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/*
* Copyright 2012-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Amazon Software License (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/asl/
*
* or in the "license" file accompanying this file. This file 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 com.amazonaws.services.kinesis.leases.impl;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import com.amazonaws.services.cloudwatch.model.StandardUnit;
import com.amazonaws.services.kinesis.leases.exceptions.DependencyException;
import com.amazonaws.services.kinesis.leases.exceptions.InvalidStateException;
import com.amazonaws.services.kinesis.leases.exceptions.ProvisionedThroughputException;
import com.amazonaws.services.kinesis.leases.interfaces.ILeaseManager;
import com.amazonaws.services.kinesis.leases.interfaces.ILeaseTaker;
import com.amazonaws.services.kinesis.metrics.impl.MetricsHelper;
import com.amazonaws.services.kinesis.metrics.interfaces.IMetricsScope;
import com.amazonaws.services.kinesis.metrics.interfaces.MetricsLevel;
/**
* An implementation of ILeaseTaker that uses DynamoDB via LeaseManager.
*/
public class LeaseTaker implements ILeaseTaker {
private static final Log LOG = LogFactory.getLog(LeaseTaker.class);
private static final int TAKE_RETRIES = 3;
private static final int SCAN_RETRIES = 1;
// See note on takeLeases(Callable) for why we have this callable.
private static final Callable SYSTEM_CLOCK_CALLABLE = new Callable() {
@Override
public Long call() {
return System.nanoTime();
}
};
private final ILeaseManager leaseManager;
private final String workerIdentifier;
private final Map allLeases = new HashMap();
private final long leaseDurationNanos;
private int maxLeasesForWorker = Integer.MAX_VALUE;
private int maxLeasesToStealAtOneTime = 1;
private long lastScanTimeNanos = 0L;
public LeaseTaker(ILeaseManager leaseManager, String workerIdentifier, long leaseDurationMillis) {
this.leaseManager = leaseManager;
this.workerIdentifier = workerIdentifier;
this.leaseDurationNanos = TimeUnit.MILLISECONDS.toNanos(leaseDurationMillis);
}
/**
* Worker will not acquire more than the specified max number of leases even if there are more
* shards that need to be processed. This can be used in scenarios where a worker is resource constrained or
* to prevent lease thrashing when small number of workers pick up all leases for small amount of time during
* deployment.
* Note that setting a low value may cause data loss (e.g. if there aren't enough Workers to make progress on all
* shards). When setting the value for this property, one must ensure enough workers are present to process
* shards and should consider future resharding, child shards that may be blocked on parent shards, some workers
* becoming unhealthy, etc.
*
* @param maxLeasesForWorker Max leases this Worker can handle at a time
* @return LeaseTaker
*/
public LeaseTaker withMaxLeasesForWorker(int maxLeasesForWorker) {
if (maxLeasesForWorker <= 0) {
throw new IllegalArgumentException("maxLeasesForWorker should be >= 1");
}
this.maxLeasesForWorker = maxLeasesForWorker;
return this;
}
/**
* Max leases to steal from a more loaded Worker at one time (for load balancing).
* Setting this to a higher number can allow for faster load convergence (e.g. during deployments, cold starts),
* but can cause higher churn in the system.
*
* @param maxLeasesToStealAtOneTime Steal up to this many leases at one time (for load balancing)
* @return LeaseTaker
*/
public LeaseTaker withMaxLeasesToStealAtOneTime(int maxLeasesToStealAtOneTime) {
if (maxLeasesToStealAtOneTime <= 0) {
throw new IllegalArgumentException("maxLeasesToStealAtOneTime should be >= 1");
}
this.maxLeasesToStealAtOneTime = maxLeasesToStealAtOneTime;
return this;
}
/**
* {@inheritDoc}
*/
@Override
public Map takeLeases() throws DependencyException, InvalidStateException {
return takeLeases(SYSTEM_CLOCK_CALLABLE);
}
/**
* Internal implementation of takeLeases. Takes a callable that can provide the time to enable test cases without
* Thread.sleep. Takes a callable instead of a raw time value because the time needs to be computed as-of
* immediately after the scan.
*
* @param timeProvider Callable that will supply the time
*
* @return map of lease key to taken lease
*
* @throws DependencyException
* @throws InvalidStateException
*/
synchronized Map takeLeases(Callable timeProvider)
throws DependencyException, InvalidStateException {
// Key is leaseKey
Map takenLeases = new HashMap();
long startTime = System.currentTimeMillis();
boolean success = false;
ProvisionedThroughputException lastException = null;
try {
for (int i = 1; i <= SCAN_RETRIES; i++) {
try {
updateAllLeases(timeProvider);
success = true;
} catch (ProvisionedThroughputException e) {
LOG.info(String.format("Worker %s could not find expired leases on try %d out of %d",
workerIdentifier,
i,
TAKE_RETRIES));
lastException = e;
}
}
} finally {
MetricsHelper.addSuccessAndLatency("ListLeases", startTime, success, MetricsLevel.DETAILED);
}
if (lastException != null) {
LOG.error("Worker " + workerIdentifier
+ " could not scan leases table, aborting takeLeases. Exception caught by last retry:",
lastException);
return takenLeases;
}
List expiredLeases = getExpiredLeases();
Set leasesToTake = computeLeasesToTake(expiredLeases);
Set untakenLeaseKeys = new HashSet();
for (T lease : leasesToTake) {
String leaseKey = lease.getLeaseKey();
startTime = System.currentTimeMillis();
success = false;
try {
for (int i = 1; i <= TAKE_RETRIES; i++) {
try {
if (leaseManager.takeLease(lease, workerIdentifier)) {
lease.setLastCounterIncrementNanos(System.nanoTime());
takenLeases.put(leaseKey, lease);
} else {
untakenLeaseKeys.add(leaseKey);
}
success = true;
break;
} catch (ProvisionedThroughputException e) {
LOG.info(String.format("Could not take lease with key %s for worker %s on try %d out of %d due to capacity",
leaseKey,
workerIdentifier,
i,
TAKE_RETRIES));
}
}
} finally {
MetricsHelper.addSuccessAndLatency("TakeLease", startTime, success, MetricsLevel.DETAILED);
}
}
if (takenLeases.size() > 0) {
LOG.info(String.format("Worker %s successfully took %d leases: %s",
workerIdentifier,
takenLeases.size(),
stringJoin(takenLeases.keySet(), ", ")));
}
if (untakenLeaseKeys.size() > 0) {
LOG.info(String.format("Worker %s failed to take %d leases: %s",
workerIdentifier,
untakenLeaseKeys.size(),
stringJoin(untakenLeaseKeys, ", ")));
}
MetricsHelper.getMetricsScope().addData(
"TakenLeases", takenLeases.size(), StandardUnit.Count, MetricsLevel.SUMMARY);
return takenLeases;
}
/** Package access for testing purposes.
*
* @param strings
* @param delimiter
* @return Joined string.
*/
static String stringJoin(Collection strings, String delimiter) {
StringBuilder builder = new StringBuilder();
boolean needDelimiter = false;
for (String string : strings) {
if (needDelimiter) {
builder.append(delimiter);
}
builder.append(string);
needDelimiter = true;
}
return builder.toString();
}
/**
* Scan all leases and update lastRenewalTime. Add new leases and delete old leases.
*
* @param timeProvider callable that supplies the current time
*
* @return list of expired leases, possibly empty, never null.
*
* @throws ProvisionedThroughputException if listLeases fails due to lack of provisioned throughput
* @throws InvalidStateException if the lease table does not exist
* @throws DependencyException if listLeases fails in an unexpected way
*/
private void updateAllLeases(Callable timeProvider)
throws DependencyException, InvalidStateException, ProvisionedThroughputException {
List freshList = leaseManager.listLeases();
try {
lastScanTimeNanos = timeProvider.call();
} catch (Exception e) {
throw new DependencyException("Exception caught from timeProvider", e);
}
// This set will hold the lease keys not updated by the previous listLeases call.
Set notUpdated = new HashSet(allLeases.keySet());
// Iterate over all leases, finding ones to try to acquire that haven't changed since the last iteration
for (T lease : freshList) {
String leaseKey = lease.getLeaseKey();
T oldLease = allLeases.get(leaseKey);
allLeases.put(leaseKey, lease);
notUpdated.remove(leaseKey);
if (oldLease != null) {
// If we've seen this lease before...
if (oldLease.getLeaseCounter().equals(lease.getLeaseCounter())) {
// ...and the counter hasn't changed, propagate the lastRenewalNanos time from the old lease
lease.setLastCounterIncrementNanos(oldLease.getLastCounterIncrementNanos());
} else {
// ...and the counter has changed, set lastRenewalNanos to the time of the scan.
lease.setLastCounterIncrementNanos(lastScanTimeNanos);
}
} else {
if (lease.getLeaseOwner() == null) {
// if this new lease is unowned, it's never been renewed.
lease.setLastCounterIncrementNanos(0L);
if (LOG.isDebugEnabled()) {
LOG.debug("Treating new lease with key " + leaseKey
+ " as never renewed because it is new and unowned.");
}
} else {
// if this new lease is owned, treat it as renewed as of the scan
lease.setLastCounterIncrementNanos(lastScanTimeNanos);
if (LOG.isDebugEnabled()) {
LOG.debug("Treating new lease with key " + leaseKey
+ " as recently renewed because it is new and owned.");
}
}
}
}
// Remove dead leases from allLeases
for (String key : notUpdated) {
allLeases.remove(key);
}
}
/**
* @return list of leases that were expired as of our last scan.
*/
private List getExpiredLeases() {
List expiredLeases = new ArrayList();
for (T lease : allLeases.values()) {
if (lease.isExpired(leaseDurationNanos, lastScanTimeNanos)) {
expiredLeases.add(lease);
}
}
return expiredLeases;
}
/**
* Compute the number of leases I should try to take based on the state of the system.
*
* @param allLeases map of shardId to lease containing all leases
* @param expiredLeases list of leases we determined to be expired
* @return set of leases to take.
*/
private Set computeLeasesToTake(List expiredLeases) {
Map leaseCounts = computeLeaseCounts(expiredLeases);
Set leasesToTake = new HashSet();
IMetricsScope metrics = MetricsHelper.getMetricsScope();
int numLeases = allLeases.size();
int numWorkers = leaseCounts.size();
if (numLeases == 0) {
// If there are no leases, I shouldn't try to take any.
return leasesToTake;
}
int target;
if (numWorkers >= numLeases) {
// If we have n leases and n or more workers, each worker can have up to 1 lease, including myself.
target = 1;
} else {
/*
* numWorkers must be < numLeases.
*
* Our target for each worker is numLeases / numWorkers (+1 if numWorkers doesn't evenly divide numLeases)
*/
target = numLeases / numWorkers + (numLeases % numWorkers == 0 ? 0 : 1);
// Spill over is the number of leases this worker should have claimed, but did not because it would
// exceed the max allowed for this worker.
int leaseSpillover = Math.max(0, target - maxLeasesForWorker);
if (target > maxLeasesForWorker) {
LOG.warn(String.format("Worker %s target is %d leases and maxLeasesForWorker is %d."
+ " Resetting target to %d, lease spillover is %d. "
+ " Note that some shards may not be processed if no other workers are able to pick them up.",
workerIdentifier,
target,
maxLeasesForWorker,
maxLeasesForWorker,
leaseSpillover));
target = maxLeasesForWorker;
}
metrics.addData("LeaseSpillover", leaseSpillover, StandardUnit.Count, MetricsLevel.SUMMARY);
}
int myCount = leaseCounts.get(workerIdentifier);
int numLeasesToReachTarget = target - myCount;
if (numLeasesToReachTarget <= 0) {
// If we don't need anything, return the empty set.
return leasesToTake;
}
// Shuffle expiredLeases so workers don't all try to contend for the same leases.
Collections.shuffle(expiredLeases);
int originalExpiredLeasesSize = expiredLeases.size();
if (expiredLeases.size() > 0) {
// If we have expired leases, get up to leases from expiredLeases
for (; numLeasesToReachTarget > 0 && expiredLeases.size() > 0; numLeasesToReachTarget--) {
leasesToTake.add(expiredLeases.remove(0));
}
} else {
// If there are no expired leases and we need a lease, consider stealing.
List leasesToSteal = chooseLeasesToSteal(leaseCounts, numLeasesToReachTarget, target);
for (T leaseToSteal : leasesToSteal) {
LOG.info(String.format("Worker %s needed %d leases but none were expired, so it will steal lease %s from %s",
workerIdentifier,
numLeasesToReachTarget,
leaseToSteal.getLeaseKey(),
leaseToSteal.getLeaseOwner()));
leasesToTake.add(leaseToSteal);
}
}
if (!leasesToTake.isEmpty()) {
LOG.info(String.format("Worker %s saw %d total leases, %d available leases, %d "
+ "workers. Target is %d leases, I have %d leases, I will take %d leases",
workerIdentifier,
numLeases,
originalExpiredLeasesSize,
numWorkers,
target,
myCount,
leasesToTake.size()));
}
metrics.addData("TotalLeases", numLeases, StandardUnit.Count, MetricsLevel.DETAILED);
metrics.addData("ExpiredLeases", originalExpiredLeasesSize, StandardUnit.Count, MetricsLevel.SUMMARY);
metrics.addData("NumWorkers", numWorkers, StandardUnit.Count, MetricsLevel.SUMMARY);
metrics.addData("NeededLeases", numLeasesToReachTarget, StandardUnit.Count, MetricsLevel.DETAILED);
metrics.addData("LeasesToTake", leasesToTake.size(), StandardUnit.Count, MetricsLevel.DETAILED);
return leasesToTake;
}
/**
* Choose leases to steal by randomly selecting one or more (up to max) from the most loaded worker.
* Stealing rules:
*
* Steal up to maxLeasesToStealAtOneTime leases from the most loaded worker if
* a) he has > target leases and I need >= 1 leases : steal min(leases needed, maxLeasesToStealAtOneTime)
* b) he has == target leases and I need > 1 leases : steal 1
*
* @param leaseCounts map of workerIdentifier to lease count
* @param needed # of leases needed to reach the target leases for the worker
* @param target target # of leases per worker
* @return Leases to steal, or empty list if we should not steal
*/
private List chooseLeasesToSteal(Map leaseCounts, int needed, int target) {
List leasesToSteal = new ArrayList<>();
Entry mostLoadedWorker = null;
// Find the most loaded worker
for (Entry worker : leaseCounts.entrySet()) {
if (mostLoadedWorker == null || mostLoadedWorker.getValue() < worker.getValue()) {
mostLoadedWorker = worker;
}
}
int numLeasesToSteal = 0;
if ((mostLoadedWorker.getValue() >= target) && (needed > 0)) {
int leasesOverTarget = mostLoadedWorker.getValue() - target;
numLeasesToSteal = Math.min(needed, leasesOverTarget);
// steal 1 if we need > 1 and max loaded worker has target leases.
if ((needed > 1) && (numLeasesToSteal == 0)) {
numLeasesToSteal = 1;
}
numLeasesToSteal = Math.min(numLeasesToSteal, maxLeasesToStealAtOneTime);
}
if (numLeasesToSteal <= 0) {
if (LOG.isDebugEnabled()) {
LOG.debug(String.format("Worker %s not stealing from most loaded worker %s. He has %d,"
+ " target is %d, and I need %d",
workerIdentifier,
mostLoadedWorker.getKey(),
mostLoadedWorker.getValue(),
target,
needed));
}
return leasesToSteal;
} else {
if (LOG.isDebugEnabled()) {
LOG.debug(String.format("Worker %s will attempt to steal %d leases from most loaded worker %s. "
+ " He has %d leases, target is %d, I need %d, maxLeasesToSteatAtOneTime is %d.",
workerIdentifier,
numLeasesToSteal,
mostLoadedWorker.getKey(),
mostLoadedWorker.getValue(),
target,
needed,
maxLeasesToStealAtOneTime));
}
}
String mostLoadedWorkerIdentifier = mostLoadedWorker.getKey();
List candidates = new ArrayList();
// Collect leases belonging to that worker
for (T lease : allLeases.values()) {
if (mostLoadedWorkerIdentifier.equals(lease.getLeaseOwner())) {
candidates.add(lease);
}
}
// Return random ones
Collections.shuffle(candidates);
int toIndex = Math.min(candidates.size(), numLeasesToSteal);
leasesToSteal.addAll(candidates.subList(0, toIndex));
return leasesToSteal;
}
/**
* Count leases by host. Always includes myself, but otherwise only includes hosts that are currently holding
* leases.
*
* @param expiredLeases list of leases that are currently expired
* @return map of workerIdentifier to lease count
*/
private Map computeLeaseCounts(List expiredLeases) {
Map leaseCounts = new HashMap();
// Compute the number of leases per worker by looking through allLeases and ignoring leases that have expired.
for (T lease : allLeases.values()) {
if (!expiredLeases.contains(lease)) {
String leaseOwner = lease.getLeaseOwner();
Integer oldCount = leaseCounts.get(leaseOwner);
if (oldCount == null) {
leaseCounts.put(leaseOwner, 1);
} else {
leaseCounts.put(leaseOwner, oldCount + 1);
}
}
}
// If I have no leases, I wasn't represented in leaseCounts. Let's fix that.
Integer myCount = leaseCounts.get(workerIdentifier);
if (myCount == null) {
myCount = 0;
leaseCounts.put(workerIdentifier, myCount);
}
return leaseCounts;
}
/**
* {@inheritDoc}
*/
@Override
public String getWorkerIdentifier() {
return workerIdentifier;
}
}
