache.hadoop.metrics2.util;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.fail;
+import static org.junit.Assert.*;
 
 import java.io.IOException;
 import java.util.Arrays;
@@ -28,7 +26,6 @@ import java.util.Collections;
 import java.util.Map;
 import java.util.Random;
 
-import org.apache.hadoop.test.GenericTestUtils;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -54,18 +51,22 @@ public class TestSampleQuantiles {
     // Counts start off zero
     assertEquals(estimator.getCount(), 0);
     assertEquals(estimator.getSampleCount(), 0);
-    try {
-      estimator.snapshot();
-      fail("Expected IOException from empty window");
-    } catch (IOException e) {
-      GenericTestUtils.assertExceptionContains("No samples", e);
-    }
+    
+    // Snapshot should be null if there are no entries.
+    assertNull(estimator.snapshot());
 
     // Count increment correctly by 1
     estimator.insert(1337);
     assertEquals(estimator.getCount(), 1);
     estimator.snapshot();
     assertEquals(estimator.getSampleCount(), 1);
+    
+    assertEquals(
+        "50.00 %ile +/- 5.00%: 1337\n" +
+        "75.00 %ile +/- 2.50%: 1337\n" +
+        "90.00 %ile +/- 1.00%: 1337\n" +
+        "95.00 %ile +/- 0.50%: 1337\n" +
+        "99.00 %ile +/- 0.10%: 1337", estimator.toString());
   }
 
   /**
@@ -80,12 +81,7 @@ public class TestSampleQuantiles {
     estimator.clear();
     assertEquals(estimator.getCount(), 0);
     assertEquals(estimator.getSampleCount(), 0);
-    try {
-      estimator.snapshot();
-      fail("Expected IOException for an empty window.");
-    } catch (IOException e) {
-      GenericTestUtils.assertExceptionContains("No samples", e);
-    }
+    assertNull(estimator.snapshot());
   }
 
   /**