HBASE-24615 MutableRangeHistogram#updateSnapshotRangeMetrics doesn't calculate the distribution for last bucket

Closes #1962

Signed-off-by: David Manning
Signed-off-by: Rushabh
Signed-off-by: Viraj Jasani <vjasani@apache.org>

hbase-hadoop-compat/src/main/java/org/apache/hadoop/metrics2/lib/MutableRangeHistogram.java

@@ -67,7 +67,7 @@ public abstract class MutableRangeHistogram extends MutableHistogram implements
 
     final long[] ranges = getRanges();
     final String rangeType = getRangeType();
-    for (int i = 0; i < ranges.length - 1; i++) {
+    for (int i = 0; i < ranges.length; i++) {
       long val = snapshot.getCountAtOrBelow(ranges[i]);
       if (val - cumNum > 0) {
         metricsRecordBuilder.addCounter(
@@ -80,7 +80,7 @@ public abstract class MutableRangeHistogram extends MutableHistogram implements
     long val = snapshot.getCount();
     if (val - cumNum > 0) {
       metricsRecordBuilder.addCounter(
-          Interns.info(name + "_" + rangeType + "_" + ranges[ranges.length - 1] + "-inf", desc),
+          Interns.info(name + "_" + rangeType + "_" + priorRange + "-inf", desc),
           val - cumNum);
     }
   }

hbase-hadoop-compat/src/test/java/org/apache/hadoop/metrics2/lib/TestMutableRangeHistogram.java

@@ -0,0 +1,90 @@
+/**
+ * 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.
+ */
+
+package org.apache.hadoop.metrics2.lib;
+
+import static org.junit.Assert.assertEquals;
+
+import org.apache.hadoop.hbase.HBaseClassTestRule;
+import org.apache.hadoop.hbase.testclassification.MetricsTests;
+import org.apache.hadoop.hbase.testclassification.SmallTests;
+import org.apache.hadoop.metrics2.AbstractMetric;
+import org.apache.hadoop.metrics2.MetricsRecord;
+import org.apache.hadoop.metrics2.impl.MetricsCollectorImpl;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+import java.util.ArrayList;
+import java.util.List;
+
+@Category({ MetricsTests.class, SmallTests.class })
+public class TestMutableRangeHistogram {
+
+  @ClassRule
+  public static final HBaseClassTestRule CLASS_RULE =
+    HBaseClassTestRule.forClass(TestMutableRangeHistogram.class);
+
+  private static final String RECORD_NAME = "test";
+  private static final String SIZE_HISTOGRAM_NAME = "TestSize";
+
+  /**
+   * calculate the distribution for last bucket, see HBASE-24615 for detail.
+   */
+  @Test
+  public void testLastBucketWithSizeHistogram() {
+    // create and init histogram minValue and maxValue
+    MetricsCollectorImpl collector = new MetricsCollectorImpl();
+    MutableSizeHistogram histogram = new MutableSizeHistogram(SIZE_HISTOGRAM_NAME, "");
+    long[] ranges = histogram.getRanges();
+    int len = ranges.length;
+    histogram.add(0L);
+    histogram.add(ranges[len - 1]);
+    histogram.snapshot(collector.addRecord(RECORD_NAME), true);
+    collector.clear();
+
+    // fill up values and snapshot
+    histogram.add(ranges[len - 2] * 2);
+    histogram.add(ranges[len - 1] * 2);
+    histogram.snapshot(collector.addRecord(RECORD_NAME), true);
+    List<? extends MetricsRecord> records = collector.getRecords();
+    assertEquals(1, records.size());
+    MetricsRecord record = records.iterator().next();
+    assertEquals(RECORD_NAME, record.name());
+
+    // get size range metrics
+    String histogramMetricPrefix = SIZE_HISTOGRAM_NAME + "_" + histogram.getRangeType();
+    List<AbstractMetric> metrics = new ArrayList<>();
+    for (AbstractMetric metric : record.metrics()) {
+      if (metric.name().startsWith(histogramMetricPrefix)) {
+        metrics.add(metric);
+      }
+    }
+    assertEquals(2, metrics.size());
+
+    // check range [10000000,100000000]
+    String metricName = histogramMetricPrefix + "_" + ranges[len - 2] + "-" + ranges[len - 1];
+    assertEquals(metricName, metrics.get(0).name());
+    assertEquals(1, metrics.get(0).value().longValue());
+
+    // check range [100000000, inf]
+    metricName = histogramMetricPrefix + "_" + ranges[len - 1] + "-inf";
+    assertEquals(metricName, metrics.get(1).name(), metricName);
+    assertEquals(1, metrics.get(1).value().longValue());
+  }
+}