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/**
* 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 callCounts =
new ConcurrentHashMap();
// 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> scheduleCacheRef =
new AtomicReference>();
// 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 schedulerRef;
private Timer timer;
public DecayTask(DecayRpcScheduler scheduler, Timer timer) {
this.schedulerRef = new WeakReference(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 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> it =
callCounts.entrySet().iterator();
while (it.hasNext()) {
Map.Entry 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 nextCache = new HashMap();
for (Map.Entry 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 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 getCallCountSnapshot() {
HashMap snapshot = new HashMap();
for (Map.Entry 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 INSTANCES =
new HashMap();
// Weakref for delegate, so we don't retain it forever if it can be GC'd
private WeakReference 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(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 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();
}
}
}
