HADOOP-10281. Create a scheduler, which assigns schedulables a priority level. (Contributed by Chris Li)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1617643 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -505,6 +505,9 @@ Release 2.6.0 - UNRELEASED
     HADOOP-10820. Throw an exception in GenericOptionsParser when passed
     an empty Path. (Alex Holmes and Zhihai Xu via wang)
 
+    HADOOP-10281. Create a scheduler, which assigns schedulables a priority
+    level. (Chris Li via Arpit Agarwal)
+
   OPTIMIZATIONS
 
   BUG FIXES

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/DecayRpcScheduler.java

@@ -0,0 +1,522 @@
+/**
+ * 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.ipc;
+
+import java.lang.ref.WeakReference;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Timer;
+import java.util.TimerTask;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeys;
+import org.apache.hadoop.metrics2.util.MBeans;
+
+import org.codehaus.jackson.map.ObjectMapper;
+import com.google.common.annotations.VisibleForTesting;
+
+/**
+ * The decay RPC scheduler counts incoming requests in a map, then
+ * decays the counts at a fixed time interval. The scheduler is optimized
+ * for large periods (on the order of seconds), as it offloads work to the
+ * decay sweep.
+ */
+public class DecayRpcScheduler implements RpcScheduler, DecayRpcSchedulerMXBean {
+  /**
+   * Period controls how many milliseconds between each decay sweep.
+   */
+  public static final String IPC_CALLQUEUE_DECAYSCHEDULER_PERIOD_KEY =
+    "faircallqueue.decay-scheduler.period-ms";
+  public static final long   IPC_CALLQUEUE_DECAYSCHEDULER_PERIOD_DEFAULT =
+    5000L;
+
+  /**
+   * Decay factor controls how much each count is suppressed by on each sweep.
+   * Valid numbers are > 0 and < 1. Decay factor works in tandem with period
+   * to control how long the scheduler remembers an identity.
+   */
+  public static final String IPC_CALLQUEUE_DECAYSCHEDULER_FACTOR_KEY =
+    "faircallqueue.decay-scheduler.decay-factor";
+  public static final double IPC_CALLQUEUE_DECAYSCHEDULER_FACTOR_DEFAULT =
+    0.5;
+
+  /**
+   * Thresholds are specified as integer percentages, and specify which usage
+   * range each queue will be allocated to. For instance, specifying the list
+   *  10, 40, 80
+   * implies 4 queues, with
+   * - q3 from 80% up
+   * - q2 from 40 up to 80
+   * - q1 from 10 up to 40
+   * - q0 otherwise.
+   */
+  public static final String IPC_CALLQUEUE_DECAYSCHEDULER_THRESHOLDS_KEY =
+    "faircallqueue.decay-scheduler.thresholds";
+
+  // Specifies the identity to use when the IdentityProvider cannot handle
+  // a schedulable.
+  public static final String DECAYSCHEDULER_UNKNOWN_IDENTITY =
+    "IdentityProvider.Unknown";
+
+  public static final Log LOG = LogFactory.getLog(DecayRpcScheduler.class);
+
+  // Track the number of calls for each schedulable identity
+  private final ConcurrentHashMap<Object, AtomicLong> callCounts =
+    new ConcurrentHashMap<Object, AtomicLong>();
+
+  // Should be the sum of all AtomicLongs in callCounts
+  private final AtomicLong totalCalls = new AtomicLong();
+
+  // Pre-computed scheduling decisions during the decay sweep are
+  // atomically swapped in as a read-only map
+  private final AtomicReference<Map<Object, Integer>> scheduleCacheRef =
+    new AtomicReference<Map<Object, Integer>>();
+
+  // Tune the behavior of the scheduler
+  private final long decayPeriodMillis; // How long between each tick
+  private final double decayFactor; // nextCount = currentCount / decayFactor
+  private final int numQueues; // affects scheduling decisions, from 0 to numQueues - 1
+  private final double[] thresholds;
+  private final IdentityProvider identityProvider;
+
+  /**
+   * This TimerTask will call decayCurrentCounts until
+   * the scheduler has been garbage collected.
+   */
+  public static class DecayTask extends TimerTask {
+    private WeakReference<DecayRpcScheduler> schedulerRef;
+    private Timer timer;
+
+    public DecayTask(DecayRpcScheduler scheduler, Timer timer) {
+      this.schedulerRef = new WeakReference<DecayRpcScheduler>(scheduler);
+      this.timer = timer;
+    }
+
+    @Override
+    public void run() {
+      DecayRpcScheduler sched = schedulerRef.get();
+      if (sched != null) {
+        sched.decayCurrentCounts();
+      } else {
+        // Our scheduler was garbage collected since it is no longer in use,
+        // so we should terminate the timer as well
+        timer.cancel();
+        timer.purge();
+      }
+    }
+  }
+
+  /**
+   * Create a decay scheduler.
+   * @param numQueues number of queues to schedule for
+   * @param ns config prefix, so that we can configure multiple schedulers
+   *           in a single instance.
+   * @param conf configuration to use.
+   */
+  public DecayRpcScheduler(int numQueues, String ns, Configuration conf) {
+    if (numQueues < 1) {
+      throw new IllegalArgumentException("number of queues must be > 0");
+    }
+
+    this.numQueues = numQueues;
+    this.decayFactor = parseDecayFactor(ns, conf);
+    this.decayPeriodMillis = parseDecayPeriodMillis(ns, conf);
+    this.identityProvider = this.parseIdentityProvider(ns, conf);
+    this.thresholds = parseThresholds(ns, conf, numQueues);
+
+    // Setup delay timer
+    Timer timer = new Timer();
+    DecayTask task = new DecayTask(this, timer);
+    timer.scheduleAtFixedRate(task, 0, this.decayPeriodMillis);
+
+    MetricsProxy prox = MetricsProxy.getInstance(ns);
+    prox.setDelegate(this);
+  }
+
+  // Load configs
+  private IdentityProvider parseIdentityProvider(String ns, Configuration conf) {
+    List<IdentityProvider> providers = conf.getInstances(
+      ns + "." + CommonConfigurationKeys.IPC_CALLQUEUE_IDENTITY_PROVIDER_KEY,
+      IdentityProvider.class);
+
+    if (providers.size() < 1) {
+      LOG.info("IdentityProvider not specified, " +
+        "defaulting to UserIdentityProvider");
+      return new UserIdentityProvider();
+    }
+
+    return providers.get(0); // use the first
+  }
+
+  private static double parseDecayFactor(String ns, Configuration conf) {
+    double factor = conf.getDouble(ns + "." +
+        IPC_CALLQUEUE_DECAYSCHEDULER_FACTOR_KEY,
+      IPC_CALLQUEUE_DECAYSCHEDULER_FACTOR_DEFAULT
+    );
+
+    if (factor <= 0 || factor >= 1) {
+      throw new IllegalArgumentException("Decay Factor " +
+        "must be between 0 and 1");
+    }
+
+    return factor;
+  }
+
+  private static long parseDecayPeriodMillis(String ns, Configuration conf) {
+    long period = conf.getLong(ns + "." +
+        IPC_CALLQUEUE_DECAYSCHEDULER_PERIOD_KEY,
+      IPC_CALLQUEUE_DECAYSCHEDULER_PERIOD_DEFAULT
+    );
+
+    if (period <= 0) {
+      throw new IllegalArgumentException("Period millis must be >= 0");
+    }
+
+    return period;
+  }
+
+  private static double[] parseThresholds(String ns, Configuration conf,
+      int numQueues) {
+    int[] percentages = conf.getInts(ns + "." +
+      IPC_CALLQUEUE_DECAYSCHEDULER_THRESHOLDS_KEY);
+
+    if (percentages.length == 0) {
+      return getDefaultThresholds(numQueues);
+    } else if (percentages.length != numQueues-1) {
+      throw new IllegalArgumentException("Number of thresholds should be " +
+        (numQueues-1) + ". Was: " + percentages.length);
+    }
+
+    // Convert integer percentages to decimals
+    double[] decimals = new double[percentages.length];
+    for (int i = 0; i < percentages.length; i++) {
+      decimals[i] = percentages[i] / 100.0;
+    }
+
+    return decimals;
+  }
+
+  /**
+   * Generate default thresholds if user did not specify. Strategy is
+   * to halve each time, since queue usage tends to be exponential.
+   * So if numQueues is 4, we would generate: double[]{0.125, 0.25, 0.5}
+   * which specifies the boundaries between each queue's usage.
+   * @param numQueues number of queues to compute for
+   * @return array of boundaries of length numQueues - 1
+   */
+  private static double[] getDefaultThresholds(int numQueues) {
+    double[] ret = new double[numQueues - 1];
+    double div = Math.pow(2, numQueues - 1);
+
+    for (int i = 0; i < ret.length; i++) {
+      ret[i] = Math.pow(2, i)/div;
+    }
+    return ret;
+  }
+
+  /**
+   * Decay the stored counts for each user and clean as necessary.
+   * This method should be called periodically in order to keep
+   * counts current.
+   */
+  private void decayCurrentCounts() {
+    long total = 0;
+    Iterator<Map.Entry<Object, AtomicLong>> it =
+      callCounts.entrySet().iterator();
+
+    while (it.hasNext()) {
+      Map.Entry<Object, AtomicLong> entry = it.next();
+      AtomicLong count = entry.getValue();
+
+      // Compute the next value by reducing it by the decayFactor
+      long currentValue = count.get();
+      long nextValue = (long)(currentValue * decayFactor);
+      total += nextValue;
+      count.set(nextValue);
+
+      if (nextValue == 0) {
+        // We will clean up unused keys here. An interesting optimization might
+        // be to have an upper bound on keyspace in callCounts and only
+        // clean once we pass it.
+        it.remove();
+      }
+    }
+
+    // Update the total so that we remain in sync
+    totalCalls.set(total);
+
+    // Now refresh the cache of scheduling decisions
+    recomputeScheduleCache();
+  }
+
+  /**
+   * Update the scheduleCache to match current conditions in callCounts.
+   */
+  private void recomputeScheduleCache() {
+    Map<Object, Integer> nextCache = new HashMap<Object, Integer>();
+
+    for (Map.Entry<Object, AtomicLong> entry : callCounts.entrySet()) {
+      Object id = entry.getKey();
+      AtomicLong value = entry.getValue();
+
+      long snapshot = value.get();
+      int computedLevel = computePriorityLevel(snapshot);
+
+      nextCache.put(id, computedLevel);
+    }
+
+    // Swap in to activate
+    scheduleCacheRef.set(Collections.unmodifiableMap(nextCache));
+  }
+
+  /**
+   * Get the number of occurrences and increment atomically.
+   * @param identity the identity of the user to increment
+   * @return the value before incrementation
+   */
+  private long getAndIncrement(Object identity) throws InterruptedException {
+    // We will increment the count, or create it if no such count exists
+    AtomicLong count = this.callCounts.get(identity);
+    if (count == null) {
+      // Create the count since no such count exists.
+      count = new AtomicLong(0);
+
+      // Put it in, or get the AtomicInteger that was put in by another thread
+      AtomicLong otherCount = callCounts.putIfAbsent(identity, count);
+      if (otherCount != null) {
+        count = otherCount;
+      }
+    }
+
+    // Update the total
+    totalCalls.getAndIncrement();
+
+    // At this point value is guaranteed to be not null. It may however have
+    // been clobbered from callCounts. Nonetheless, we return what
+    // we have.
+    return count.getAndIncrement();
+  }
+
+  /**
+   * Given the number of occurrences, compute a scheduling decision.
+   * @param occurrences how many occurrences
+   * @return scheduling decision from 0 to numQueues - 1
+   */
+  private int computePriorityLevel(long occurrences) {
+    long totalCallSnapshot = totalCalls.get();
+
+    double proportion = 0;
+    if (totalCallSnapshot > 0) {
+      proportion = (double) occurrences / totalCallSnapshot;
+    }
+
+    // Start with low priority queues, since they will be most common
+    for(int i = (numQueues - 1); i > 0; i--) {
+      if (proportion >= this.thresholds[i - 1]) {
+        return i; // We've found our queue number
+      }
+    }
+
+    // If we get this far, we're at queue 0
+    return 0;
+  }
+
+  /**
+   * Returns the priority level for a given identity by first trying the cache,
+   * then computing it.
+   * @param identity an object responding to toString and hashCode
+   * @return integer scheduling decision from 0 to numQueues - 1
+   */
+  private int cachedOrComputedPriorityLevel(Object identity) {
+    try {
+      long occurrences = this.getAndIncrement(identity);
+
+      // Try the cache
+      Map<Object, Integer> scheduleCache = scheduleCacheRef.get();
+      if (scheduleCache != null) {
+        Integer priority = scheduleCache.get(identity);
+        if (priority != null) {
+          return priority;
+        }
+      }
+
+      // Cache was no good, compute it
+      return computePriorityLevel(occurrences);
+    } catch (InterruptedException ie) {
+      LOG.warn("Caught InterruptedException, returning low priority queue");
+      return numQueues - 1;
+    }
+  }
+
+  /**
+   * Compute the appropriate priority for a schedulable based on past requests.
+   * @param obj the schedulable obj to query and remember
+   * @return the queue index which we recommend scheduling in
+   */
+  @Override
+  public int getPriorityLevel(Schedulable obj) {
+    // First get the identity
+    String identity = this.identityProvider.makeIdentity(obj);
+    if (identity == null) {
+      // Identity provider did not handle this
+      identity = DECAYSCHEDULER_UNKNOWN_IDENTITY;
+    }
+
+    return cachedOrComputedPriorityLevel(identity);
+  }
+
+  // For testing
+  @VisibleForTesting
+  public double getDecayFactor() { return decayFactor; }
+
+  @VisibleForTesting
+  public long getDecayPeriodMillis() { return decayPeriodMillis; }
+
+  @VisibleForTesting
+  public double[] getThresholds() { return thresholds; }
+
+  @VisibleForTesting
+  public void forceDecay() { decayCurrentCounts(); }
+
+  @VisibleForTesting
+  public Map<Object, Long> getCallCountSnapshot() {
+    HashMap<Object, Long> snapshot = new HashMap<Object, Long>();
+
+    for (Map.Entry<Object, AtomicLong> entry : callCounts.entrySet()) {
+      snapshot.put(entry.getKey(), entry.getValue().get());
+    }
+
+    return Collections.unmodifiableMap(snapshot);
+  }
+
+  @VisibleForTesting
+  public long getTotalCallSnapshot() {
+    return totalCalls.get();
+  }
+
+  /**
+   * MetricsProxy is a singleton because we may init multiple schedulers and we
+   * want to clean up resources when a new scheduler replaces the old one.
+   */
+  private static final class MetricsProxy implements DecayRpcSchedulerMXBean {
+    // One singleton per namespace
+    private static final HashMap<String, MetricsProxy> INSTANCES =
+      new HashMap<String, MetricsProxy>();
+
+    // Weakref for delegate, so we don't retain it forever if it can be GC'd
+    private WeakReference<DecayRpcScheduler> delegate;
+
+    private MetricsProxy(String namespace) {
+      MBeans.register(namespace, "DecayRpcScheduler", this);
+    }
+
+    public static synchronized MetricsProxy getInstance(String namespace) {
+      MetricsProxy mp = INSTANCES.get(namespace);
+      if (mp == null) {
+        // We must create one
+        mp = new MetricsProxy(namespace);
+        INSTANCES.put(namespace, mp);
+      }
+      return mp;
+    }
+
+    public void setDelegate(DecayRpcScheduler obj) {
+      this.delegate = new WeakReference<DecayRpcScheduler>(obj);
+    }
+
+    @Override
+    public String getSchedulingDecisionSummary() {
+      DecayRpcScheduler scheduler = delegate.get();
+      if (scheduler == null) {
+        return "No Active Scheduler";
+      } else {
+        return scheduler.getSchedulingDecisionSummary();
+      }
+    }
+
+    @Override
+    public String getCallVolumeSummary() {
+      DecayRpcScheduler scheduler = delegate.get();
+      if (scheduler == null) {
+        return "No Active Scheduler";
+      } else {
+        return scheduler.getCallVolumeSummary();
+      }
+    }
+
+    @Override
+    public int getUniqueIdentityCount() {
+      DecayRpcScheduler scheduler = delegate.get();
+      if (scheduler == null) {
+        return -1;
+      } else {
+        return scheduler.getUniqueIdentityCount();
+      }
+    }
+
+    @Override
+    public long getTotalCallVolume() {
+      DecayRpcScheduler scheduler = delegate.get();
+      if (scheduler == null) {
+        return -1;
+      } else {
+        return scheduler.getTotalCallVolume();
+      }
+    }
+  }
+
+  public int getUniqueIdentityCount() {
+    return callCounts.size();
+  }
+
+  public long getTotalCallVolume() {
+    return totalCalls.get();
+  }
+
+  public String getSchedulingDecisionSummary() {
+    Map<Object, Integer> decisions = scheduleCacheRef.get();
+    if (decisions == null) {
+      return "{}";
+    } else {
+      try {
+        ObjectMapper om = new ObjectMapper();
+        return om.writeValueAsString(decisions);
+      } catch (Exception e) {
+        return "Error: " + e.getMessage();
+      }
+    }
+  }
+
+  public String getCallVolumeSummary() {
+    try {
+      ObjectMapper om = new ObjectMapper();
+      return om.writeValueAsString(callCounts);
+    } catch (Exception e) {
+      return "Error: " + e.getMessage();
+    }
+  }
+}

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/DecayRpcSchedulerMXBean.java

@@ -0,0 +1,30 @@
+/**
+ * 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.ipc;
+
+/**
+ * Provides metrics for Decay scheduler.
+ */
+public interface DecayRpcSchedulerMXBean {
+  // Get an overview of the requests in history.
+  String getSchedulingDecisionSummary();
+  String getCallVolumeSummary();
+  int getUniqueIdentityCount();
+  long getTotalCallVolume();
+}

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/RpcScheduler.java

@@ -0,0 +1,29 @@
+/**
+ * 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.ipc;
+
+/**
+ * Implement this interface to be used for RPC scheduling in the fair call queues.
+ */
+public interface RpcScheduler {
+  /**
+   * Returns priority level greater than zero as a hint for scheduling.
+   */
+  int getPriorityLevel(Schedulable obj);
+}

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/ipc/TestDecayRpcScheduler.java

@@ -0,0 +1,225 @@
+/**
+ * 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.ipc;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.Arrays;
+import org.junit.Test;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import org.apache.hadoop.security.UserGroupInformation;
+import org.apache.hadoop.conf.Configuration;
+
+import org.apache.hadoop.fs.CommonConfigurationKeys;
+
+public class TestDecayRpcScheduler {
+  private Schedulable mockCall(String id) {
+    Schedulable mockCall = mock(Schedulable.class);
+    UserGroupInformation ugi = mock(UserGroupInformation.class);
+
+    when(ugi.getUserName()).thenReturn(id);
+    when(mockCall.getUserGroupInformation()).thenReturn(ugi);
+
+    return mockCall;
+  }
+
+  private DecayRpcScheduler scheduler;
+
+  @Test(expected=IllegalArgumentException.class)
+  public void testNegativeScheduler() {
+    scheduler = new DecayRpcScheduler(-1, "", new Configuration());
+  }
+
+  @Test(expected=IllegalArgumentException.class)
+  public void testZeroScheduler() {
+    scheduler = new DecayRpcScheduler(0, "", new Configuration());
+  }
+
+  @Test
+  public void testParsePeriod() {
+    // By default
+    scheduler = new DecayRpcScheduler(1, "", new Configuration());
+    assertEquals(DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_PERIOD_DEFAULT,
+      scheduler.getDecayPeriodMillis());
+
+    // Custom
+    Configuration conf = new Configuration();
+    conf.setLong("ns." + DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_PERIOD_KEY,
+      1058);
+    scheduler = new DecayRpcScheduler(1, "ns", conf);
+    assertEquals(1058L, scheduler.getDecayPeriodMillis());
+  }
+
+  @Test
+  public void testParseFactor() {
+    // Default
+    scheduler = new DecayRpcScheduler(1, "", new Configuration());
+    assertEquals(DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_FACTOR_DEFAULT,
+      scheduler.getDecayFactor(), 0.00001);
+
+    // Custom
+    Configuration conf = new Configuration();
+    conf.set("prefix." + DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_FACTOR_KEY,
+      "0.125");
+    scheduler = new DecayRpcScheduler(1, "prefix", conf);
+    assertEquals(0.125, scheduler.getDecayFactor(), 0.00001);
+  }
+
+  public void assertEqualDecimalArrays(double[] a, double[] b) {
+    assertEquals(a.length, b.length);
+    for(int i = 0; i < a.length; i++) {
+      assertEquals(a[i], b[i], 0.00001);
+    }
+  }
+
+  @Test
+  public void testParseThresholds() {
+    // Defaults vary by number of queues
+    Configuration conf = new Configuration();
+    scheduler = new DecayRpcScheduler(1, "", conf);
+    assertEqualDecimalArrays(new double[]{}, scheduler.getThresholds());
+
+    scheduler = new DecayRpcScheduler(2, "", conf);
+    assertEqualDecimalArrays(new double[]{0.5}, scheduler.getThresholds());
+
+    scheduler = new DecayRpcScheduler(3, "", conf);
+    assertEqualDecimalArrays(new double[]{0.25, 0.5}, scheduler.getThresholds());
+
+    scheduler = new DecayRpcScheduler(4, "", conf);
+    assertEqualDecimalArrays(new double[]{0.125, 0.25, 0.5}, scheduler.getThresholds());
+
+    // Custom
+    conf = new Configuration();
+    conf.set("ns." + DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_THRESHOLDS_KEY,
+      "1, 10, 20, 50, 85");
+    scheduler = new DecayRpcScheduler(6, "ns", conf);
+    assertEqualDecimalArrays(new double[]{0.01, 0.1, 0.2, 0.5, 0.85}, scheduler.getThresholds());
+  }
+
+  @Test
+  public void testAccumulate() {
+    Configuration conf = new Configuration();
+    conf.set("ns." + DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_PERIOD_KEY, "99999999"); // Never flush
+    scheduler = new DecayRpcScheduler(1, "ns", conf);
+
+    assertEquals(0, scheduler.getCallCountSnapshot().size()); // empty first
+
+    scheduler.getPriorityLevel(mockCall("A"));
+    assertEquals(1, scheduler.getCallCountSnapshot().get("A").longValue());
+    assertEquals(1, scheduler.getCallCountSnapshot().get("A").longValue());
+
+    scheduler.getPriorityLevel(mockCall("A"));
+    scheduler.getPriorityLevel(mockCall("B"));
+    scheduler.getPriorityLevel(mockCall("A"));
+
+    assertEquals(3, scheduler.getCallCountSnapshot().get("A").longValue());
+    assertEquals(1, scheduler.getCallCountSnapshot().get("B").longValue());
+  }
+
+  @Test
+  public void testDecay() {
+    Configuration conf = new Configuration();
+    conf.set("ns." + DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_PERIOD_KEY, "999999999"); // Never
+    conf.set("ns." + DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_FACTOR_KEY, "0.5");
+    scheduler = new DecayRpcScheduler(1, "ns", conf);
+
+    assertEquals(0, scheduler.getTotalCallSnapshot());
+
+    for (int i = 0; i < 4; i++) {
+      scheduler.getPriorityLevel(mockCall("A"));
+    }
+
+    for (int i = 0; i < 8; i++) {
+      scheduler.getPriorityLevel(mockCall("B"));
+    }
+
+    assertEquals(12, scheduler.getTotalCallSnapshot());
+    assertEquals(4, scheduler.getCallCountSnapshot().get("A").longValue());
+    assertEquals(8, scheduler.getCallCountSnapshot().get("B").longValue());
+
+    scheduler.forceDecay();
+
+    assertEquals(6, scheduler.getTotalCallSnapshot());
+    assertEquals(2, scheduler.getCallCountSnapshot().get("A").longValue());
+    assertEquals(4, scheduler.getCallCountSnapshot().get("B").longValue());
+
+    scheduler.forceDecay();
+
+    assertEquals(3, scheduler.getTotalCallSnapshot());
+    assertEquals(1, scheduler.getCallCountSnapshot().get("A").longValue());
+    assertEquals(2, scheduler.getCallCountSnapshot().get("B").longValue());
+
+    scheduler.forceDecay();
+
+    assertEquals(1, scheduler.getTotalCallSnapshot());
+    assertEquals(null, scheduler.getCallCountSnapshot().get("A"));
+    assertEquals(1, scheduler.getCallCountSnapshot().get("B").longValue());
+
+    scheduler.forceDecay();
+
+    assertEquals(0, scheduler.getTotalCallSnapshot());
+    assertEquals(null, scheduler.getCallCountSnapshot().get("A"));
+    assertEquals(null, scheduler.getCallCountSnapshot().get("B"));
+  }
+
+  @Test
+  public void testPriority() {
+    Configuration conf = new Configuration();
+    conf.set("ns." + DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_PERIOD_KEY, "99999999"); // Never flush
+    conf.set("ns." + DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_THRESHOLDS_KEY,
+      "25, 50, 75");
+    scheduler = new DecayRpcScheduler(4, "ns", conf);
+
+    assertEquals(0, scheduler.getPriorityLevel(mockCall("A")));
+    assertEquals(2, scheduler.getPriorityLevel(mockCall("A")));
+    assertEquals(0, scheduler.getPriorityLevel(mockCall("B")));
+    assertEquals(1, scheduler.getPriorityLevel(mockCall("B")));
+    assertEquals(0, scheduler.getPriorityLevel(mockCall("C")));
+    assertEquals(0, scheduler.getPriorityLevel(mockCall("C")));
+    assertEquals(1, scheduler.getPriorityLevel(mockCall("A")));
+    assertEquals(1, scheduler.getPriorityLevel(mockCall("A")));
+    assertEquals(1, scheduler.getPriorityLevel(mockCall("A")));
+    assertEquals(2, scheduler.getPriorityLevel(mockCall("A")));
+  }
+
+  @Test(timeout=2000)
+  public void testPeriodic() throws InterruptedException {
+    Configuration conf = new Configuration();
+    conf.set("ns." + DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_PERIOD_KEY, "10");
+    conf.set("ns." + DecayRpcScheduler.IPC_CALLQUEUE_DECAYSCHEDULER_FACTOR_KEY, "0.5");
+    scheduler = new DecayRpcScheduler(1, "ns", conf);
+
+    assertEquals(10, scheduler.getDecayPeriodMillis());
+    assertEquals(0, scheduler.getTotalCallSnapshot());
+
+    for (int i = 0; i < 64; i++) {
+      scheduler.getPriorityLevel(mockCall("A"));
+    }
+
+    // It should eventually decay to zero
+    while (scheduler.getTotalCallSnapshot() > 0) {
+      Thread.sleep(10);
+    }
+  }
+}