HADOOP-14960. Add GC time percentage monitor/alerter. Contributed by Misha Dmitriev.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/source/JvmMetrics.java

@@ -28,6 +28,8 @@ import java.util.List;
 import java.util.concurrent.ConcurrentHashMap;
 
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
+
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.log.metrics.EventCounter;
 import org.apache.hadoop.metrics2.MetricsCollector;
@@ -39,6 +41,8 @@ import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
 import org.apache.hadoop.metrics2.lib.Interns;
 import static org.apache.hadoop.metrics2.source.JvmMetricsInfo.*;
 import static org.apache.hadoop.metrics2.impl.MsInfo.*;
+
+import org.apache.hadoop.util.GcTimeMonitor;
 import org.apache.hadoop.util.JvmPauseMonitor;
 
 /**
@@ -85,6 +89,7 @@ public class JvmMetrics implements MetricsSource {
   private JvmPauseMonitor pauseMonitor = null;
   final ConcurrentHashMap<String, MetricsInfo[]> gcInfoCache =
       new ConcurrentHashMap<String, MetricsInfo[]>();
+  private GcTimeMonitor gcTimeMonitor = null;
 
   @VisibleForTesting
   JvmMetrics(String processName, String sessionId) {
@@ -96,6 +101,11 @@ public class JvmMetrics implements MetricsSource {
     this.pauseMonitor = pauseMonitor;
   }
 
+  public void setGcTimeMonitor(GcTimeMonitor gcTimeMonitor) {
+    Preconditions.checkNotNull(gcTimeMonitor);
+    this.gcTimeMonitor = gcTimeMonitor;
+  }
+
   public static JvmMetrics create(String processName, String sessionId,
                                   MetricsSystem ms) {
     return ms.register(JvmMetrics.name(), JvmMetrics.description(),
@@ -176,6 +186,11 @@ public class JvmMetrics implements MetricsSource {
       rb.addCounter(GcTotalExtraSleepTime,
           pauseMonitor.getTotalGcExtraSleepTime());
     }
+
+    if (gcTimeMonitor != null) {
+      rb.addCounter(GcTimePercentage,
+          gcTimeMonitor.getLatestGcData().getGcTimePercentage());
+    }
   }
 
   private MetricsInfo[] getGcInfo(String gcName) {

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/source/JvmMetricsInfo.java

@@ -51,7 +51,8 @@ public enum JvmMetricsInfo implements MetricsInfo {
   LogInfo("Total number of info log events"),
   GcNumWarnThresholdExceeded("Number of times that the GC warn threshold is exceeded"),
   GcNumInfoThresholdExceeded("Number of times that the GC info threshold is exceeded"),
-  GcTotalExtraSleepTime("Total GC extra sleep time in milliseconds");
+  GcTotalExtraSleepTime("Total GC extra sleep time in milliseconds"),
+  GcTimePercentage("Percentage of time the JVM was paused in GC");
 
   private final String desc;
 

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

@@ -0,0 +1,242 @@
+/**
+ * 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.util;
+
+import com.google.common.base.Preconditions;
+
+import java.lang.management.GarbageCollectorMXBean;
+import java.lang.management.ManagementFactory;
+import java.util.List;
+
+/**
+ * This class monitors the percentage of time the JVM is paused in GC within
+ * the specified observation window, say 1 minute. The user can provide a
+ * hook which will be called whenever this percentage exceeds the specified
+ * threshold.
+ */
+public class GcTimeMonitor extends Thread {
+
+  private final long maxGcTimePercentage;
+  private final long observationWindowMs, sleepIntervalMs;
+  private final GcTimeAlertHandler alertHandler;
+
+  private final List<GarbageCollectorMXBean> gcBeans =
+      ManagementFactory.getGarbageCollectorMXBeans();
+  // Ring buffers containing GC timings and timestamps when timings were taken
+  private final TsAndData[] gcDataBuf;
+  private int bufSize, startIdx, endIdx;
+
+  private long startTime;
+  private final GcData curData = new GcData();
+  private volatile boolean shouldRun = true;
+
+  /**
+   * Create an instance of GCTimeMonitor. Once it's started, it will stay alive
+   * and monitor GC time percentage until shutdown() is called. If you don't
+   * put a limit on the number of GCTimeMonitor instances that you create, and
+   * alertHandler != null, you should necessarily call shutdown() once the given
+   * instance is not needed. Otherwise, you may create a memory leak, because
+   * each running GCTimeMonitor will keep its alertHandler object in memory,
+   * which in turn may reference and keep in memory many more other objects.
+   *
+   * @param observationWindowMs the interval over which the percentage
+   *   of GC time should be calculated. A practical value would be somewhere
+   *   between 30 sec and several minutes.
+   * @param sleepIntervalMs how frequently this thread should wake up to check
+   *   GC timings. This is also a frequency with which alertHandler will be
+   *   invoked if GC time percentage exceeds the specified limit. A practical
+   *   value would likely be 500..1000 ms.
+   * @param maxGcTimePercentage A GC time percentage limit (0..100) within
+   *   observationWindowMs. Once this is exceeded, alertHandler will be
+   *   invoked every sleepIntervalMs milliseconds until GC time percentage
+   *   falls below this limit.
+   * @param alertHandler a single method in this interface is invoked when GC
+   *   time percentage exceeds the specified limit.
+   */
+  public GcTimeMonitor(long observationWindowMs, long sleepIntervalMs,
+      int maxGcTimePercentage, GcTimeAlertHandler alertHandler) {
+    Preconditions.checkArgument(observationWindowMs > 0);
+    Preconditions.checkArgument(
+        sleepIntervalMs > 0 && sleepIntervalMs < observationWindowMs);
+    Preconditions.checkArgument(
+        maxGcTimePercentage >= 0 && maxGcTimePercentage <= 100);
+
+    this.observationWindowMs = observationWindowMs;
+    this.sleepIntervalMs = sleepIntervalMs;
+    this.maxGcTimePercentage = maxGcTimePercentage;
+    this.alertHandler = alertHandler;
+
+    bufSize = (int) (observationWindowMs / sleepIntervalMs + 2);
+    // Prevent the user from accidentally creating an abnormally big buffer,
+    // which will result in slow calculations and likely inaccuracy.
+    Preconditions.checkArgument(bufSize <= 128 * 1024);
+    gcDataBuf = new TsAndData[bufSize];
+    for (int i = 0; i < bufSize; i++) {
+      gcDataBuf[i] = new TsAndData();
+    }
+
+    this.setDaemon(true);
+    this.setName("GcTimeMonitor obsWindow = " + observationWindowMs +
+        ", sleepInterval = " + sleepIntervalMs +
+        ", maxGcTimePerc = " + maxGcTimePercentage);
+  }
+
+  @Override
+  public void run() {
+    startTime = System.currentTimeMillis();
+    curData.timestamp = startTime;
+    gcDataBuf[startIdx].setValues(startTime, 0);
+
+    while (shouldRun) {
+      try {
+        Thread.sleep(sleepIntervalMs);
+      } catch (InterruptedException ie) {
+        return;
+      }
+
+      calculateGCTimePercentageWithinObservedInterval();
+      if (alertHandler != null &&
+          curData.gcTimePercentage > maxGcTimePercentage) {
+        alertHandler.alert(curData.clone());
+      }
+    }
+  }
+
+  public void shutdown() {
+    shouldRun = false;
+  }
+
+  /** Returns a copy of the most recent data measured by this monitor. */
+  public GcData getLatestGcData() {
+    return curData.clone();
+  }
+
+  private void calculateGCTimePercentageWithinObservedInterval() {
+    long prevTotalGcTime = curData.totalGcTime;
+    long totalGcTime = 0;
+    long totalGcCount = 0;
+    for (GarbageCollectorMXBean gcBean : gcBeans) {
+      totalGcTime += gcBean.getCollectionTime();
+      totalGcCount += gcBean.getCollectionCount();
+    }
+    long gcTimeWithinSleepInterval = totalGcTime - prevTotalGcTime;
+
+    long ts = System.currentTimeMillis();
+    long gcMonitorRunTime = ts - startTime;
+
+    endIdx = (endIdx + 1) % bufSize;
+    gcDataBuf[endIdx].setValues(ts, gcTimeWithinSleepInterval);
+
+    // Move startIdx forward until we reach the first buffer entry with
+    // timestamp within the observation window.
+    long startObsWindowTs = ts - observationWindowMs;
+    while (gcDataBuf[startIdx].ts < startObsWindowTs && startIdx != endIdx) {
+      startIdx = (startIdx + 1) % bufSize;
+    }
+
+    // Calculate total GC time within observationWindowMs.
+    // We should be careful about GC time that passed before the first timestamp
+    // in our observation window.
+    long gcTimeWithinObservationWindow = Math.min(
+        gcDataBuf[startIdx].gcPause, gcDataBuf[startIdx].ts - startObsWindowTs);
+    if (startIdx != endIdx) {
+      for (int i = (startIdx + 1) % bufSize; i != endIdx;
+           i = (i + 1) % bufSize) {
+        gcTimeWithinObservationWindow += gcDataBuf[i].gcPause;
+      }
+    }
+
+    curData.update(ts, gcMonitorRunTime, totalGcTime, totalGcCount,
+        (int) (gcTimeWithinObservationWindow * 100 /
+          Math.min(observationWindowMs, gcMonitorRunTime)));
+  }
+
+  /**
+   * The user can provide an instance of a class implementing this interface
+   * when initializing a GcTimeMonitor to receive alerts when GC time
+   * percentage exceeds the specified threshold.
+   */
+  public interface GcTimeAlertHandler {
+    void alert(GcData gcData);
+  }
+
+  /** Encapsulates data about GC pauses measured at the specific timestamp. */
+  public static class GcData implements Cloneable {
+    private long timestamp;
+    private long gcMonitorRunTime, totalGcTime, totalGcCount;
+    private int gcTimePercentage;
+
+    /** Returns the absolute timestamp when this measurement was taken. */
+    public long getTimestamp() {
+      return timestamp;
+    }
+
+    /** Returns the time since the start of the associated GcTimeMonitor. */
+    public long getGcMonitorRunTime() {
+      return gcMonitorRunTime;
+    }
+
+    /** Returns accumulated GC time since this JVM started. */
+    public long getAccumulatedGcTime() {
+      return totalGcTime;
+    }
+
+    /** Returns the accumulated number of GC pauses since this JVM started. */
+    public long getAccumulatedGcCount() {
+      return totalGcCount;
+    }
+
+    /**
+     * Returns the percentage (0..100) of time that the JVM spent in GC pauses
+     * within the observation window of the associated GcTimeMonitor.
+     */
+    public int getGcTimePercentage() {
+      return gcTimePercentage;
+    }
+
+    private synchronized void update(long inTimestamp, long inGcMonitorRunTime,
+        long inTotalGcTime, long inTotalGcCount, int inGcTimePercentage) {
+      this.timestamp = inTimestamp;
+      this.gcMonitorRunTime = inGcMonitorRunTime;
+      this.totalGcTime = inTotalGcTime;
+      this.totalGcCount = inTotalGcCount;
+      this.gcTimePercentage = inGcTimePercentage;
+    }
+
+    @Override
+    public synchronized GcData clone() {
+      try {
+        return (GcData) super.clone();
+      } catch (CloneNotSupportedException e) {
+        throw new RuntimeException(e);
+      }
+    }
+  }
+
+  private static class TsAndData {
+    private long ts;      // Timestamp when this measurement was taken
+    private long gcPause; // Total GC pause time within the interval between ts
+                          // and the timestamp of the previous measurement.
+
+    void setValues(long inTs, long inGcPause) {
+      this.ts = inTs;
+      this.gcPause = inGcPause;
+    }
+  }
+}

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/source/TestJvmMetrics.java

@@ -18,6 +18,7 @@
 
 package org.apache.hadoop.metrics2.source;
 
+import org.apache.hadoop.util.GcTimeMonitor;
 import org.junit.After;
 import org.junit.Assert;
 import org.junit.Rule;
@@ -35,6 +36,9 @@ import org.apache.hadoop.service.ServiceStateException;
 import org.apache.hadoop.test.GenericTestUtils;
 import org.apache.hadoop.util.JvmPauseMonitor;
 
+import java.util.ArrayList;
+import java.util.List;
+
 import static org.apache.hadoop.metrics2.source.JvmMetricsInfo.*;
 import static org.apache.hadoop.metrics2.impl.MsInfo.*;
 
@@ -43,17 +47,21 @@ public class TestJvmMetrics {
   @Rule
   public Timeout timeout = new Timeout(30000);
   private JvmPauseMonitor pauseMonitor;
+  private GcTimeMonitor gcTimeMonitor;
 
   /**
-   * Robust shutdown of the pause monitor if it hasn't been stopped already.
+   * Robust shutdown of the monitors if they haven't been stopped already.
    */
   @After
   public void teardown() {
     ServiceOperations.stop(pauseMonitor);
+    if (gcTimeMonitor != null) {
+      gcTimeMonitor.shutdown();
+    }
   }
 
   @Test
-  public void testPresence() {
+  public void testJvmPauseMonitorPresence() {
     pauseMonitor = new JvmPauseMonitor();
     pauseMonitor.init(new Configuration());
     pauseMonitor.start();
@@ -66,16 +74,37 @@ public class TestJvmMetrics {
     verify(rb).tag(ProcessName, "test");
     verify(rb).tag(SessionId, "test");
     for (JvmMetricsInfo info : JvmMetricsInfo.values()) {
-      if (info.name().startsWith("Mem"))
+      if (info.name().startsWith("Mem")) {
         verify(rb).addGauge(eq(info), anyFloat());
-      else if (info.name().startsWith("Gc"))
+      } else if (info.name().startsWith("Gc") &&
+          !info.name().equals("GcTimePercentage")) {
         verify(rb).addCounter(eq(info), anyLong());
-      else if (info.name().startsWith("Threads"))
+      } else if (info.name().startsWith("Threads")) {
         verify(rb).addGauge(eq(info), anyInt());
-      else if (info.name().startsWith("Log"))
+      } else if (info.name().startsWith("Log")) {
         verify(rb).addCounter(eq(info), anyLong());
       }
     }
+  }
+
+  @Test
+  public void testGcTimeMonitorPresence() {
+    gcTimeMonitor = new GcTimeMonitor(60000, 1000, 70, null);
+    gcTimeMonitor.start();
+    JvmMetrics jvmMetrics = new JvmMetrics("test", "test");
+    jvmMetrics.setGcTimeMonitor(gcTimeMonitor);
+    MetricsRecordBuilder rb = getMetrics(jvmMetrics);
+    MetricsCollector mc = rb.parent();
+
+    verify(mc).addRecord(JvmMetrics);
+    verify(rb).tag(ProcessName, "test");
+    verify(rb).tag(SessionId, "test");
+    for (JvmMetricsInfo info : JvmMetricsInfo.values()) {
+      if (info.name().equals("GcTimePercentage")) {
+        verify(rb).addCounter(eq(info), anyInt());
+      }
+    }
+  }
 
   @Test
   public void testDoubleStop() throws Throwable {
@@ -120,4 +149,55 @@ public class TestJvmMetrics {
     }
   }
 
+  @Test
+  public void testGcTimeMonitor() {
+    class Alerter implements GcTimeMonitor.GcTimeAlertHandler {
+      private volatile int numAlerts;
+      private volatile int maxGcTimePercentage;
+      @Override
+      public void alert(GcTimeMonitor.GcData gcData) {
+        numAlerts++;
+        if (gcData.getGcTimePercentage() > maxGcTimePercentage) {
+          maxGcTimePercentage = gcData.getGcTimePercentage();
+        }
+      }
+    }
+    Alerter alerter = new Alerter();
+
+    int alertGcPerc = 10;  // Alerter should be called if GC takes >= 10%
+    gcTimeMonitor = new GcTimeMonitor(60*1000, 100, alertGcPerc, alerter);
+    gcTimeMonitor.start();
+
+    int maxGcTimePercentage = 0;
+    long gcCount = 0;
+
+    // Generate a lot of garbage for some time and verify that the monitor
+    // reports at least some percentage of time in GC pauses, and that the
+    // alerter is invoked at least once.
+
+    List<String> garbageStrings = new ArrayList<>();
+
+    long startTime = System.currentTimeMillis();
+    // Run this for at least 1 sec for our monitor to collect enough data
+    while (System.currentTimeMillis() - startTime < 1000) {
+      for (int j = 0; j < 100000; j++) {
+        garbageStrings.add(
+            "Long string prefix just to fill memory with garbage " + j);
+      }
+      garbageStrings.clear();
+      System.gc();
+
+      GcTimeMonitor.GcData gcData = gcTimeMonitor.getLatestGcData();
+      int gcTimePercentage = gcData.getGcTimePercentage();
+      if (gcTimePercentage > maxGcTimePercentage) {
+        maxGcTimePercentage = gcTimePercentage;
+      }
+      gcCount = gcData.getAccumulatedGcCount();
+    }
+
+    Assert.assertTrue(maxGcTimePercentage > 0);
+    Assert.assertTrue(gcCount > 0);
+    Assert.assertTrue(alerter.numAlerts > 0);
+    Assert.assertTrue(alerter.maxGcTimePercentage >= alertGcPerc);
+  }
 }