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HostSelectionWithFallback.java
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HostSelectionWithFallback.java
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/*******************************************************************************
* Copyright 2011 Netflix
*
* Licensed 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 com.netflix.dyno.connectionpool.impl.lb;
import com.netflix.dyno.connectionpool.BaseOperation;
import com.netflix.dyno.connectionpool.Connection;
import com.netflix.dyno.connectionpool.ConnectionPoolConfiguration;
import com.netflix.dyno.connectionpool.ConnectionPoolConfiguration.LoadBalancingStrategy;
import com.netflix.dyno.connectionpool.ConnectionPoolMonitor;
import com.netflix.dyno.connectionpool.HashPartitioner;
import com.netflix.dyno.connectionpool.Host;
import com.netflix.dyno.connectionpool.HostConnectionPool;
import com.netflix.dyno.connectionpool.RetryPolicy;
import com.netflix.dyno.connectionpool.TokenMapSupplier;
import com.netflix.dyno.connectionpool.TokenPoolTopology;
import com.netflix.dyno.connectionpool.TokenRackMapper;
import com.netflix.dyno.connectionpool.exception.DynoConnectException;
import com.netflix.dyno.connectionpool.exception.DynoException;
import com.netflix.dyno.connectionpool.exception.NoAvailableHostsException;
import com.netflix.dyno.connectionpool.exception.PoolExhaustedException;
import com.netflix.dyno.connectionpool.exception.PoolOfflineException;
import com.netflix.dyno.connectionpool.exception.PoolTimeoutException;
import com.netflix.dyno.connectionpool.impl.HostSelectionStrategy;
import com.netflix.dyno.connectionpool.impl.HostSelectionStrategy.HostSelectionStrategyFactory;
import com.netflix.dyno.connectionpool.impl.RunOnce;
import com.netflix.dyno.connectionpool.impl.utils.CollectionUtils;
import com.netflix.dyno.connectionpool.impl.utils.CollectionUtils.Predicate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;
import java.util.stream.Collectors;
/**
* Acts as a coordinator over multiple HostSelectionStrategy implementations, where each maps to a particular rack.
* This class doesn't actually implement the logic (e.g Round Robin or Token Aware) to borrow the connections. It
* relies on a local HostSelectionStrategy implementation and a collection of remote HostSelectionStrategy(s).
* It gives preference to the "local" HostSelectionStrategy but if the local pool is offline or hosts are down etc, then
* it falls back to the remote HostSelectionStrategy. Also it uses pure round robin for distributing load on the fall
* back HostSelectionStrategy implementations for even distribution of load on the remote racks in the event of an
* outage in the local rack.
* <p>
* Note that this class does not prefer any one remote HostSelectionStrategy over another.
*
* @param <CL>
* @author poberai
* @author jcacciatore
*/
public class HostSelectionWithFallback<CL> {
private static final Logger logger = LoggerFactory.getLogger(HostSelectionWithFallback.class);
// Only used in calculating replication factor
private final String localDataCenter;
// tracks the local zone
private final String localRack;
// The selector for the local zone
private final HostSelectionStrategy<CL> localSelector;
// Track selectors for each remote zone
private final ConcurrentHashMap<String, HostSelectionStrategy<CL>> remoteRackSelectors = new ConcurrentHashMap<>();
private final ConcurrentHashMap<Host, HostToken> hostTokens = new ConcurrentHashMap<>();
private final TokenMapSupplier tokenSupplier;
private final ConnectionPoolConfiguration cpConfig;
private final ConnectionPoolMonitor cpMonitor;
private final AtomicInteger replicationFactor = new AtomicInteger(-1);
// Represents the *initial* topology from the token supplier. This does not affect selection of a host connection
// pool for traffic. It only affects metrics such as failover/fallback
private final AtomicReference<TokenPoolTopology> topology = new AtomicReference<>(null);
// list of names of remote zones. Used for RoundRobin over remote zones when local zone host is down
private final CircularList<String> remoteRackNames = new CircularList<>(new ArrayList<>());
private final HostSelectionStrategyFactory<CL> selectorFactory;
public HostSelectionWithFallback(ConnectionPoolConfiguration config, ConnectionPoolMonitor monitor) {
cpMonitor = monitor;
cpConfig = config;
localRack = cpConfig.getLocalRack();
localDataCenter = cpConfig.getLocalDataCenter();
tokenSupplier = cpConfig.getTokenSupplier();
selectorFactory = new DefaultSelectionFactory(cpConfig);
localSelector = selectorFactory.vendPoolSelectionStrategy();
}
public Connection<CL> getConnection(BaseOperation<CL, ?> op, int duration, TimeUnit unit) throws NoAvailableHostsException, PoolExhaustedException {
return getConnection(op, null, duration, unit, cpConfig.getRetryPolicyFactory().getRetryPolicy());
}
public Connection<CL> getConnectionUsingRetryPolicy(BaseOperation<CL, ?> op, int duration, TimeUnit unit, RetryPolicy retry) throws NoAvailableHostsException, PoolExhaustedException {
return getConnection(op, null, duration, unit, retry);
}
private Connection<CL> getConnection(BaseOperation<CL, ?> op, Long token, int duration, TimeUnit unit, RetryPolicy retry)
throws NoAvailableHostsException, PoolExhaustedException, PoolTimeoutException, PoolOfflineException {
DynoConnectException lastEx = null;
HostConnectionPool<CL> hostPool = null;
if (retry.getAttemptCount() == 0 || (retry.getAttemptCount() > 0 && !retry.allowCrossZoneFallback())) {
// By default zone affinity is enabled; if the local rack is not known at startup it is disabled
if (cpConfig.localZoneAffinity()) {
hostPool = getHostPoolForOperationOrTokenInLocalZone(op, token);
} else {
hostPool = getFallbackHostPool(op, token);
}
}
if (hostPool != null) {
try {
// Note that if a PoolExhaustedException is thrown it is caught by the calling
// ConnectionPoolImpl#executeXXX() method
return hostPool.borrowConnection(duration, unit);
} catch (PoolTimeoutException pte) {
lastEx = pte;
cpMonitor.incOperationFailure(null, pte);
}
}
if (attemptFallback()) {
if (topology.get().getTokensForRack(localRack) != null) {
cpMonitor.incFailover(null, lastEx);
}
hostPool = getFallbackHostPool(op, token);
if (hostPool != null) {
return hostPool.borrowConnection(duration, unit);
}
}
if (lastEx == null) {
throw new PoolOfflineException(hostPool == null ? null : hostPool.getHost(), "host pool is offline and no Racks available for fallback");
} else {
throw lastEx;
}
}
// Should be called when a connection is required on that particular zone with no fall backs what so ever
private Connection<CL> getConnectionForTokenOnRackNoFallback(BaseOperation<CL, ?> op, Long token, String rack, int duration, TimeUnit unit, RetryPolicy retry)
throws NoAvailableHostsException, PoolExhaustedException, PoolTimeoutException, PoolOfflineException {
DynoConnectException lastEx = null;
// find the selector for that rack,
HostSelectionStrategy<CL> selector = findSelectorForRack(rack);
// get the host using that selector
HostConnectionPool<CL> hostPool = selector.getPoolForToken(token);
if (hostPool != null) {
try {
// Note that if a PoolExhaustedException is thrown it is caught by the calling
// ConnectionPoolImpl#executeXXX() method
return hostPool.borrowConnection(duration, unit);
} catch (PoolTimeoutException pte) {
lastEx = pte;
cpMonitor.incOperationFailure(null, pte);
}
}
if (lastEx == null) {
throw new PoolOfflineException(hostPool == null ? null : hostPool.getHost(), "host pool is offline and we are forcing no fallback");
} else {
throw lastEx;
}
}
private HostConnectionPool<CL> getHostPoolForOperationOrTokenInLocalZone(BaseOperation<CL, ?> op, Long token) {
HostConnectionPool<CL> hostPool;
try {
if (!localSelector.isEmpty()) {
hostPool = (op != null) ? localSelector.getPoolForOperation(op, cpConfig.getHashtag()) : localSelector.getPoolForToken(token);
if (isConnectionPoolActive(hostPool)) {
return hostPool;
}
}
} catch (NoAvailableHostsException e) {
cpMonitor.incOperationFailure(null, e);
}
return null;
}
private boolean attemptFallback() {
return cpConfig.getMaxFailoverCount() > 0 &&
(cpConfig.localZoneAffinity() && remoteRackNames.getEntireList().size() > 0) ||
(!cpConfig.localZoneAffinity() && !localSelector.isEmpty());
}
private HostConnectionPool<CL> getFallbackHostPool(BaseOperation<CL, ?> op, Long token) {
int numRemotes = remoteRackNames.getEntireList().size();
if (numRemotes == 0) {
throw new NoAvailableHostsException("Could not find any remote Racks for fallback");
}
int numTries = Math.min(numRemotes, cpConfig.getMaxFailoverCount());
DynoException lastEx = null;
while ((numTries > 0)) {
numTries--;
String remoteRack = remoteRackNames.getNextElement();
HostSelectionStrategy<CL> remoteRackSelector = remoteRackSelectors.get(remoteRack);
try {
HostConnectionPool<CL> fallbackHostPool =
(op != null) ? remoteRackSelector.getPoolForOperation(op, cpConfig.getHashtag()) : remoteRackSelector.getPoolForToken(token);
if (isConnectionPoolActive(fallbackHostPool)) {
return fallbackHostPool;
}
} catch (NoAvailableHostsException e) {
cpMonitor.incOperationFailure(null, e);
lastEx = e;
}
}
if (lastEx != null) {
throw lastEx;
} else {
throw new NoAvailableHostsException("Local rack host offline and could not find any remote hosts for fallback connection");
}
}
public Collection<Connection<CL>> getConnectionsToRing(TokenRackMapper tokenRackMapper, int duration, TimeUnit unit) throws NoAvailableHostsException, PoolExhaustedException {
String targetRack = localRack;
if (targetRack == null) {
// get tokens for random rack
targetRack = topology.get().getRandomRack();
}
final Set<Long> tokens = topology.get().getTokenHostsForRack(targetRack).keySet();
DynoConnectException lastEx = null;
final List<Connection<CL>> connections = new ArrayList<>();
for (Long token : tokens) {
try {
// Cursor has a map of token to rack which indicates an affinity to a zone for that token.
// This is valid in case of an iterator based query like scan.
// Try to use that same rack if it is specified.
String rack = null;
if (tokenRackMapper != null)
rack = tokenRackMapper.getRackForToken(token);
if (rack != null) {
connections.add(getConnectionForTokenOnRackNoFallback(null, token, rack, duration, unit, new RunOnce()));
} else {
Connection<CL> c = getConnection(null, token, duration, unit, new RunOnce());
if (tokenRackMapper != null) {
tokenRackMapper.setRackForToken(token, c.getHost().getRack());
}
connections.add(c);
}
} catch (DynoConnectException e) {
logger.warn("Failed to get connection when getting all connections from ring", e.getMessage());
lastEx = e;
break;
}
}
if (lastEx != null) {
// Return all previously borrowed connection to avoid any connection leaks
for (Connection<CL> connection : connections) {
try {
connection.getParentConnectionPool().returnConnection(connection);
} catch (DynoConnectException e) {
// do nothing
}
}
throw lastEx;
} else {
return connections;
}
}
private HostSelectionStrategy<CL> findSelectorForRack(String rack) {
if (localRack == null) {
return localSelector;
}
if (localRack.equals(rack)) {
return localSelector;
}
HostSelectionStrategy<CL> remoteSelector = remoteRackSelectors.get(rack);
return remoteSelector;
}
private boolean isConnectionPoolActive(HostConnectionPool<CL> hPool) {
if (hPool == null) {
return false;
}
Host host = hPool.getHost();
return host.isUp() && hPool.isActive();
}
private Map<HostToken, HostConnectionPool<CL>> getHostPoolsForRack(final Map<HostToken, HostConnectionPool<CL>> map, final String rack) {
Map<HostToken, HostConnectionPool<CL>> dcPools =
CollectionUtils.filterKeys(map, new Predicate<HostToken>() {
@Override
public boolean apply(HostToken x) {
if (localRack == null) {
return true;
}
return rack.equals(x.getHost().getRack());
}
});
return dcPools;
}
/**
* Initialize the topology with the host pools obtained from discovery.
* hPools comes from discovery.
*
* @param hPools
*/
public void initWithHosts(Map<Host, HostConnectionPool<CL>> hPools) {
// Get the list of tokens for these hosts
//tokenSupplier.initWithHosts(hPools.keySet());
List<HostToken> allHostTokens = tokenSupplier.getTokens(hPools.keySet());
Map<HostToken, HostConnectionPool<CL>> tokenPoolMap = new HashMap<HostToken, HostConnectionPool<CL>>();
// Update inner state with the host tokens.
for (HostToken hToken : allHostTokens) {
hostTokens.put(hToken.getHost(), hToken);
tokenPoolMap.put(hToken, hPools.get(hToken.getHost()));
}
// Initialize Local selector
Map<HostToken, HostConnectionPool<CL>> localPools = getHostPoolsForRack(tokenPoolMap, localRack);
localSelector.initWithHosts(localPools);
if (localSelector.isTokenAware()) {
replicationFactor.set(HostUtils.calculateReplicationFactorForDC(allHostTokens, cpConfig.getLocalDataCenter(), localRack));
}
// Initialize Remote selectors
Set<String> remoteRacks = hPools.keySet().stream().map(h -> h.getRack()).filter(rack -> rack != null && !rack.equals(localRack)).collect(Collectors.toSet());
for (String rack : remoteRacks) {
Map<HostToken, HostConnectionPool<CL>> dcPools = getHostPoolsForRack(tokenPoolMap, rack);
HostSelectionStrategy<CL> remoteSelector = selectorFactory.vendPoolSelectionStrategy();
remoteSelector.initWithHosts(dcPools);
remoteRackSelectors.put(rack, remoteSelector);
}
remoteRackNames.swapWithList(remoteRackSelectors.keySet());
topology.set(createTokenPoolTopology(allHostTokens));
}
/**
* Calculate replication factor from the given list of hosts
*
* @param allHostTokens
* @return replicationFactor
*/
int calculateReplicationFactor(List<HostToken> allHostTokens) {
return HostUtils.calculateReplicationFactorForDC(allHostTokens, null, localRack);
}
public void addHost(Host host, HostConnectionPool<CL> hostPool) {
HostToken hostToken = tokenSupplier.getTokenForHost(host, hostTokens.keySet());
if (hostToken == null) {
throw new DynoConnectException("Could not find host token for host: " + host);
}
hostTokens.put(hostToken.getHost(), hostToken);
HostSelectionStrategy<CL> selector = findSelectorForRack(host.getRack());
if (selector != null) {
selector.addHostPool(hostToken, hostPool);
}
topology.get().addHostToken(hostToken.getHost().getRack(), hostToken.getToken(), hostToken.getHost());
}
public void removeHost(Host host) {
HostToken hostToken = hostTokens.remove(host);
if (hostToken != null) {
HostSelectionStrategy<CL> selector = findSelectorForRack(host.getRack());
if (selector != null) {
selector.removeHostPool(hostToken);
}
topology.get().removeHost(hostToken.getHost().getRack(), hostToken.getToken(), hostToken.getHost());
}
}
private class DefaultSelectionFactory implements HostSelectionStrategyFactory<CL> {
private final LoadBalancingStrategy lbStrategy;
private final HashPartitioner hashPartitioner;
private DefaultSelectionFactory(ConnectionPoolConfiguration config) {
lbStrategy = config.getLoadBalancingStrategy();
hashPartitioner = config.getHashPartitioner();
}
@Override
public HostSelectionStrategy<CL> vendPoolSelectionStrategy() {
switch (lbStrategy) {
case RoundRobin:
return new RoundRobinSelection<CL>();
case TokenAware:
return hashPartitioner != null
? new TokenAwareSelection<CL>(hashPartitioner)
: new TokenAwareSelection<CL>();
default:
throw new RuntimeException("LoadBalancing strategy not supported! " + cpConfig.getLoadBalancingStrategy().name());
}
}
}
private void updateTokenPoolTopology(TokenPoolTopology topology) {
if (localRack != null) {
addTokens(topology, localRack, localSelector);
}
for (String remoteRack : remoteRackSelectors.keySet()) {
addTokens(topology, remoteRack, remoteRackSelectors.get(remoteRack));
}
}
/**
* Create token pool topology from the host tokens
*
* @param allHostTokens
* @return tokenPoolTopology with the host information
*/
public TokenPoolTopology createTokenPoolTopology(List<HostToken> allHostTokens) {
TokenPoolTopology topology = new TokenPoolTopology(replicationFactor.get());
for (HostToken hostToken : allHostTokens) {
String rack = hostToken.getHost().getRack();
topology.addHostToken(rack, hostToken.getToken(), hostToken.getHost());
}
updateTokenPoolTopology(topology);
return topology;
}
public TokenPoolTopology getTokenPoolTopology() {
TokenPoolTopology topology = new TokenPoolTopology(replicationFactor.get());
updateTokenPoolTopology(topology);
return topology;
}
private void addTokens(TokenPoolTopology topology, String rack, HostSelectionStrategy<CL> selectionStrategy) {
Collection<HostConnectionPool<CL>> pools = selectionStrategy.getOrderedHostPools();
for (HostConnectionPool<CL> pool : pools) {
if (pool == null) {
continue;
}
HostToken hToken = hostTokens.get(pool.getHost());
if (hToken == null) {
continue;
}
topology.addToken(rack, hToken.getToken(), pool);
}
}
public Long getTokenForKey(String key) {
return localSelector.getTokenForKey(key).getToken();
}
@Override
public String toString() {
return "HostSelectionWithFallback{" +
"localDataCenter='" + localDataCenter + '\'' +
", localRack='" + localRack + '\'' +
", localSelector=" + localSelector +
", remoteRackSelectors=" + remoteRackSelectors +
", hostTokens=" + hostTokens +
", tokenSupplier=" + tokenSupplier +
", cpConfig=" + cpConfig +
", cpMonitor=" + cpMonitor +
", replicationFactor=" + replicationFactor +
", topology=" + topology +
", remoteRackNames=" + remoteRackNames +
", selectorFactory=" + selectorFactory +
'}';
}
}