334bd8e2d2cc43de963999feb088dd872d6b5c11
[controller.git] / opendaylight / md-sal / sal-distributed-datastore / src / main / java / org / opendaylight / controller / cluster / datastore / Shard.java
1 /*
2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
3  *
4  * This program and the accompanying materials are made available under the
5  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
6  * and is available at http://www.eclipse.org/legal/epl-v10.html
7  */
8 package org.opendaylight.controller.cluster.datastore;
9
10 import akka.actor.ActorRef;
11 import akka.actor.ActorSelection;
12 import akka.actor.Cancellable;
13 import akka.actor.ExtendedActorSystem;
14 import akka.actor.Props;
15 import akka.actor.Status;
16 import akka.actor.Status.Failure;
17 import akka.serialization.JavaSerializer;
18 import akka.serialization.Serialization;
19 import com.google.common.annotations.VisibleForTesting;
20 import com.google.common.base.Optional;
21 import com.google.common.base.Preconditions;
22 import com.google.common.base.Ticker;
23 import com.google.common.base.Verify;
24 import com.google.common.collect.ImmutableList;
25 import com.google.common.collect.ImmutableMap;
26 import com.google.common.collect.Range;
27 import java.io.IOException;
28 import java.util.Arrays;
29 import java.util.Collection;
30 import java.util.Collections;
31 import java.util.Map;
32 import java.util.concurrent.TimeUnit;
33 import javax.annotation.Nonnull;
34 import javax.annotation.Nullable;
35 import org.opendaylight.controller.cluster.access.ABIVersion;
36 import org.opendaylight.controller.cluster.access.commands.ConnectClientRequest;
37 import org.opendaylight.controller.cluster.access.commands.ConnectClientSuccess;
38 import org.opendaylight.controller.cluster.access.commands.LocalHistoryRequest;
39 import org.opendaylight.controller.cluster.access.commands.NotLeaderException;
40 import org.opendaylight.controller.cluster.access.commands.OutOfSequenceEnvelopeException;
41 import org.opendaylight.controller.cluster.access.commands.TransactionRequest;
42 import org.opendaylight.controller.cluster.access.concepts.ClientIdentifier;
43 import org.opendaylight.controller.cluster.access.concepts.FrontendIdentifier;
44 import org.opendaylight.controller.cluster.access.concepts.LocalHistoryIdentifier;
45 import org.opendaylight.controller.cluster.access.concepts.Request;
46 import org.opendaylight.controller.cluster.access.concepts.RequestEnvelope;
47 import org.opendaylight.controller.cluster.access.concepts.RequestException;
48 import org.opendaylight.controller.cluster.access.concepts.RequestSuccess;
49 import org.opendaylight.controller.cluster.access.concepts.RetiredGenerationException;
50 import org.opendaylight.controller.cluster.access.concepts.RuntimeRequestException;
51 import org.opendaylight.controller.cluster.access.concepts.SliceableMessage;
52 import org.opendaylight.controller.cluster.access.concepts.TransactionIdentifier;
53 import org.opendaylight.controller.cluster.access.concepts.UnsupportedRequestException;
54 import org.opendaylight.controller.cluster.common.actor.CommonConfig;
55 import org.opendaylight.controller.cluster.common.actor.Dispatchers;
56 import org.opendaylight.controller.cluster.common.actor.Dispatchers.DispatcherType;
57 import org.opendaylight.controller.cluster.common.actor.MessageTracker;
58 import org.opendaylight.controller.cluster.common.actor.MessageTracker.Error;
59 import org.opendaylight.controller.cluster.common.actor.MeteringBehavior;
60 import org.opendaylight.controller.cluster.datastore.exceptions.NoShardLeaderException;
61 import org.opendaylight.controller.cluster.datastore.identifiers.ShardIdentifier;
62 import org.opendaylight.controller.cluster.datastore.jmx.mbeans.shard.ShardDataTreeListenerInfoMXBeanImpl;
63 import org.opendaylight.controller.cluster.datastore.jmx.mbeans.shard.ShardMBeanFactory;
64 import org.opendaylight.controller.cluster.datastore.jmx.mbeans.shard.ShardStats;
65 import org.opendaylight.controller.cluster.datastore.messages.AbortTransaction;
66 import org.opendaylight.controller.cluster.datastore.messages.ActorInitialized;
67 import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
68 import org.opendaylight.controller.cluster.datastore.messages.CanCommitTransaction;
69 import org.opendaylight.controller.cluster.datastore.messages.CloseTransactionChain;
70 import org.opendaylight.controller.cluster.datastore.messages.CommitTransaction;
71 import org.opendaylight.controller.cluster.datastore.messages.CreateTransaction;
72 import org.opendaylight.controller.cluster.datastore.messages.CreateTransactionReply;
73 import org.opendaylight.controller.cluster.datastore.messages.ForwardedReadyTransaction;
74 import org.opendaylight.controller.cluster.datastore.messages.GetShardDataTree;
75 import org.opendaylight.controller.cluster.datastore.messages.MakeLeaderLocal;
76 import org.opendaylight.controller.cluster.datastore.messages.OnDemandShardState;
77 import org.opendaylight.controller.cluster.datastore.messages.PeerAddressResolved;
78 import org.opendaylight.controller.cluster.datastore.messages.PersistAbortTransactionPayload;
79 import org.opendaylight.controller.cluster.datastore.messages.ReadyLocalTransaction;
80 import org.opendaylight.controller.cluster.datastore.messages.RegisterDataTreeChangeListener;
81 import org.opendaylight.controller.cluster.datastore.messages.ShardLeaderStateChanged;
82 import org.opendaylight.controller.cluster.datastore.messages.UpdateSchemaContext;
83 import org.opendaylight.controller.cluster.datastore.persisted.AbortTransactionPayload;
84 import org.opendaylight.controller.cluster.datastore.persisted.DatastoreSnapshot;
85 import org.opendaylight.controller.cluster.datastore.persisted.DatastoreSnapshot.ShardSnapshot;
86 import org.opendaylight.controller.cluster.messaging.MessageAssembler;
87 import org.opendaylight.controller.cluster.messaging.MessageSlicer;
88 import org.opendaylight.controller.cluster.messaging.SliceOptions;
89 import org.opendaylight.controller.cluster.notifications.LeaderStateChanged;
90 import org.opendaylight.controller.cluster.notifications.RegisterRoleChangeListener;
91 import org.opendaylight.controller.cluster.notifications.RoleChangeNotifier;
92 import org.opendaylight.controller.cluster.raft.LeadershipTransferFailedException;
93 import org.opendaylight.controller.cluster.raft.RaftActor;
94 import org.opendaylight.controller.cluster.raft.RaftActorRecoveryCohort;
95 import org.opendaylight.controller.cluster.raft.RaftActorSnapshotCohort;
96 import org.opendaylight.controller.cluster.raft.RaftState;
97 import org.opendaylight.controller.cluster.raft.base.messages.FollowerInitialSyncUpStatus;
98 import org.opendaylight.controller.cluster.raft.client.messages.OnDemandRaftState;
99 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
100 import org.opendaylight.controller.cluster.raft.messages.RequestLeadership;
101 import org.opendaylight.controller.cluster.raft.messages.ServerRemoved;
102 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
103 import org.opendaylight.yangtools.concepts.Identifier;
104 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTree;
105 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataValidationFailedException;
106 import org.opendaylight.yangtools.yang.data.api.schema.tree.TreeType;
107 import org.opendaylight.yangtools.yang.model.api.SchemaContext;
108 import org.opendaylight.yangtools.yang.model.api.SchemaContextProvider;
109 import scala.concurrent.duration.FiniteDuration;
110
111 /**
112  * A Shard represents a portion of the logical data tree.
113  *
114  * <p>
115  * Our Shard uses InMemoryDataTree as it's internal representation and delegates all requests it
116  */
117 public class Shard extends RaftActor {
118
119     @VisibleForTesting
120     static final Object TX_COMMIT_TIMEOUT_CHECK_MESSAGE = new Object() {
121         @Override
122         public String toString() {
123             return "txCommitTimeoutCheck";
124         }
125     };
126
127     @VisibleForTesting
128     static final Object GET_SHARD_MBEAN_MESSAGE = new Object() {
129         @Override
130         public String toString() {
131             return "getShardMBeanMessage";
132         }
133     };
134
135     static final Object RESUME_NEXT_PENDING_TRANSACTION = new Object() {
136         @Override
137         public String toString() {
138             return "resumeNextPendingTransaction";
139         }
140     };
141
142     // FIXME: shard names should be encapsulated in their own class and this should be exposed as a constant.
143     public static final String DEFAULT_NAME = "default";
144
145     private static final Collection<ABIVersion> SUPPORTED_ABIVERSIONS;
146
147     static {
148         final ABIVersion[] values = ABIVersion.values();
149         final ABIVersion[] real = Arrays.copyOfRange(values, 1, values.length - 1);
150         SUPPORTED_ABIVERSIONS = ImmutableList.copyOf(real).reverse();
151     }
152
153     // FIXME: make this a dynamic property based on mailbox size and maximum number of clients
154     private static final int CLIENT_MAX_MESSAGES = 1000;
155
156     // The state of this Shard
157     private final ShardDataTree store;
158
159     /// The name of this shard
160     private final String name;
161
162     private final String shardName;
163
164     private final ShardStats shardMBean;
165
166     private final ShardDataTreeListenerInfoMXBeanImpl listenerInfoMXBean;
167
168     private DatastoreContext datastoreContext;
169
170     private final ShardCommitCoordinator commitCoordinator;
171
172     private long transactionCommitTimeout;
173
174     private Cancellable txCommitTimeoutCheckSchedule;
175
176     private final Optional<ActorRef> roleChangeNotifier;
177
178     private final MessageTracker appendEntriesReplyTracker;
179
180     private final ShardTransactionActorFactory transactionActorFactory;
181
182     private final ShardSnapshotCohort snapshotCohort;
183
184     private final DataTreeChangeListenerSupport treeChangeSupport = new DataTreeChangeListenerSupport(this);
185
186     private ShardSnapshot restoreFromSnapshot;
187
188     private final ShardTransactionMessageRetrySupport messageRetrySupport;
189
190     private final FrontendMetadata frontendMetadata;
191     private Map<FrontendIdentifier, LeaderFrontendState> knownFrontends = ImmutableMap.of();
192     private boolean paused;
193
194     private final MessageSlicer responseMessageSlicer;
195     private final Dispatchers dispatchers;
196
197     private final MessageAssembler requestMessageAssembler;
198
199     protected Shard(final AbstractBuilder<?, ?> builder) {
200         super(builder.getId().toString(), builder.getPeerAddresses(),
201                 Optional.of(builder.getDatastoreContext().getShardRaftConfig()), DataStoreVersions.CURRENT_VERSION);
202
203         this.name = builder.getId().toString();
204         this.shardName = builder.getId().getShardName();
205         this.datastoreContext = builder.getDatastoreContext();
206         this.restoreFromSnapshot = builder.getRestoreFromSnapshot();
207         this.frontendMetadata = new FrontendMetadata(name);
208
209         setPersistence(datastoreContext.isPersistent());
210
211         LOG.info("Shard created : {}, persistent : {}", name, datastoreContext.isPersistent());
212
213         ShardDataTreeChangeListenerPublisherActorProxy treeChangeListenerPublisher =
214                 new ShardDataTreeChangeListenerPublisherActorProxy(getContext(), name + "-DTCL-publisher", name);
215         if (builder.getDataTree() != null) {
216             store = new ShardDataTree(this, builder.getSchemaContext(), builder.getDataTree(),
217                     treeChangeListenerPublisher, name, frontendMetadata);
218         } else {
219             store = new ShardDataTree(this, builder.getSchemaContext(), builder.getTreeType(),
220                     builder.getDatastoreContext().getStoreRoot(), treeChangeListenerPublisher, name, frontendMetadata);
221         }
222
223         shardMBean = ShardMBeanFactory.getShardStatsMBean(name, datastoreContext.getDataStoreMXBeanType(), this);
224
225         if (isMetricsCaptureEnabled()) {
226             getContext().become(new MeteringBehavior(this));
227         }
228
229         commitCoordinator = new ShardCommitCoordinator(store, LOG, this.name);
230
231         setTransactionCommitTimeout();
232
233         // create a notifier actor for each cluster member
234         roleChangeNotifier = createRoleChangeNotifier(name);
235
236         appendEntriesReplyTracker = new MessageTracker(AppendEntriesReply.class,
237                 getRaftActorContext().getConfigParams().getIsolatedCheckIntervalInMillis());
238
239         dispatchers = new Dispatchers(context().system().dispatchers());
240         transactionActorFactory = new ShardTransactionActorFactory(store, datastoreContext,
241             dispatchers.getDispatcherPath(Dispatchers.DispatcherType.Transaction),
242                 self(), getContext(), shardMBean, builder.getId().getShardName());
243
244         snapshotCohort = ShardSnapshotCohort.create(getContext(), builder.getId().getMemberName(), store, LOG,
245             this.name);
246
247         messageRetrySupport = new ShardTransactionMessageRetrySupport(this);
248
249         responseMessageSlicer = MessageSlicer.builder().logContext(this.name)
250                 .messageSliceSize(datastoreContext.getMaximumMessageSliceSize())
251                 .fileBackedStreamFactory(getRaftActorContext().getFileBackedOutputStreamFactory())
252                 .expireStateAfterInactivity(2, TimeUnit.MINUTES).build();
253
254         requestMessageAssembler = MessageAssembler.builder().logContext(this.name)
255                 .fileBackedStreamFactory(getRaftActorContext().getFileBackedOutputStreamFactory())
256                 .assembledMessageCallback((message, sender) -> self().tell(message, sender))
257                 .expireStateAfterInactivity(datastoreContext.getRequestTimeout(), TimeUnit.NANOSECONDS).build();
258
259         listenerInfoMXBean = new ShardDataTreeListenerInfoMXBeanImpl(name, datastoreContext.getDataStoreMXBeanType(),
260                 self());
261         listenerInfoMXBean.register();
262     }
263
264     private void setTransactionCommitTimeout() {
265         transactionCommitTimeout = TimeUnit.MILLISECONDS.convert(
266                 datastoreContext.getShardTransactionCommitTimeoutInSeconds(), TimeUnit.SECONDS) / 2;
267     }
268
269     private Optional<ActorRef> createRoleChangeNotifier(final String shardId) {
270         ActorRef shardRoleChangeNotifier = this.getContext().actorOf(
271             RoleChangeNotifier.getProps(shardId), shardId + "-notifier");
272         return Optional.of(shardRoleChangeNotifier);
273     }
274
275     @Override
276     public void postStop() {
277         LOG.info("Stopping Shard {}", persistenceId());
278
279         super.postStop();
280
281         messageRetrySupport.close();
282
283         if (txCommitTimeoutCheckSchedule != null) {
284             txCommitTimeoutCheckSchedule.cancel();
285         }
286
287         commitCoordinator.abortPendingTransactions("Transaction aborted due to shutdown.", this);
288
289         shardMBean.unregisterMBean();
290         listenerInfoMXBean.unregister();
291     }
292
293     @Override
294     protected void handleRecover(final Object message) {
295         LOG.debug("{}: onReceiveRecover: Received message {} from {}", persistenceId(), message.getClass(),
296             getSender());
297
298         super.handleRecover(message);
299         if (LOG.isTraceEnabled()) {
300             appendEntriesReplyTracker.begin();
301         }
302     }
303
304     @Override
305     protected void handleNonRaftCommand(final Object message) {
306         try (MessageTracker.Context context = appendEntriesReplyTracker.received(message)) {
307             final Optional<Error> maybeError = context.error();
308             if (maybeError.isPresent()) {
309                 LOG.trace("{} : AppendEntriesReply failed to arrive at the expected interval {}", persistenceId(),
310                     maybeError.get());
311             }
312
313             store.resetTransactionBatch();
314
315             if (message instanceof RequestEnvelope) {
316                 handleRequestEnvelope((RequestEnvelope)message);
317             } else if (MessageAssembler.isHandledMessage(message)) {
318                 handleRequestAssemblerMessage(message);
319             } else if (message instanceof ConnectClientRequest) {
320                 handleConnectClient((ConnectClientRequest)message);
321             } else if (CreateTransaction.isSerializedType(message)) {
322                 handleCreateTransaction(message);
323             } else if (message instanceof BatchedModifications) {
324                 handleBatchedModifications((BatchedModifications)message);
325             } else if (message instanceof ForwardedReadyTransaction) {
326                 handleForwardedReadyTransaction((ForwardedReadyTransaction) message);
327             } else if (message instanceof ReadyLocalTransaction) {
328                 handleReadyLocalTransaction((ReadyLocalTransaction)message);
329             } else if (CanCommitTransaction.isSerializedType(message)) {
330                 handleCanCommitTransaction(CanCommitTransaction.fromSerializable(message));
331             } else if (CommitTransaction.isSerializedType(message)) {
332                 handleCommitTransaction(CommitTransaction.fromSerializable(message));
333             } else if (AbortTransaction.isSerializedType(message)) {
334                 handleAbortTransaction(AbortTransaction.fromSerializable(message));
335             } else if (CloseTransactionChain.isSerializedType(message)) {
336                 closeTransactionChain(CloseTransactionChain.fromSerializable(message));
337             } else if (message instanceof RegisterDataTreeChangeListener) {
338                 treeChangeSupport.onMessage((RegisterDataTreeChangeListener) message, isLeader(), hasLeader());
339             } else if (message instanceof UpdateSchemaContext) {
340                 updateSchemaContext((UpdateSchemaContext) message);
341             } else if (message instanceof PeerAddressResolved) {
342                 PeerAddressResolved resolved = (PeerAddressResolved) message;
343                 setPeerAddress(resolved.getPeerId(), resolved.getPeerAddress());
344             } else if (TX_COMMIT_TIMEOUT_CHECK_MESSAGE.equals(message)) {
345                 commitTimeoutCheck();
346             } else if (message instanceof DatastoreContext) {
347                 onDatastoreContext((DatastoreContext)message);
348             } else if (message instanceof RegisterRoleChangeListener) {
349                 roleChangeNotifier.get().forward(message, context());
350             } else if (message instanceof FollowerInitialSyncUpStatus) {
351                 shardMBean.setFollowerInitialSyncStatus(((FollowerInitialSyncUpStatus) message).isInitialSyncDone());
352                 context().parent().tell(message, self());
353             } else if (GET_SHARD_MBEAN_MESSAGE.equals(message)) {
354                 sender().tell(getShardMBean(), self());
355             } else if (message instanceof GetShardDataTree) {
356                 sender().tell(store.getDataTree(), self());
357             } else if (message instanceof ServerRemoved) {
358                 context().parent().forward(message, context());
359             } else if (ShardTransactionMessageRetrySupport.TIMER_MESSAGE_CLASS.isInstance(message)) {
360                 messageRetrySupport.onTimerMessage(message);
361             } else if (message instanceof DataTreeCohortActorRegistry.CohortRegistryCommand) {
362                 store.processCohortRegistryCommand(getSender(),
363                         (DataTreeCohortActorRegistry.CohortRegistryCommand) message);
364             } else if (message instanceof PersistAbortTransactionPayload) {
365                 final TransactionIdentifier txId = ((PersistAbortTransactionPayload) message).getTransactionId();
366                 persistPayload(txId, AbortTransactionPayload.create(txId), true);
367             } else if (message instanceof MakeLeaderLocal) {
368                 onMakeLeaderLocal();
369             } else if (RESUME_NEXT_PENDING_TRANSACTION.equals(message)) {
370                 store.resumeNextPendingTransaction();
371             } else if (!responseMessageSlicer.handleMessage(message)) {
372                 super.handleNonRaftCommand(message);
373             }
374         }
375     }
376
377     private void handleRequestAssemblerMessage(final Object message) {
378         dispatchers.getDispatcher(DispatcherType.Serialization).execute(() -> {
379             JavaSerializer.currentSystem().value_$eq((ExtendedActorSystem) context().system());
380             requestMessageAssembler.handleMessage(message, self());
381         });
382     }
383
384     @SuppressWarnings("checkstyle:IllegalCatch")
385     private void handleRequestEnvelope(final RequestEnvelope envelope) {
386         final long now = ticker().read();
387         try {
388             final RequestSuccess<?, ?> success = handleRequest(envelope, now);
389             if (success != null) {
390                 final long executionTimeNanos = ticker().read() - now;
391                 if (success instanceof SliceableMessage) {
392                     dispatchers.getDispatcher(DispatcherType.Serialization).execute(() ->
393                         responseMessageSlicer.slice(SliceOptions.builder().identifier(success.getTarget())
394                             .message(envelope.newSuccessEnvelope(success, executionTimeNanos))
395                             .sendTo(envelope.getMessage().getReplyTo()).replyTo(self())
396                             .onFailureCallback(t -> LOG.warn("Error slicing response {}", success, t)).build()));
397                 } else {
398                     envelope.sendSuccess(success, executionTimeNanos);
399                 }
400             }
401         } catch (RequestException e) {
402             LOG.debug("{}: request {} failed", persistenceId(), envelope, e);
403             envelope.sendFailure(e, ticker().read() - now);
404         } catch (Exception e) {
405             LOG.debug("{}: request {} caused failure", persistenceId(), envelope, e);
406             envelope.sendFailure(new RuntimeRequestException("Request failed to process", e),
407                 ticker().read() - now);
408         }
409     }
410
411     private void commitTimeoutCheck() {
412         store.checkForExpiredTransactions(transactionCommitTimeout, this::updateAccess);
413         commitCoordinator.checkForExpiredTransactions(transactionCommitTimeout, this);
414         requestMessageAssembler.checkExpiredAssembledMessageState();
415     }
416
417     private Optional<Long> updateAccess(final SimpleShardDataTreeCohort cohort) {
418         final FrontendIdentifier frontend = cohort.getIdentifier().getHistoryId().getClientId().getFrontendId();
419         final LeaderFrontendState state = knownFrontends.get(frontend);
420         if (state == null) {
421             // Not tell-based protocol, do nothing
422             return Optional.absent();
423         }
424
425         if (isIsolatedLeader()) {
426             // We are isolated and no new request can come through until we emerge from it. We are still updating
427             // liveness of frontend when we see it attempting to communicate. Use the last access timer.
428             return Optional.of(state.getLastSeenTicks());
429         }
430
431         // If this frontend has freshly connected, give it some time to catch up before killing its transactions.
432         return Optional.of(state.getLastConnectTicks());
433     }
434
435     private void onMakeLeaderLocal() {
436         LOG.debug("{}: onMakeLeaderLocal received", persistenceId());
437         if (isLeader()) {
438             getSender().tell(new Status.Success(null), getSelf());
439             return;
440         }
441
442         final ActorSelection leader = getLeader();
443
444         if (leader == null) {
445             // Leader is not present. The cluster is most likely trying to
446             // elect a leader and we should let that run its normal course
447
448             // TODO we can wait for the election to complete and retry the
449             // request. We can also let the caller retry by sending a flag
450             // in the response indicating the request is "reTryable".
451             getSender().tell(new Failure(
452                     new LeadershipTransferFailedException("We cannot initiate leadership transfer to local node. "
453                             + "Currently there is no leader for " + persistenceId())),
454                     getSelf());
455             return;
456         }
457
458         leader.tell(new RequestLeadership(getId(), getSender()), getSelf());
459     }
460
461     // Acquire our frontend tracking handle and verify generation matches
462     @Nullable
463     private LeaderFrontendState findFrontend(final ClientIdentifier clientId) throws RequestException {
464         final LeaderFrontendState existing = knownFrontends.get(clientId.getFrontendId());
465         if (existing != null) {
466             final int cmp = Long.compareUnsigned(existing.getIdentifier().getGeneration(), clientId.getGeneration());
467             if (cmp == 0) {
468                 existing.touch();
469                 return existing;
470             }
471             if (cmp > 0) {
472                 LOG.debug("{}: rejecting request from outdated client {}", persistenceId(), clientId);
473                 throw new RetiredGenerationException(clientId.getGeneration(),
474                     existing.getIdentifier().getGeneration());
475             }
476
477             LOG.info("{}: retiring state {}, outdated by request from client {}", persistenceId(), existing, clientId);
478             existing.retire();
479             knownFrontends.remove(clientId.getFrontendId());
480         } else {
481             LOG.debug("{}: client {} is not yet known", persistenceId(), clientId);
482         }
483
484         return null;
485     }
486
487     private LeaderFrontendState getFrontend(final ClientIdentifier clientId) throws RequestException {
488         final LeaderFrontendState ret = findFrontend(clientId);
489         if (ret != null) {
490             return ret;
491         }
492
493         // TODO: a dedicated exception would be better, but this is technically true, too
494         throw new OutOfSequenceEnvelopeException(0);
495     }
496
497     @Nonnull
498     private static ABIVersion selectVersion(final ConnectClientRequest message) {
499         final Range<ABIVersion> clientRange = Range.closed(message.getMinVersion(), message.getMaxVersion());
500         for (ABIVersion v : SUPPORTED_ABIVERSIONS) {
501             if (clientRange.contains(v)) {
502                 return v;
503             }
504         }
505
506         throw new IllegalArgumentException(String.format(
507             "No common version between backend versions %s and client versions %s", SUPPORTED_ABIVERSIONS,
508             clientRange));
509     }
510
511     @SuppressWarnings("checkstyle:IllegalCatch")
512     private void handleConnectClient(final ConnectClientRequest message) {
513         try {
514             final ClientIdentifier clientId = message.getTarget();
515             final LeaderFrontendState existing = findFrontend(clientId);
516             if (existing != null) {
517                 existing.touch();
518             }
519
520             if (!isLeader() || !isLeaderActive()) {
521                 LOG.info("{}: not currently leader, rejecting request {}. isLeader: {}, isLeaderActive: {},"
522                                 + "isLeadershipTransferInProgress: {}.",
523                         persistenceId(), message, isLeader(), isLeaderActive(), isLeadershipTransferInProgress());
524                 throw new NotLeaderException(getSelf());
525             }
526
527             final ABIVersion selectedVersion = selectVersion(message);
528             final LeaderFrontendState frontend;
529             if (existing == null) {
530                 frontend = new LeaderFrontendState(persistenceId(), clientId, store);
531                 knownFrontends.put(clientId.getFrontendId(), frontend);
532                 LOG.debug("{}: created state {} for client {}", persistenceId(), frontend, clientId);
533             } else {
534                 frontend = existing;
535             }
536
537             frontend.reconnect();
538             message.getReplyTo().tell(new ConnectClientSuccess(message.getTarget(), message.getSequence(), getSelf(),
539                 ImmutableList.of(), store.getDataTree(), CLIENT_MAX_MESSAGES).toVersion(selectedVersion),
540                 ActorRef.noSender());
541         } catch (RequestException | RuntimeException e) {
542             message.getReplyTo().tell(new Failure(e), ActorRef.noSender());
543         }
544     }
545
546     @Nullable
547     private RequestSuccess<?, ?> handleRequest(final RequestEnvelope envelope, final long now)
548             throws RequestException {
549         // We are not the leader, hence we want to fail-fast.
550         if (!isLeader() || paused || !isLeaderActive()) {
551             LOG.debug("{}: not currently active leader, rejecting request {}. isLeader: {}, isLeaderActive: {},"
552                             + "isLeadershipTransferInProgress: {}, paused: {}",
553                     persistenceId(), envelope, isLeader(), isLeaderActive(), isLeadershipTransferInProgress(), paused);
554             throw new NotLeaderException(getSelf());
555         }
556
557         final Request<?, ?> request = envelope.getMessage();
558         if (request instanceof TransactionRequest) {
559             final TransactionRequest<?> txReq = (TransactionRequest<?>)request;
560             final ClientIdentifier clientId = txReq.getTarget().getHistoryId().getClientId();
561             return getFrontend(clientId).handleTransactionRequest(txReq, envelope, now);
562         } else if (request instanceof LocalHistoryRequest) {
563             final LocalHistoryRequest<?> lhReq = (LocalHistoryRequest<?>)request;
564             final ClientIdentifier clientId = lhReq.getTarget().getClientId();
565             return getFrontend(clientId).handleLocalHistoryRequest(lhReq, envelope, now);
566         } else {
567             LOG.warn("{}: rejecting unsupported request {}", persistenceId(), request);
568             throw new UnsupportedRequestException(request);
569         }
570     }
571
572     private boolean hasLeader() {
573         return getLeaderId() != null;
574     }
575
576     public int getPendingTxCommitQueueSize() {
577         return store.getQueueSize();
578     }
579
580     public int getCohortCacheSize() {
581         return commitCoordinator.getCohortCacheSize();
582     }
583
584     @Override
585     protected Optional<ActorRef> getRoleChangeNotifier() {
586         return roleChangeNotifier;
587     }
588
589     String getShardName() {
590         return shardName;
591     }
592
593     @Override
594     protected LeaderStateChanged newLeaderStateChanged(final String memberId, final String leaderId,
595             final short leaderPayloadVersion) {
596         return isLeader() ? new ShardLeaderStateChanged(memberId, leaderId, store.getDataTree(), leaderPayloadVersion)
597                 : new ShardLeaderStateChanged(memberId, leaderId, leaderPayloadVersion);
598     }
599
600     protected void onDatastoreContext(final DatastoreContext context) {
601         datastoreContext = context;
602
603         setTransactionCommitTimeout();
604
605         setPersistence(datastoreContext.isPersistent());
606
607         updateConfigParams(datastoreContext.getShardRaftConfig());
608     }
609
610     // applyState() will be invoked once consensus is reached on the payload
611     void persistPayload(final Identifier id, final Payload payload, final boolean batchHint) {
612         boolean canSkipPayload = !hasFollowers() && !persistence().isRecoveryApplicable();
613         if (canSkipPayload) {
614             applyState(self(), id, payload);
615         } else {
616             // We are faking the sender
617             persistData(self(), id, payload, batchHint);
618         }
619     }
620
621     private void handleCommitTransaction(final CommitTransaction commit) {
622         if (isLeader()) {
623             commitCoordinator.handleCommit(commit.getTransactionId(), getSender(), this);
624         } else {
625             ActorSelection leader = getLeader();
626             if (leader == null) {
627                 messageRetrySupport.addMessageToRetry(commit, getSender(),
628                         "Could not commit transaction " + commit.getTransactionId());
629             } else {
630                 LOG.debug("{}: Forwarding CommitTransaction to leader {}", persistenceId(), leader);
631                 leader.forward(commit, getContext());
632             }
633         }
634     }
635
636     private void handleCanCommitTransaction(final CanCommitTransaction canCommit) {
637         LOG.debug("{}: Can committing transaction {}", persistenceId(), canCommit.getTransactionId());
638
639         if (isLeader()) {
640             commitCoordinator.handleCanCommit(canCommit.getTransactionId(), getSender(), this);
641         } else {
642             ActorSelection leader = getLeader();
643             if (leader == null) {
644                 messageRetrySupport.addMessageToRetry(canCommit, getSender(),
645                         "Could not canCommit transaction " + canCommit.getTransactionId());
646             } else {
647                 LOG.debug("{}: Forwarding CanCommitTransaction to leader {}", persistenceId(), leader);
648                 leader.forward(canCommit, getContext());
649             }
650         }
651     }
652
653     @SuppressWarnings("checkstyle:IllegalCatch")
654     protected void handleBatchedModificationsLocal(final BatchedModifications batched, final ActorRef sender) {
655         try {
656             commitCoordinator.handleBatchedModifications(batched, sender, this);
657         } catch (Exception e) {
658             LOG.error("{}: Error handling BatchedModifications for Tx {}", persistenceId(),
659                     batched.getTransactionId(), e);
660             sender.tell(new Failure(e), getSelf());
661         }
662     }
663
664     private void handleBatchedModifications(final BatchedModifications batched) {
665         // This message is sent to prepare the modifications transaction directly on the Shard as an
666         // optimization to avoid the extra overhead of a separate ShardTransaction actor. On the last
667         // BatchedModifications message, the caller sets the ready flag in the message indicating
668         // modifications are complete. The reply contains the cohort actor path (this actor) for the caller
669         // to initiate the 3-phase commit. This also avoids the overhead of sending an additional
670         // ReadyTransaction message.
671
672         // If we're not the leader then forward to the leader. This is a safety measure - we shouldn't
673         // normally get here if we're not the leader as the front-end (TransactionProxy) should determine
674         // the primary/leader shard. However with timing and caching on the front-end, there's a small
675         // window where it could have a stale leader during leadership transitions.
676         //
677         boolean isLeaderActive = isLeaderActive();
678         if (isLeader() && isLeaderActive) {
679             handleBatchedModificationsLocal(batched, getSender());
680         } else {
681             ActorSelection leader = getLeader();
682             if (!isLeaderActive || leader == null) {
683                 messageRetrySupport.addMessageToRetry(batched, getSender(),
684                         "Could not process BatchedModifications " + batched.getTransactionId());
685             } else {
686                 // If this is not the first batch and leadership changed in between batched messages,
687                 // we need to reconstruct previous BatchedModifications from the transaction
688                 // DataTreeModification, honoring the max batched modification count, and forward all the
689                 // previous BatchedModifications to the new leader.
690                 Collection<BatchedModifications> newModifications = commitCoordinator
691                         .createForwardedBatchedModifications(batched,
692                                 datastoreContext.getShardBatchedModificationCount());
693
694                 LOG.debug("{}: Forwarding {} BatchedModifications to leader {}", persistenceId(),
695                         newModifications.size(), leader);
696
697                 for (BatchedModifications bm : newModifications) {
698                     leader.forward(bm, getContext());
699                 }
700             }
701         }
702     }
703
704     private boolean failIfIsolatedLeader(final ActorRef sender) {
705         if (isIsolatedLeader()) {
706             sender.tell(new Failure(new NoShardLeaderException(String.format(
707                     "Shard %s was the leader but has lost contact with all of its followers. Either all"
708                     + " other follower nodes are down or this node is isolated by a network partition.",
709                     persistenceId()))), getSelf());
710             return true;
711         }
712
713         return false;
714     }
715
716     protected boolean isIsolatedLeader() {
717         return getRaftState() == RaftState.IsolatedLeader;
718     }
719
720     @SuppressWarnings("checkstyle:IllegalCatch")
721     private void handleReadyLocalTransaction(final ReadyLocalTransaction message) {
722         LOG.debug("{}: handleReadyLocalTransaction for {}", persistenceId(), message.getTransactionId());
723
724         boolean isLeaderActive = isLeaderActive();
725         if (isLeader() && isLeaderActive) {
726             try {
727                 commitCoordinator.handleReadyLocalTransaction(message, getSender(), this);
728             } catch (Exception e) {
729                 LOG.error("{}: Error handling ReadyLocalTransaction for Tx {}", persistenceId(),
730                         message.getTransactionId(), e);
731                 getSender().tell(new Failure(e), getSelf());
732             }
733         } else {
734             ActorSelection leader = getLeader();
735             if (!isLeaderActive || leader == null) {
736                 messageRetrySupport.addMessageToRetry(message, getSender(),
737                         "Could not process ready local transaction " + message.getTransactionId());
738             } else {
739                 LOG.debug("{}: Forwarding ReadyLocalTransaction to leader {}", persistenceId(), leader);
740                 message.setRemoteVersion(getCurrentBehavior().getLeaderPayloadVersion());
741                 leader.forward(message, getContext());
742             }
743         }
744     }
745
746     private void handleForwardedReadyTransaction(final ForwardedReadyTransaction forwardedReady) {
747         LOG.debug("{}: handleForwardedReadyTransaction for {}", persistenceId(), forwardedReady.getTransactionId());
748
749         boolean isLeaderActive = isLeaderActive();
750         if (isLeader() && isLeaderActive) {
751             commitCoordinator.handleForwardedReadyTransaction(forwardedReady, getSender(), this);
752         } else {
753             ActorSelection leader = getLeader();
754             if (!isLeaderActive || leader == null) {
755                 messageRetrySupport.addMessageToRetry(forwardedReady, getSender(),
756                         "Could not process forwarded ready transaction " + forwardedReady.getTransactionId());
757             } else {
758                 LOG.debug("{}: Forwarding ForwardedReadyTransaction to leader {}", persistenceId(), leader);
759
760                 ReadyLocalTransaction readyLocal = new ReadyLocalTransaction(forwardedReady.getTransactionId(),
761                         forwardedReady.getTransaction().getSnapshot(), forwardedReady.isDoImmediateCommit(),
762                         forwardedReady.getParticipatingShardNames());
763                 readyLocal.setRemoteVersion(getCurrentBehavior().getLeaderPayloadVersion());
764                 leader.forward(readyLocal, getContext());
765             }
766         }
767     }
768
769     private void handleAbortTransaction(final AbortTransaction abort) {
770         doAbortTransaction(abort.getTransactionId(), getSender());
771     }
772
773     void doAbortTransaction(final Identifier transactionID, final ActorRef sender) {
774         commitCoordinator.handleAbort(transactionID, sender, this);
775     }
776
777     private void handleCreateTransaction(final Object message) {
778         if (isLeader()) {
779             createTransaction(CreateTransaction.fromSerializable(message));
780         } else if (getLeader() != null) {
781             getLeader().forward(message, getContext());
782         } else {
783             getSender().tell(new Failure(new NoShardLeaderException(
784                     "Could not create a shard transaction", persistenceId())), getSelf());
785         }
786     }
787
788     private void closeTransactionChain(final CloseTransactionChain closeTransactionChain) {
789         if (isLeader()) {
790             final LocalHistoryIdentifier id = closeTransactionChain.getIdentifier();
791             // FIXME: CONTROLLER-1628: stage purge once no transactions are present
792             store.closeTransactionChain(id, null);
793             store.purgeTransactionChain(id, null);
794         } else if (getLeader() != null) {
795             getLeader().forward(closeTransactionChain, getContext());
796         } else {
797             LOG.warn("{}: Could not close transaction {}", persistenceId(), closeTransactionChain.getIdentifier());
798         }
799     }
800
801     @SuppressWarnings("checkstyle:IllegalCatch")
802     private void createTransaction(final CreateTransaction createTransaction) {
803         try {
804             if (TransactionType.fromInt(createTransaction.getTransactionType()) != TransactionType.READ_ONLY
805                     && failIfIsolatedLeader(getSender())) {
806                 return;
807             }
808
809             ActorRef transactionActor = createTransaction(createTransaction.getTransactionType(),
810                 createTransaction.getTransactionId());
811
812             getSender().tell(new CreateTransactionReply(Serialization.serializedActorPath(transactionActor),
813                     createTransaction.getTransactionId(), createTransaction.getVersion()).toSerializable(), getSelf());
814         } catch (Exception e) {
815             getSender().tell(new Failure(e), getSelf());
816         }
817     }
818
819     private ActorRef createTransaction(final int transactionType, final TransactionIdentifier transactionId) {
820         LOG.debug("{}: Creating transaction : {} ", persistenceId(), transactionId);
821         return transactionActorFactory.newShardTransaction(TransactionType.fromInt(transactionType),
822             transactionId);
823     }
824
825     private void updateSchemaContext(final UpdateSchemaContext message) {
826         updateSchemaContext(message.getSchemaContext());
827     }
828
829     @VisibleForTesting
830     void updateSchemaContext(final SchemaContext schemaContext) {
831         store.updateSchemaContext(schemaContext);
832     }
833
834     private boolean isMetricsCaptureEnabled() {
835         CommonConfig config = new CommonConfig(getContext().system().settings().config());
836         return config.isMetricCaptureEnabled();
837     }
838
839     @Override
840     @VisibleForTesting
841     public RaftActorSnapshotCohort getRaftActorSnapshotCohort() {
842         return snapshotCohort;
843     }
844
845     @Override
846     @Nonnull
847     protected RaftActorRecoveryCohort getRaftActorRecoveryCohort() {
848         if (restoreFromSnapshot == null) {
849             return ShardRecoveryCoordinator.create(store, persistenceId(), LOG);
850         }
851
852         return ShardRecoveryCoordinator.forSnapshot(store, persistenceId(), LOG, restoreFromSnapshot.getSnapshot());
853     }
854
855     @Override
856     protected void onRecoveryComplete() {
857         restoreFromSnapshot = null;
858
859         //notify shard manager
860         getContext().parent().tell(new ActorInitialized(), getSelf());
861
862         // Being paranoid here - this method should only be called once but just in case...
863         if (txCommitTimeoutCheckSchedule == null) {
864             // Schedule a message to be periodically sent to check if the current in-progress
865             // transaction should be expired and aborted.
866             FiniteDuration period = FiniteDuration.create(transactionCommitTimeout / 3, TimeUnit.MILLISECONDS);
867             txCommitTimeoutCheckSchedule = getContext().system().scheduler().schedule(
868                     period, period, getSelf(),
869                     TX_COMMIT_TIMEOUT_CHECK_MESSAGE, getContext().dispatcher(), ActorRef.noSender());
870         }
871     }
872
873     @Override
874     protected void applyState(final ActorRef clientActor, final Identifier identifier, final Object data) {
875         if (data instanceof Payload) {
876             try {
877                 store.applyReplicatedPayload(identifier, (Payload)data);
878             } catch (DataValidationFailedException | IOException e) {
879                 LOG.error("{}: Error applying replica {}", persistenceId(), identifier, e);
880             }
881         } else {
882             LOG.error("{}: Unknown state for {} received {}", persistenceId(), identifier, data);
883         }
884     }
885
886     @Override
887     protected void onStateChanged() {
888         boolean isLeader = isLeader();
889         boolean hasLeader = hasLeader();
890         treeChangeSupport.onLeadershipChange(isLeader, hasLeader);
891
892         // If this actor is no longer the leader close all the transaction chains
893         if (!isLeader) {
894             if (LOG.isDebugEnabled()) {
895                 LOG.debug(
896                     "{}: onStateChanged: Closing all transaction chains because shard {} is no longer the leader",
897                     persistenceId(), getId());
898             }
899
900             paused = false;
901             store.purgeLeaderState();
902         }
903
904         if (hasLeader && !isIsolatedLeader()) {
905             messageRetrySupport.retryMessages();
906         }
907     }
908
909     @Override
910     protected void onLeaderChanged(final String oldLeader, final String newLeader) {
911         shardMBean.incrementLeadershipChangeCount();
912         paused = false;
913
914         if (!isLeader()) {
915             if (!knownFrontends.isEmpty()) {
916                 LOG.debug("{}: removing frontend state for {}", persistenceId(), knownFrontends.keySet());
917                 knownFrontends = ImmutableMap.of();
918             }
919
920             requestMessageAssembler.close();
921
922             if (!hasLeader()) {
923                 // No leader anywhere, nothing else to do
924                 return;
925             }
926
927             // Another leader was elected. If we were the previous leader and had pending transactions, convert
928             // them to transaction messages and send to the new leader.
929             ActorSelection leader = getLeader();
930             if (leader != null) {
931                 Collection<?> messagesToForward = convertPendingTransactionsToMessages();
932
933                 if (!messagesToForward.isEmpty()) {
934                     LOG.debug("{}: Forwarding {} pending transaction messages to leader {}", persistenceId(),
935                             messagesToForward.size(), leader);
936
937                     for (Object message : messagesToForward) {
938                         LOG.debug("{}: Forwarding pending transaction message {}", persistenceId(), message);
939
940                         leader.tell(message, self());
941                     }
942                 }
943             } else {
944                 commitCoordinator.abortPendingTransactions("The transacton was aborted due to inflight leadership "
945                         + "change and the leader address isn't available.", this);
946             }
947         } else {
948             // We have become the leader, we need to reconstruct frontend state
949             knownFrontends = Verify.verifyNotNull(frontendMetadata.toLeaderState(this));
950             LOG.debug("{}: became leader with frontend state for {}", persistenceId(), knownFrontends.keySet());
951         }
952
953         if (!isIsolatedLeader()) {
954             messageRetrySupport.retryMessages();
955         }
956     }
957
958     /**
959      * Clears all pending transactions and converts them to messages to be forwarded to a new leader.
960      *
961      * @return the converted messages
962      */
963     public Collection<?> convertPendingTransactionsToMessages() {
964         return commitCoordinator.convertPendingTransactionsToMessages(
965                 datastoreContext.getShardBatchedModificationCount());
966     }
967
968     @Override
969     protected void pauseLeader(final Runnable operation) {
970         LOG.debug("{}: In pauseLeader, operation: {}", persistenceId(), operation);
971         paused = true;
972
973         // Tell-based protocol can replay transaction state, so it is safe to blow it up when we are paused.
974         knownFrontends.values().forEach(LeaderFrontendState::retire);
975         knownFrontends = ImmutableMap.of();
976
977         store.setRunOnPendingTransactionsComplete(operation);
978     }
979
980     @Override
981     protected void unpauseLeader() {
982         LOG.debug("{}: In unpauseLeader", persistenceId());
983         paused = false;
984
985         store.setRunOnPendingTransactionsComplete(null);
986
987         // Restore tell-based protocol state as if we were becoming the leader
988         knownFrontends = Verify.verifyNotNull(frontendMetadata.toLeaderState(this));
989     }
990
991     @Override
992     protected OnDemandRaftState.AbstractBuilder<?, ?> newOnDemandRaftStateBuilder() {
993         return OnDemandShardState.newBuilder().treeChangeListenerActors(treeChangeSupport.getListenerActors())
994                 .commitCohortActors(store.getCohortActors());
995     }
996
997     @Override
998     public String persistenceId() {
999         return this.name;
1000     }
1001
1002     @VisibleForTesting
1003     ShardCommitCoordinator getCommitCoordinator() {
1004         return commitCoordinator;
1005     }
1006
1007     public DatastoreContext getDatastoreContext() {
1008         return datastoreContext;
1009     }
1010
1011     @VisibleForTesting
1012     public ShardDataTree getDataStore() {
1013         return store;
1014     }
1015
1016     @VisibleForTesting
1017     ShardStats getShardMBean() {
1018         return shardMBean;
1019     }
1020
1021     public static Builder builder() {
1022         return new Builder();
1023     }
1024
1025     public abstract static class AbstractBuilder<T extends AbstractBuilder<T, S>, S extends Shard> {
1026         private final Class<S> shardClass;
1027         private ShardIdentifier id;
1028         private Map<String, String> peerAddresses = Collections.emptyMap();
1029         private DatastoreContext datastoreContext;
1030         private SchemaContextProvider schemaContextProvider;
1031         private DatastoreSnapshot.ShardSnapshot restoreFromSnapshot;
1032         private DataTree dataTree;
1033         private volatile boolean sealed;
1034
1035         protected AbstractBuilder(final Class<S> shardClass) {
1036             this.shardClass = shardClass;
1037         }
1038
1039         protected void checkSealed() {
1040             Preconditions.checkState(!sealed, "Builder isalready sealed - further modifications are not allowed");
1041         }
1042
1043         @SuppressWarnings("unchecked")
1044         private T self() {
1045             return (T) this;
1046         }
1047
1048         public T id(final ShardIdentifier newId) {
1049             checkSealed();
1050             this.id = newId;
1051             return self();
1052         }
1053
1054         public T peerAddresses(final Map<String, String> newPeerAddresses) {
1055             checkSealed();
1056             this.peerAddresses = newPeerAddresses;
1057             return self();
1058         }
1059
1060         public T datastoreContext(final DatastoreContext newDatastoreContext) {
1061             checkSealed();
1062             this.datastoreContext = newDatastoreContext;
1063             return self();
1064         }
1065
1066         public T schemaContextProvider(final SchemaContextProvider newSchemaContextProvider) {
1067             checkSealed();
1068             this.schemaContextProvider = Preconditions.checkNotNull(newSchemaContextProvider);
1069             return self();
1070         }
1071
1072         public T restoreFromSnapshot(final DatastoreSnapshot.ShardSnapshot newRestoreFromSnapshot) {
1073             checkSealed();
1074             this.restoreFromSnapshot = newRestoreFromSnapshot;
1075             return self();
1076         }
1077
1078         public T dataTree(final DataTree newDataTree) {
1079             checkSealed();
1080             this.dataTree = newDataTree;
1081             return self();
1082         }
1083
1084         public ShardIdentifier getId() {
1085             return id;
1086         }
1087
1088         public Map<String, String> getPeerAddresses() {
1089             return peerAddresses;
1090         }
1091
1092         public DatastoreContext getDatastoreContext() {
1093             return datastoreContext;
1094         }
1095
1096         public SchemaContext getSchemaContext() {
1097             return Verify.verifyNotNull(schemaContextProvider.getSchemaContext());
1098         }
1099
1100         public DatastoreSnapshot.ShardSnapshot getRestoreFromSnapshot() {
1101             return restoreFromSnapshot;
1102         }
1103
1104         public DataTree getDataTree() {
1105             return dataTree;
1106         }
1107
1108         public TreeType getTreeType() {
1109             switch (datastoreContext.getLogicalStoreType()) {
1110                 case CONFIGURATION:
1111                     return TreeType.CONFIGURATION;
1112                 case OPERATIONAL:
1113                     return TreeType.OPERATIONAL;
1114                 default:
1115                     throw new IllegalStateException("Unhandled logical store type "
1116                             + datastoreContext.getLogicalStoreType());
1117             }
1118         }
1119
1120         protected void verify() {
1121             Preconditions.checkNotNull(id, "id should not be null");
1122             Preconditions.checkNotNull(peerAddresses, "peerAddresses should not be null");
1123             Preconditions.checkNotNull(datastoreContext, "dataStoreContext should not be null");
1124             Preconditions.checkNotNull(schemaContextProvider, "schemaContextProvider should not be null");
1125         }
1126
1127         public Props props() {
1128             sealed = true;
1129             verify();
1130             return Props.create(shardClass, this);
1131         }
1132     }
1133
1134     public static class Builder extends AbstractBuilder<Builder, Shard> {
1135         Builder() {
1136             super(Shard.class);
1137         }
1138     }
1139
1140     Ticker ticker() {
1141         return Ticker.systemTicker();
1142     }
1143
1144     void scheduleNextPendingTransaction() {
1145         self().tell(RESUME_NEXT_PENDING_TRANSACTION, ActorRef.noSender());
1146     }
1147 }

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