src/java/org/apache/cassandra/locator/DynamicEndpointSnitch.java - cassandra - Git at Google

 /**
  * 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.cassandra.locator;

 import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;

 import com.codahale.metrics.ExponentiallyDecayingReservoir;

 import com.codahale.metrics.Snapshot;
 import org.apache.cassandra.concurrent.ScheduledExecutors;
 import org.apache.cassandra.config.DatabaseDescriptor;
 import org.apache.cassandra.net.MessagingService;
 import org.apache.cassandra.service.StorageService;
 import org.apache.cassandra.utils.FBUtilities;
 import org.apache.cassandra.utils.MBeanWrapper;


 /**
  * A dynamic snitch that sorts endpoints by latency with an adapted phi failure detector
  */
 public class DynamicEndpointSnitch extends AbstractEndpointSnitch implements ILatencySubscriber, DynamicEndpointSnitchMBean
 {
     private static final boolean USE_SEVERITY = !Boolean.getBoolean("cassandra.ignore_dynamic_snitch_severity");

     private static final double ALPHA = 0.75; // set to 0.75 to make EDS more biased to towards the newer values
     private static final int WINDOW_SIZE = 100;

     private final int UPDATE_INTERVAL_IN_MS = DatabaseDescriptor.getDynamicUpdateInterval();
     private final int RESET_INTERVAL_IN_MS = DatabaseDescriptor.getDynamicResetInterval();
     private final double BADNESS_THRESHOLD = DatabaseDescriptor.getDynamicBadnessThreshold();

     // the score for a merged set of endpoints must be this much worse than the score for separate endpoints to
     // warrant not merging two ranges into a single range
     private double RANGE_MERGING_PREFERENCE = 1.5;

     private String mbeanName;
     private boolean registered = false;

     private volatile HashMap<InetAddress, Double> scores = new HashMap<>();
     private final ConcurrentHashMap<InetAddress, ExponentiallyDecayingReservoir> samples = new ConcurrentHashMap<>();

     public final IEndpointSnitch subsnitch;

     public DynamicEndpointSnitch(IEndpointSnitch snitch)
     {
         this(snitch, null);
     }
     public DynamicEndpointSnitch(IEndpointSnitch snitch, String instance)
     {
         mbeanName = "org.apache.cassandra.db:type=DynamicEndpointSnitch";
         if (instance != null)
             mbeanName += ",instance=" + instance;
         subsnitch = snitch;
         Runnable update = new Runnable()
         {
             public void run()
             {
                 updateScores();
             }
         };
         Runnable reset = new Runnable()
         {
             public void run()
             {
                 // we do this so that a host considered bad has a chance to recover, otherwise would we never try
                 // to read from it, which would cause its score to never change
                 reset();
             }
         };
         ScheduledExecutors.scheduledTasks.scheduleWithFixedDelay(update, UPDATE_INTERVAL_IN_MS, UPDATE_INTERVAL_IN_MS, TimeUnit.MILLISECONDS);
         ScheduledExecutors.scheduledTasks.scheduleWithFixedDelay(reset, RESET_INTERVAL_IN_MS, RESET_INTERVAL_IN_MS, TimeUnit.MILLISECONDS);
         registerMBean();
    }

     private void registerMBean()
     {
         MBeanWrapper.instance.registerMBean(this, mbeanName);
     }

     public void unregisterMBean()
     {
         MBeanWrapper.instance.unregisterMBean(mbeanName);
     }

     @Override
     public void gossiperStarting()
     {
         subsnitch.gossiperStarting();
     }

     public String getRack(InetAddress endpoint)
     {
         return subsnitch.getRack(endpoint);
     }

     public String getDatacenter(InetAddress endpoint)
     {
         return subsnitch.getDatacenter(endpoint);
     }

     public List<InetAddress> getSortedListByProximity(final InetAddress address, Collection<InetAddress> addresses)
     {
         List<InetAddress> list = new ArrayList<InetAddress>(addresses);
         sortByProximity(address, list);
         return list;
     }

     @Override
     public void sortByProximity(final InetAddress address, List<InetAddress> addresses)
     {
         assert address.equals(FBUtilities.getBroadcastAddress()); // we only know about ourself
         if (BADNESS_THRESHOLD == 0)
         {
             sortByProximityWithScore(address, addresses);
         }
         else
         {
             sortByProximityWithBadness(address, addresses);
         }
     }

     private void sortByProximityWithScore(final InetAddress address, List<InetAddress> addresses)
     {
         // Scores can change concurrently from a call to this method. But Collections.sort() expects
         // its comparator to be "stable", that is 2 endpoint should compare the same way for the duration
         // of the sort() call. As we copy the scores map on write, it is thus enough to alias the current
         // version of it during this call.
         final HashMap<InetAddress, Double> scores = this.scores;
         Collections.sort(addresses, new Comparator<InetAddress>()
         {
             public int compare(InetAddress a1, InetAddress a2)
             {
                 return compareEndpoints(address, a1, a2, scores);
             }
         });
     }

     private void sortByProximityWithBadness(final InetAddress address, List<InetAddress> addresses)
     {
         if (addresses.size() < 2)
             return;

         subsnitch.sortByProximity(address, addresses);
         HashMap<InetAddress, Double> scores = this.scores; // Make sure the score don't change in the middle of the loop below
                                                            // (which wouldn't really matter here but its cleaner that way).
         ArrayList<Double> subsnitchOrderedScores = new ArrayList<>(addresses.size());
         for (InetAddress inet : addresses)
         {
             Double score = scores.get(inet);
             if (score == null)
                 continue;
             subsnitchOrderedScores.add(score);
         }

         // Sort the scores and then compare them (positionally) to the scores in the subsnitch order.
         // If any of the subsnitch-ordered scores exceed the optimal/sorted score by BADNESS_THRESHOLD, use
         // the score-sorted ordering instead of the subsnitch ordering.
         ArrayList<Double> sortedScores = new ArrayList<>(subsnitchOrderedScores);
         Collections.sort(sortedScores);

         Iterator<Double> sortedScoreIterator = sortedScores.iterator();
         for (Double subsnitchScore : subsnitchOrderedScores)
         {
             if (subsnitchScore > (sortedScoreIterator.next() * (1.0 + BADNESS_THRESHOLD)))
             {
                 sortByProximityWithScore(address, addresses);
                 return;
             }
         }
     }

     // Compare endpoints given an immutable snapshot of the scores
     private int compareEndpoints(InetAddress target, InetAddress a1, InetAddress a2, Map<InetAddress, Double> scores)
     {
         Double scored1 = scores.get(a1);
         Double scored2 = scores.get(a2);

         if (scored1 == null)
         {
             scored1 = 0.0;
         }

         if (scored2 == null)
         {
             scored2 = 0.0;
         }

         if (scored1.equals(scored2))
             return subsnitch.compareEndpoints(target, a1, a2);
         if (scored1 < scored2)
             return -1;
         else
             return 1;
     }

     public int compareEndpoints(InetAddress target, InetAddress a1, InetAddress a2)
     {
         // That function is fundamentally unsafe because the scores can change at any time and so the result of that
         // method is not stable for identical arguments. This is why we don't rely on super.sortByProximity() in
         // sortByProximityWithScore().
         throw new UnsupportedOperationException("You shouldn't wrap the DynamicEndpointSnitch (within itself or otherwise)");
     }

     public void receiveTiming(InetAddress host, long latency) // this is cheap
     {
         ExponentiallyDecayingReservoir sample = samples.get(host);
         if (sample == null)
         {
             ExponentiallyDecayingReservoir maybeNewSample = new ExponentiallyDecayingReservoir(WINDOW_SIZE, ALPHA);
             sample = samples.putIfAbsent(host, maybeNewSample);
             if (sample == null)
                 sample = maybeNewSample;
         }
         sample.update(latency);
     }

     private void updateScores() // this is expensive
     {
         if (!StorageService.instance.isInitialized())
             return;
         if (!registered)
         {
             if (MessagingService.instance() != null)
             {
                 MessagingService.instance().register(this);
                 registered = true;
             }

         }
         double maxLatency = 1;

         Map<InetAddress, Snapshot> snapshots = new HashMap<>(samples.size());
         for (Map.Entry<InetAddress, ExponentiallyDecayingReservoir> entry : samples.entrySet())
         {
             snapshots.put(entry.getKey(), entry.getValue().getSnapshot());
         }

         // We're going to weight the latency for each host against the worst one we see, to
         // arrive at sort of a 'badness percentage' for them. First, find the worst for each:
         HashMap<InetAddress, Double> newScores = new HashMap<>();
         for (Map.Entry<InetAddress, Snapshot> entry : snapshots.entrySet())
         {
             double mean = entry.getValue().getMedian();
             if (mean > maxLatency)
                 maxLatency = mean;
         }
         // now make another pass to do the weighting based on the maximums we found before
         for (Map.Entry<InetAddress, Snapshot> entry : snapshots.entrySet())
         {
             double score = entry.getValue().getMedian() / maxLatency;
             // finally, add the severity without any weighting, since hosts scale this relative to their own load and the size of the task causing the severity.
             // "Severity" is basically a measure of compaction activity (CASSANDRA-3722).
             if (USE_SEVERITY)
                 score += StorageService.instance.getSeverity(entry.getKey());
             // lowest score (least amount of badness) wins.
             newScores.put(entry.getKey(), score);
         }
         scores = newScores;
     }

     private void reset()
     {
        samples.clear();
     }

     public Map<InetAddress, Double> getScores()
     {
         return scores;
     }

     public int getUpdateInterval()
     {
         return UPDATE_INTERVAL_IN_MS;
     }
     public int getResetInterval()
     {
         return RESET_INTERVAL_IN_MS;
     }
     public double getBadnessThreshold()
     {
         return BADNESS_THRESHOLD;
     }

     public String getSubsnitchClassName()
     {
         return subsnitch.getClass().getName();
     }

     public List<Double> dumpTimings(String hostname) throws UnknownHostException
     {
         InetAddress host = InetAddress.getByName(hostname);
         ArrayList<Double> timings = new ArrayList<Double>();
         ExponentiallyDecayingReservoir sample = samples.get(host);
         if (sample != null)
         {
             for (double time: sample.getSnapshot().getValues())
                 timings.add(time);
         }
         return timings;
     }

     public void setSeverity(double severity)
     {
         StorageService.instance.reportManualSeverity(severity);
     }

     public double getSeverity()
     {
         return StorageService.instance.getSeverity(FBUtilities.getBroadcastAddress());
     }

     public boolean isWorthMergingForRangeQuery(List<InetAddress> merged, List<InetAddress> l1, List<InetAddress> l2)
     {
         if (!subsnitch.isWorthMergingForRangeQuery(merged, l1, l2))
             return false;

         // skip checking scores in the single-node case
         if (l1.size() == 1 && l2.size() == 1 && l1.get(0).equals(l2.get(0)))
             return true;

         // Make sure we return the subsnitch decision (i.e true if we're here) if we lack too much scores
         double maxMerged = maxScore(merged);
         double maxL1 = maxScore(l1);
         double maxL2 = maxScore(l2);
         if (maxMerged < 0 || maxL1 < 0 || maxL2 < 0)
             return true;

         return maxMerged <= (maxL1 + maxL2) * RANGE_MERGING_PREFERENCE;
     }

     // Return the max score for the endpoint in the provided list, or -1.0 if no node have a score.
     private double maxScore(List<InetAddress> endpoints)
     {
         double maxScore = -1.0;
         for (InetAddress endpoint : endpoints)
         {
             Double score = scores.get(endpoint);
             if (score == null)
                 continue;

             if (score > maxScore)
                 maxScore = score;
         }
         return maxScore;
     }
 }
	/**
	* 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.cassandra.locator;

	import java.net.InetAddress;
	import java.net.UnknownHostException;
	import java.util.*;
	import java.util.concurrent.ConcurrentHashMap;
	import java.util.concurrent.TimeUnit;

	import com.codahale.metrics.ExponentiallyDecayingReservoir;

	import com.codahale.metrics.Snapshot;
	import org.apache.cassandra.concurrent.ScheduledExecutors;
	import org.apache.cassandra.config.DatabaseDescriptor;
	import org.apache.cassandra.net.MessagingService;
	import org.apache.cassandra.service.StorageService;
	import org.apache.cassandra.utils.FBUtilities;
	import org.apache.cassandra.utils.MBeanWrapper;


	/**
	* A dynamic snitch that sorts endpoints by latency with an adapted phi failure detector
	*/
	public class DynamicEndpointSnitch extends AbstractEndpointSnitch implements ILatencySubscriber, DynamicEndpointSnitchMBean
	{
	private static final boolean USE_SEVERITY = !Boolean.getBoolean("cassandra.ignore_dynamic_snitch_severity");

	private static final double ALPHA = 0.75; // set to 0.75 to make EDS more biased to towards the newer values
	private static final int WINDOW_SIZE = 100;

	private final int UPDATE_INTERVAL_IN_MS = DatabaseDescriptor.getDynamicUpdateInterval();
	private final int RESET_INTERVAL_IN_MS = DatabaseDescriptor.getDynamicResetInterval();
	private final double BADNESS_THRESHOLD = DatabaseDescriptor.getDynamicBadnessThreshold();

	// the score for a merged set of endpoints must be this much worse than the score for separate endpoints to
	// warrant not merging two ranges into a single range
	private double RANGE_MERGING_PREFERENCE = 1.5;

	private String mbeanName;
	private boolean registered = false;

	private volatile HashMap<InetAddress, Double> scores = new HashMap<>();
	private final ConcurrentHashMap<InetAddress, ExponentiallyDecayingReservoir> samples = new ConcurrentHashMap<>();

	public final IEndpointSnitch subsnitch;

	public DynamicEndpointSnitch(IEndpointSnitch snitch)
	{
	this(snitch, null);
	}
	public DynamicEndpointSnitch(IEndpointSnitch snitch, String instance)
	{
	mbeanName = "org.apache.cassandra.db:type=DynamicEndpointSnitch";
	if (instance != null)
	mbeanName += ",instance=" + instance;
	subsnitch = snitch;
	Runnable update = new Runnable()
	{
	public void run()
	{
	updateScores();
	}
	};
	Runnable reset = new Runnable()
	{
	public void run()
	{
	// we do this so that a host considered bad has a chance to recover, otherwise would we never try
	// to read from it, which would cause its score to never change
	reset();
	}
	};
	ScheduledExecutors.scheduledTasks.scheduleWithFixedDelay(update, UPDATE_INTERVAL_IN_MS, UPDATE_INTERVAL_IN_MS, TimeUnit.MILLISECONDS);
	ScheduledExecutors.scheduledTasks.scheduleWithFixedDelay(reset, RESET_INTERVAL_IN_MS, RESET_INTERVAL_IN_MS, TimeUnit.MILLISECONDS);
	registerMBean();
	}

	private void registerMBean()
	{
	MBeanWrapper.instance.registerMBean(this, mbeanName);
	}

	public void unregisterMBean()
	{
	MBeanWrapper.instance.unregisterMBean(mbeanName);
	}

	@Override
	public void gossiperStarting()
	{
	subsnitch.gossiperStarting();
	}

	public String getRack(InetAddress endpoint)
	{
	return subsnitch.getRack(endpoint);
	}

	public String getDatacenter(InetAddress endpoint)
	{
	return subsnitch.getDatacenter(endpoint);
	}

	public List<InetAddress> getSortedListByProximity(final InetAddress address, Collection<InetAddress> addresses)
	{
	List<InetAddress> list = new ArrayList<InetAddress>(addresses);
	sortByProximity(address, list);
	return list;
	}

	@Override
	public void sortByProximity(final InetAddress address, List<InetAddress> addresses)
	{
	assert address.equals(FBUtilities.getBroadcastAddress()); // we only know about ourself
	if (BADNESS_THRESHOLD == 0)
	{
	sortByProximityWithScore(address, addresses);
	}
	else
	{
	sortByProximityWithBadness(address, addresses);
	}
	}

	private void sortByProximityWithScore(final InetAddress address, List<InetAddress> addresses)
	{
	// Scores can change concurrently from a call to this method. But Collections.sort() expects
	// its comparator to be "stable", that is 2 endpoint should compare the same way for the duration
	// of the sort() call. As we copy the scores map on write, it is thus enough to alias the current
	// version of it during this call.
	final HashMap<InetAddress, Double> scores = this.scores;
	Collections.sort(addresses, new Comparator<InetAddress>()
	{
	public int compare(InetAddress a1, InetAddress a2)
	{
	return compareEndpoints(address, a1, a2, scores);
	}
	});
	}

	private void sortByProximityWithBadness(final InetAddress address, List<InetAddress> addresses)
	{
	if (addresses.size() < 2)
	return;

	subsnitch.sortByProximity(address, addresses);
	HashMap<InetAddress, Double> scores = this.scores; // Make sure the score don't change in the middle of the loop below
	// (which wouldn't really matter here but its cleaner that way).
	ArrayList<Double> subsnitchOrderedScores = new ArrayList<>(addresses.size());
	for (InetAddress inet : addresses)
	{
	Double score = scores.get(inet);
	if (score == null)
	continue;
	subsnitchOrderedScores.add(score);
	}

	// Sort the scores and then compare them (positionally) to the scores in the subsnitch order.
	// If any of the subsnitch-ordered scores exceed the optimal/sorted score by BADNESS_THRESHOLD, use
	// the score-sorted ordering instead of the subsnitch ordering.
	ArrayList<Double> sortedScores = new ArrayList<>(subsnitchOrderedScores);
	Collections.sort(sortedScores);

	Iterator<Double> sortedScoreIterator = sortedScores.iterator();
	for (Double subsnitchScore : subsnitchOrderedScores)
	{
	if (subsnitchScore > (sortedScoreIterator.next() * (1.0 + BADNESS_THRESHOLD)))
	{
	sortByProximityWithScore(address, addresses);
	return;
	}
	}
	}

	// Compare endpoints given an immutable snapshot of the scores
	private int compareEndpoints(InetAddress target, InetAddress a1, InetAddress a2, Map<InetAddress, Double> scores)
	{
	Double scored1 = scores.get(a1);
	Double scored2 = scores.get(a2);

	if (scored1 == null)
	{
	scored1 = 0.0;
	}

	if (scored2 == null)
	{
	scored2 = 0.0;
	}

	if (scored1.equals(scored2))
	return subsnitch.compareEndpoints(target, a1, a2);
	if (scored1 < scored2)
	return -1;
	else
	return 1;
	}

	public int compareEndpoints(InetAddress target, InetAddress a1, InetAddress a2)
	{
	// That function is fundamentally unsafe because the scores can change at any time and so the result of that
	// method is not stable for identical arguments. This is why we don't rely on super.sortByProximity() in
	// sortByProximityWithScore().
	throw new UnsupportedOperationException("You shouldn't wrap the DynamicEndpointSnitch (within itself or otherwise)");
	}

	public void receiveTiming(InetAddress host, long latency) // this is cheap
	{
	ExponentiallyDecayingReservoir sample = samples.get(host);
	if (sample == null)
	{
	ExponentiallyDecayingReservoir maybeNewSample = new ExponentiallyDecayingReservoir(WINDOW_SIZE, ALPHA);
	sample = samples.putIfAbsent(host, maybeNewSample);
	if (sample == null)
	sample = maybeNewSample;
	}
	sample.update(latency);
	}

	private void updateScores() // this is expensive
	{
	if (!StorageService.instance.isInitialized())
	return;
	if (!registered)
	{
	if (MessagingService.instance() != null)
	{
	MessagingService.instance().register(this);
	registered = true;
	}

	}
	double maxLatency = 1;

	Map<InetAddress, Snapshot> snapshots = new HashMap<>(samples.size());
	for (Map.Entry<InetAddress, ExponentiallyDecayingReservoir> entry : samples.entrySet())
	{
	snapshots.put(entry.getKey(), entry.getValue().getSnapshot());
	}

	// We're going to weight the latency for each host against the worst one we see, to
	// arrive at sort of a 'badness percentage' for them. First, find the worst for each:
	HashMap<InetAddress, Double> newScores = new HashMap<>();
	for (Map.Entry<InetAddress, Snapshot> entry : snapshots.entrySet())
	{
	double mean = entry.getValue().getMedian();
	if (mean > maxLatency)
	maxLatency = mean;
	}
	// now make another pass to do the weighting based on the maximums we found before
	for (Map.Entry<InetAddress, Snapshot> entry : snapshots.entrySet())
	{
	double score = entry.getValue().getMedian() / maxLatency;
	// finally, add the severity without any weighting, since hosts scale this relative to their own load and the size of the task causing the severity.
	// "Severity" is basically a measure of compaction activity (CASSANDRA-3722).
	if (USE_SEVERITY)
	score += StorageService.instance.getSeverity(entry.getKey());
	// lowest score (least amount of badness) wins.
	newScores.put(entry.getKey(), score);
	}
	scores = newScores;
	}

	private void reset()
	{
	samples.clear();
	}

	public Map<InetAddress, Double> getScores()
	{
	return scores;
	}

	public int getUpdateInterval()
	{
	return UPDATE_INTERVAL_IN_MS;
	}
	public int getResetInterval()
	{
	return RESET_INTERVAL_IN_MS;
	}
	public double getBadnessThreshold()
	{
	return BADNESS_THRESHOLD;
	}

	public String getSubsnitchClassName()
	{
	return subsnitch.getClass().getName();
	}

	public List<Double> dumpTimings(String hostname) throws UnknownHostException
	{
	InetAddress host = InetAddress.getByName(hostname);
	ArrayList<Double> timings = new ArrayList<Double>();
	ExponentiallyDecayingReservoir sample = samples.get(host);
	if (sample != null)
	{
	for (double time: sample.getSnapshot().getValues())
	timings.add(time);
	}
	return timings;
	}

	public void setSeverity(double severity)
	{
	StorageService.instance.reportManualSeverity(severity);
	}

	public double getSeverity()
	{
	return StorageService.instance.getSeverity(FBUtilities.getBroadcastAddress());
	}

	public boolean isWorthMergingForRangeQuery(List<InetAddress> merged, List<InetAddress> l1, List<InetAddress> l2)
	{
	if (!subsnitch.isWorthMergingForRangeQuery(merged, l1, l2))
	return false;

	// skip checking scores in the single-node case
	if (l1.size() == 1 && l2.size() == 1 && l1.get(0).equals(l2.get(0)))
	return true;

	// Make sure we return the subsnitch decision (i.e true if we're here) if we lack too much scores
	double maxMerged = maxScore(merged);
	double maxL1 = maxScore(l1);
	double maxL2 = maxScore(l2);
	if (maxMerged < 0 \|\| maxL1 < 0 \|\| maxL2 < 0)
	return true;

	return maxMerged <= (maxL1 + maxL2) * RANGE_MERGING_PREFERENCE;
	}

	// Return the max score for the endpoint in the provided list, or -1.0 if no node have a score.
	private double maxScore(List<InetAddress> endpoints)
	{
	double maxScore = -1.0;
	for (InetAddress endpoint : endpoints)
	{
	Double score = scores.get(endpoint);
	if (score == null)
	continue;

	if (score > maxScore)
	maxScore = score;
	}
	return maxScore;
	}
	}