HADOOP-11301. [optionally] update jmx cache to drop old metrics (Maysam Yabandeh via stack)

(cherry picked from commit b36f29298247f6c5db9f6eff7c2f5177a0fe3de5)
(cherry picked from commit 6d904985e8fbc5abbe9fe9f58badf5e0e1f55825)

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

@@ -20,6 +20,9 @@ Release 2.6.5 - UNRELEASED
     HADOOP-13298. Fix the leftover L&N files in
     hadoop-build-tools/src/main/resources/META-INF/. (ozawa)
 
+    HADOOP-11301. [optionally] update jmx cache to drop old metrics
+    (Maysam Yabandeh via stack)
+
   OPTIMIZATIONS
 
     HADOOP-12810. FileSystem#listLocatedStatus causes unnecessary RPC calls

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/impl/MetricsSourceAdapter.java

@@ -173,9 +173,8 @@ class MetricsSourceAdapter implements DynamicMBean {
     }
 
     synchronized(this) {
-      int oldCacheSize = attrCache.size();
-      int newCacheSize = updateAttrCache();
-      if (oldCacheSize < newCacheSize) {
+      updateAttrCache();
+      if (getAllMetrics) {
         updateInfoCache();
       }
       jmxCacheTS = Time.now();

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/impl/TestMetricsSourceAdapter.java

@@ -23,6 +23,8 @@ import static org.junit.Assert.*;
 import java.util.ArrayList;
 import java.util.List;
 
+import org.apache.hadoop.metrics2.MetricsCollector;
+import org.apache.hadoop.metrics2.MetricsRecordBuilder;
 import org.apache.hadoop.metrics2.MetricsSource;
 import org.apache.hadoop.metrics2.MetricsTag;
 import org.apache.hadoop.metrics2.annotation.Metric;
@@ -31,10 +33,59 @@ import org.apache.hadoop.metrics2.lib.MetricsAnnotations;
 import org.apache.hadoop.metrics2.lib.MetricsRegistry;
 import org.apache.hadoop.metrics2.lib.MetricsSourceBuilder;
 import org.apache.hadoop.metrics2.lib.MutableCounterLong;
+import static org.apache.hadoop.metrics2.lib.Interns.info;
+import static org.junit.Assert.assertEquals;
+
 import org.junit.Test;
 
+import javax.management.MBeanAttributeInfo;
+import javax.management.MBeanInfo;
+
 public class TestMetricsSourceAdapter {
 
+
+  @Test
+  public void testPurgeOldMetrics() throws Exception {
+    // create test source with a single metric counter of value 1
+    PurgableSource source = new PurgableSource();
+    MetricsSourceBuilder sb = MetricsAnnotations.newSourceBuilder(source);
+    final MetricsSource s = sb.build();
+
+    List<MetricsTag> injectedTags = new ArrayList<MetricsTag>();
+    MetricsSourceAdapter sa = new MetricsSourceAdapter(
+        "tst", "tst", "testdesc", s, injectedTags, null, null, 1, false);
+
+    MBeanInfo info = sa.getMBeanInfo();
+    boolean sawIt = false;
+    for (MBeanAttributeInfo mBeanAttributeInfo : info.getAttributes()) {
+      sawIt |= mBeanAttributeInfo.getName().equals(source.lastKeyName);
+    };
+    assertTrue("The last generated metric is not exported to jmx", sawIt);
+
+    Thread.sleep(1000); // skip JMX cache TTL
+
+    info = sa.getMBeanInfo();
+    sawIt = false;
+    for (MBeanAttributeInfo mBeanAttributeInfo : info.getAttributes()) {
+      sawIt |= mBeanAttributeInfo.getName().equals(source.lastKeyName);
+    };
+    assertTrue("The last generated metric is not exported to jmx", sawIt);
+  }
+
+  //generate a new key per each call
+  class PurgableSource implements MetricsSource {
+    int nextKey = 0;
+    String lastKeyName = null;
+    @Override
+    public void getMetrics(MetricsCollector collector, boolean all) {
+      MetricsRecordBuilder rb =
+          collector.addRecord("purgablesource")
+              .setContext("test");
+      lastKeyName = "key" + nextKey++;
+      rb.addGauge(info(lastKeyName, "desc"), 1);
+    }
+  }
+
   @Test
   public void testGetMetricsAndJmx() throws Exception {
     // create test source with a single metric counter of value 0