opendaylight/md-sal/sal-distributed-datastore/src/test/java/org/opendaylight/controller/cluster/datastore/AbstractShardTest.java

   1 /*
   2  * Copyright (c) 2015 Brocade Communications 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 static org.junit.Assert.assertEquals;
  11 import static org.junit.Assert.assertNotNull;
  12 import static org.junit.Assert.assertTrue;
  13 import static org.junit.Assert.fail;
  14 import static org.mockito.Matchers.any;
  15 import static org.mockito.Mockito.doAnswer;
  16 import static org.mockito.Mockito.doNothing;
  17 import static org.mockito.Mockito.doReturn;
  18 import static org.mockito.Mockito.mock;
  19 import static org.opendaylight.controller.cluster.datastore.DataStoreVersions.CURRENT_VERSION;
  20 import akka.actor.ActorRef;
  21 import akka.actor.PoisonPill;
  22 import akka.actor.Props;
  23 import akka.dispatch.Dispatchers;
  24 import akka.japi.Creator;
  25 import akka.pattern.Patterns;
  26 import akka.testkit.TestActorRef;
  27 import akka.util.Timeout;
  28 import com.google.common.base.Function;
  29 import com.google.common.base.Optional;
  30 import com.google.common.util.concurrent.Futures;
  31 import com.google.common.util.concurrent.ListenableFuture;
  32 import com.google.common.util.concurrent.Uninterruptibles;
  33 import java.util.Collections;
  34 import java.util.Set;
  35 import java.util.concurrent.CountDownLatch;
  36 import java.util.concurrent.ExecutionException;
  37 import java.util.concurrent.TimeUnit;
  38 import java.util.concurrent.TimeoutException;
  39 import java.util.concurrent.atomic.AtomicInteger;
  40 import org.junit.After;
  41 import org.junit.Assert;
  42 import org.junit.Before;
  43 import org.mockito.invocation.InvocationOnMock;
  44 import org.mockito.stubbing.Answer;
  45 import org.opendaylight.controller.cluster.access.concepts.MemberName;
  46 import org.opendaylight.controller.cluster.access.concepts.TransactionIdentifier;
  47 import org.opendaylight.controller.cluster.datastore.DatastoreContext.Builder;
  48 import org.opendaylight.controller.cluster.datastore.identifiers.ShardIdentifier;
  49 import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
  50 import org.opendaylight.controller.cluster.datastore.messages.ForwardedReadyTransaction;
  51 import org.opendaylight.controller.cluster.datastore.modification.MutableCompositeModification;
  52 import org.opendaylight.controller.cluster.datastore.modification.WriteModification;
  53 import org.opendaylight.controller.cluster.datastore.utils.SerializationUtils;
  54 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  55 import org.opendaylight.controller.cluster.raft.Snapshot;
  56 import org.opendaylight.controller.cluster.raft.TestActorFactory;
  57 import org.opendaylight.controller.cluster.raft.utils.InMemoryJournal;
  58 import org.opendaylight.controller.cluster.raft.utils.InMemorySnapshotStore;
  59 import org.opendaylight.controller.md.cluster.datastore.model.CarsModel;
  60 import org.opendaylight.controller.md.cluster.datastore.model.TestModel;
  61 import org.opendaylight.yangtools.concepts.Identifier;
  62 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
  63 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
  64 import org.opendaylight.yangtools.yang.data.api.schema.DataContainerChild;
  65 import org.opendaylight.yangtools.yang.data.api.schema.MapEntryNode;
  66 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
  67 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTree;
  68 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeCandidate;
  69 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeCandidateNode;
  70 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeCandidateTip;
  71 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeModification;
  72 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataValidationFailedException;
  73 import org.opendaylight.yangtools.yang.data.api.schema.tree.ModificationType;
  74 import org.opendaylight.yangtools.yang.data.api.schema.tree.TreeType;
  75 import org.opendaylight.yangtools.yang.data.impl.schema.ImmutableNodes;
  76 import org.opendaylight.yangtools.yang.data.impl.schema.tree.InMemoryDataTreeFactory;
  77 import org.opendaylight.yangtools.yang.model.api.SchemaContext;
  78 import scala.concurrent.Await;
  79 import scala.concurrent.Future;
  80 import scala.concurrent.duration.Duration;
  81
  82 /**
  83  * Abstract base for shard unit tests.
  84  *
  85  * @author Thomas Pantelis
  86  */
  87 public abstract class AbstractShardTest extends AbstractActorTest{
  88     protected static final SchemaContext SCHEMA_CONTEXT = TestModel.createTestContext();
  89
  90     private static final AtomicInteger NEXT_SHARD_NUM = new AtomicInteger();
  91
  92     protected final ShardIdentifier shardID = ShardIdentifier.create("inventory", MemberName.forName("member-1"),
  93         "config" + NEXT_SHARD_NUM.getAndIncrement());
  94
  95     protected final Builder dataStoreContextBuilder = DatastoreContext.newBuilder().
  96             shardJournalRecoveryLogBatchSize(3).shardSnapshotBatchCount(5000).
  97             shardHeartbeatIntervalInMillis(100);
  98
  99     protected final TestActorFactory actorFactory = new TestActorFactory(getSystem());
 100
 101     @Before
 102     public void setUp() {
 103         InMemorySnapshotStore.clear();
 104         InMemoryJournal.clear();
 105     }
 106
 107     @After
 108     public void tearDown() {
 109         InMemorySnapshotStore.clear();
 110         InMemoryJournal.clear();
 111         actorFactory.close();
 112     }
 113
 114     protected DatastoreContext newDatastoreContext() {
 115         return dataStoreContextBuilder.build();
 116     }
 117
 118     protected Props newShardProps() {
 119         return newShardBuilder().props();
 120     }
 121
 122     protected Shard.Builder newShardBuilder() {
 123         return Shard.builder().id(shardID).datastoreContext(newDatastoreContext()).schemaContext(SCHEMA_CONTEXT);
 124     }
 125
 126     protected void testRecovery(final Set<Integer> listEntryKeys) throws Exception {
 127         // Create the actor and wait for recovery complete.
 128
 129         final int nListEntries = listEntryKeys.size();
 130
 131         final CountDownLatch recoveryComplete = new CountDownLatch(1);
 132
 133         @SuppressWarnings("serial")
 134         final Creator<Shard> creator = new Creator<Shard>() {
 135             @Override
 136             public Shard create() throws Exception {
 137                 return new Shard(newShardBuilder()) {
 138                     @Override
 139                     protected void onRecoveryComplete() {
 140                         try {
 141                             super.onRecoveryComplete();
 142                         } finally {
 143                             recoveryComplete.countDown();
 144                         }
 145                     }
 146                 };
 147             }
 148         };
 149
 150         final TestActorRef<Shard> shard = TestActorRef.create(getSystem(),
 151                 Props.create(new DelegatingShardCreator(creator)).withDispatcher(Dispatchers.DefaultDispatcherId()), "testRecovery");
 152
 153         assertEquals("Recovery complete", true, recoveryComplete.await(5, TimeUnit.SECONDS));
 154
 155         // Verify data in the data store.
 156
 157         final NormalizedNode<?, ?> outerList = readStore(shard, TestModel.OUTER_LIST_PATH);
 158         assertNotNull(TestModel.OUTER_LIST_QNAME.getLocalName() + " not found", outerList);
 159         assertTrue(TestModel.OUTER_LIST_QNAME.getLocalName() + " value is not Iterable",
 160                 outerList.getValue() instanceof Iterable);
 161         for(final Object entry: (Iterable<?>) outerList.getValue()) {
 162             assertTrue(TestModel.OUTER_LIST_QNAME.getLocalName() + " entry is not MapEntryNode",
 163                     entry instanceof MapEntryNode);
 164             final MapEntryNode mapEntry = (MapEntryNode)entry;
 165             final Optional<DataContainerChild<? extends PathArgument, ?>> idLeaf =
 166                     mapEntry.getChild(new YangInstanceIdentifier.NodeIdentifier(TestModel.ID_QNAME));
 167             assertTrue("Missing leaf " + TestModel.ID_QNAME.getLocalName(), idLeaf.isPresent());
 168             final Object value = idLeaf.get().getValue();
 169             assertTrue("Unexpected value for leaf "+ TestModel.ID_QNAME.getLocalName() + ": " + value,
 170                     listEntryKeys.remove(value));
 171         }
 172
 173         if(!listEntryKeys.isEmpty()) {
 174             fail("Missing " + TestModel.OUTER_LIST_QNAME.getLocalName() + " entries with keys: " +
 175                     listEntryKeys);
 176         }
 177
 178         assertEquals("Last log index", nListEntries,
 179                 shard.underlyingActor().getShardMBean().getLastLogIndex());
 180         assertEquals("Commit index", nListEntries,
 181                 shard.underlyingActor().getShardMBean().getCommitIndex());
 182         assertEquals("Last applied", nListEntries,
 183                 shard.underlyingActor().getShardMBean().getLastApplied());
 184
 185         shard.tell(PoisonPill.getInstance(), ActorRef.noSender());
 186     }
 187
 188     protected void verifyLastApplied(final TestActorRef<Shard> shard, final long expectedValue) {
 189         long lastApplied = -1;
 190         for(int i = 0; i < 20 * 5; i++) {
 191             lastApplied = shard.underlyingActor().getShardMBean().getLastApplied();
 192             if(lastApplied == expectedValue) {
 193                 return;
 194             }
 195             Uninterruptibles.sleepUninterruptibly(50, TimeUnit.MILLISECONDS);
 196         }
 197
 198         Assert.fail(String.format("Expected last applied: %d, Actual: %d", expectedValue, lastApplied));
 199     }
 200
 201     protected ShardDataTreeCohort setupMockWriteTransaction(final String cohortName,
 202             final ShardDataTree dataStore, final YangInstanceIdentifier path, final NormalizedNode<?, ?> data,
 203             final MutableCompositeModification modification) {
 204         return setupMockWriteTransaction(cohortName, dataStore, path, data, modification, null);
 205     }
 206
 207     protected ShardDataTreeCohort setupMockWriteTransaction(final String cohortName,
 208             final ShardDataTree dataStore, final YangInstanceIdentifier path, final NormalizedNode<?, ?> data,
 209             final MutableCompositeModification modification,
 210             final Function<ShardDataTreeCohort, ListenableFuture<Void>> preCommit) {
 211
 212         final ReadWriteShardDataTreeTransaction tx = dataStore.newReadWriteTransaction(nextTransactionId());
 213         tx.getSnapshot().write(path, data);
 214         final ShardDataTreeCohort cohort = createDelegatingMockCohort(cohortName, dataStore.finishTransaction(tx), preCommit);
 215
 216         modification.addModification(new WriteModification(path, data));
 217
 218         return cohort;
 219     }
 220
 221     protected ShardDataTreeCohort createDelegatingMockCohort(final String cohortName,
 222             final ShardDataTreeCohort actual) {
 223         return createDelegatingMockCohort(cohortName, actual, null);
 224     }
 225
 226     protected ShardDataTreeCohort createDelegatingMockCohort(final String cohortName,
 227             final ShardDataTreeCohort actual,
 228             final Function<ShardDataTreeCohort, ListenableFuture<Void>> preCommit) {
 229         final ShardDataTreeCohort cohort = mock(ShardDataTreeCohort.class, cohortName);
 230
 231         doAnswer(new Answer<ListenableFuture<Boolean>>() {
 232             @Override
 233             public ListenableFuture<Boolean> answer(final InvocationOnMock invocation) {
 234                 return actual.canCommit();
 235             }
 236         }).when(cohort).canCommit();
 237
 238         doAnswer(new Answer<ListenableFuture<Void>>() {
 239             @Override
 240             public ListenableFuture<Void> answer(final InvocationOnMock invocation) throws Throwable {
 241                 if(preCommit != null) {
 242                     return preCommit.apply(actual);
 243                 } else {
 244                     return actual.preCommit();
 245                 }
 246             }
 247         }).when(cohort).preCommit();
 248
 249         doAnswer(new Answer<ListenableFuture<Void>>() {
 250             @Override
 251             public ListenableFuture<Void> answer(final InvocationOnMock invocation) throws Throwable {
 252                 return actual.commit();
 253             }
 254         }).when(cohort).commit();
 255
 256         doAnswer(new Answer<ListenableFuture<Void>>() {
 257             @Override
 258             public ListenableFuture<Void> answer(final InvocationOnMock invocation) throws Throwable {
 259                 return actual.abort();
 260             }
 261         }).when(cohort).abort();
 262
 263         doAnswer(new Answer<DataTreeCandidateTip>() {
 264             @Override
 265             public DataTreeCandidateTip answer(final InvocationOnMock invocation) {
 266                 return actual.getCandidate();
 267             }
 268         }).when(cohort).getCandidate();
 269
 270         return cohort;
 271     }
 272
 273     protected Object prepareReadyTransactionMessage(boolean remoteReadWriteTransaction, Shard shard, ShardDataTreeCohort cohort,
 274             TransactionIdentifier transactionID, MutableCompositeModification modification,
 275             boolean doCommitOnReady) {
 276         if(remoteReadWriteTransaction){
 277             return prepareForwardedReadyTransaction(cohort, transactionID, CURRENT_VERSION,
 278                     doCommitOnReady);
 279         } else {
 280             setupCohortDecorator(shard, cohort);
 281             return prepareBatchedModifications(transactionID, modification, doCommitOnReady);
 282         }
 283     }
 284
 285     protected ShardDataTreeCohort mockShardDataTreeCohort() {
 286         ShardDataTreeCohort cohort = mock(ShardDataTreeCohort.class);
 287         doReturn(Futures.immediateFuture(Boolean.TRUE)).when(cohort).canCommit();
 288         doReturn(Futures.immediateFuture(null)).when(cohort).preCommit();
 289         doReturn(Futures.immediateFuture(null)).when(cohort).commit();
 290         doReturn(mockCandidate("candidate")).when(cohort).getCandidate();
 291         return cohort;
 292     }
 293
 294     static ShardDataTreeTransactionParent newShardDataTreeTransactionParent(ShardDataTreeCohort cohort) {
 295         ShardDataTreeTransactionParent mockParent = mock(ShardDataTreeTransactionParent.class);
 296         doReturn(cohort).when(mockParent).finishTransaction(any(ReadWriteShardDataTreeTransaction.class));
 297         doNothing().when(mockParent).abortTransaction(any(AbstractShardDataTreeTransaction.class));
 298         return mockParent;
 299     }
 300
 301     protected ForwardedReadyTransaction prepareForwardedReadyTransaction(ShardDataTreeCohort cohort,
 302             TransactionIdentifier transactionID, short version, boolean doCommitOnReady) {
 303         return new ForwardedReadyTransaction(transactionID, version,
 304                 new ReadWriteShardDataTreeTransaction(newShardDataTreeTransactionParent(cohort), transactionID,
 305                         mock(DataTreeModification.class)), doCommitOnReady);
 306     }
 307
 308     protected Object prepareReadyTransactionMessage(boolean remoteReadWriteTransaction, Shard shard, ShardDataTreeCohort cohort,
 309             TransactionIdentifier transactionID, MutableCompositeModification modification) {
 310         return prepareReadyTransactionMessage(remoteReadWriteTransaction, shard, cohort, transactionID, modification, false);
 311     }
 312
 313     protected void setupCohortDecorator(Shard shard, final ShardDataTreeCohort cohort) {
 314         shard.getCommitCoordinator().setCohortDecorator(new ShardCommitCoordinator.CohortDecorator() {
 315             @Override
 316             public ShardDataTreeCohort decorate(Identifier transactionID, ShardDataTreeCohort actual) {
 317                 return cohort;
 318             }
 319         });
 320     }
 321
 322     protected BatchedModifications prepareBatchedModifications(TransactionIdentifier transactionID,
 323                                                                MutableCompositeModification modification) {
 324         return prepareBatchedModifications(transactionID, modification, false);
 325     }
 326
 327     private static BatchedModifications prepareBatchedModifications(TransactionIdentifier transactionID,
 328                                                              MutableCompositeModification modification,
 329                                                              boolean doCommitOnReady) {
 330         final BatchedModifications batchedModifications = new BatchedModifications(transactionID, CURRENT_VERSION);
 331         batchedModifications.addModification(modification);
 332         batchedModifications.setReady(true);
 333         batchedModifications.setDoCommitOnReady(doCommitOnReady);
 334         batchedModifications.setTotalMessagesSent(1);
 335         return batchedModifications;
 336     }
 337
 338
 339     public static NormalizedNode<?,?> readStore(final TestActorRef<? extends Shard> shard, final YangInstanceIdentifier id)
 340             throws ExecutionException, InterruptedException {
 341         return shard.underlyingActor().getDataStore().readNode(id).orNull();
 342     }
 343
 344     public static NormalizedNode<?,?> readStore(final DataTree store, final YangInstanceIdentifier id) {
 345         return store.takeSnapshot().readNode(id).orNull();
 346     }
 347
 348     public void writeToStore(final TestActorRef<Shard> shard, final YangInstanceIdentifier id,
 349             final NormalizedNode<?,?> node) throws InterruptedException, ExecutionException {
 350         Future<Object> future = Patterns.ask(shard, newBatchedModifications(nextTransactionId(), id, node, true, true, 1),
 351                 new Timeout(5, TimeUnit.SECONDS));
 352         try {
 353             Await.ready(future, Duration.create(5, TimeUnit.SECONDS));
 354         } catch(TimeoutException e) {
 355             throw new ExecutionException(e);
 356         }
 357     }
 358
 359     public static void writeToStore(final ShardDataTree store, final YangInstanceIdentifier id,
 360             final NormalizedNode<?,?> node) throws InterruptedException, ExecutionException {
 361         final ReadWriteShardDataTreeTransaction transaction = store.newReadWriteTransaction(nextTransactionId());
 362
 363         transaction.getSnapshot().write(id, node);
 364         final ShardDataTreeCohort cohort = transaction.ready();
 365         cohort.canCommit().get();
 366         cohort.preCommit().get();
 367         cohort.commit();
 368     }
 369
 370     public void mergeToStore(final ShardDataTree store, final YangInstanceIdentifier id,
 371             final NormalizedNode<?,?> node) throws InterruptedException, ExecutionException {
 372         final ReadWriteShardDataTreeTransaction transaction = store.newReadWriteTransaction(nextTransactionId());
 373
 374         transaction.getSnapshot().merge(id, node);
 375         final ShardDataTreeCohort cohort = transaction.ready();
 376         cohort.canCommit().get();
 377         cohort.preCommit().get();
 378         cohort.commit();
 379     }
 380
 381     public static void writeToStore(final DataTree store, final YangInstanceIdentifier id,
 382             final NormalizedNode<?,?> node) throws DataValidationFailedException {
 383         final DataTreeModification transaction = store.takeSnapshot().newModification();
 384
 385         transaction.write(id, node);
 386         transaction.ready();
 387         store.validate(transaction);
 388         final DataTreeCandidate candidate = store.prepare(transaction);
 389         store.commit(candidate);
 390     }
 391
 392     DataTree setupInMemorySnapshotStore() throws DataValidationFailedException {
 393         final DataTree testStore = InMemoryDataTreeFactory.getInstance().create(TreeType.OPERATIONAL);
 394         testStore.setSchemaContext(SCHEMA_CONTEXT);
 395
 396         writeToStore(testStore, TestModel.TEST_PATH, ImmutableNodes.containerNode(TestModel.TEST_QNAME));
 397
 398         final NormalizedNode<?, ?> root = readStore(testStore, YangInstanceIdentifier.EMPTY);
 399
 400         InMemorySnapshotStore.addSnapshot(shardID.toString(), Snapshot.create(
 401                 SerializationUtils.serializeNormalizedNode(root),
 402                 Collections.<ReplicatedLogEntry>emptyList(), 0, 1, -1, -1));
 403         return testStore;
 404     }
 405
 406     static DataTreeCandidatePayload payloadForModification(final DataTree source, final DataTreeModification mod) throws DataValidationFailedException {
 407         source.validate(mod);
 408         final DataTreeCandidate candidate = source.prepare(mod);
 409         source.commit(candidate);
 410         return DataTreeCandidatePayload.create(candidate);
 411     }
 412
 413     static BatchedModifications newBatchedModifications(final TransactionIdentifier transactionID,
 414             final YangInstanceIdentifier path, final NormalizedNode<?, ?> data, final boolean ready, final boolean doCommitOnReady,
 415             final int messagesSent) {
 416         final BatchedModifications batched = new BatchedModifications(transactionID, CURRENT_VERSION);
 417         batched.addModification(new WriteModification(path, data));
 418         batched.setReady(ready);
 419         batched.setDoCommitOnReady(doCommitOnReady);
 420         batched.setTotalMessagesSent(messagesSent);
 421         return batched;
 422     }
 423
 424     @SuppressWarnings("unchecked")
 425     static void verifyOuterListEntry(final TestActorRef<Shard> shard, final Object expIDValue) throws Exception {
 426         final NormalizedNode<?, ?> outerList = readStore(shard, TestModel.OUTER_LIST_PATH);
 427         assertNotNull(TestModel.OUTER_LIST_QNAME.getLocalName() + " not found", outerList);
 428         assertTrue(TestModel.OUTER_LIST_QNAME.getLocalName() + " value is not Iterable",
 429                 outerList.getValue() instanceof Iterable);
 430         final Object entry = ((Iterable<Object>)outerList.getValue()).iterator().next();
 431         assertTrue(TestModel.OUTER_LIST_QNAME.getLocalName() + " entry is not MapEntryNode",
 432                 entry instanceof MapEntryNode);
 433         final MapEntryNode mapEntry = (MapEntryNode)entry;
 434         final Optional<DataContainerChild<? extends PathArgument, ?>> idLeaf =
 435                 mapEntry.getChild(new YangInstanceIdentifier.NodeIdentifier(TestModel.ID_QNAME));
 436         assertTrue("Missing leaf " + TestModel.ID_QNAME.getLocalName(), idLeaf.isPresent());
 437         assertEquals(TestModel.ID_QNAME.getLocalName() + " value", expIDValue, idLeaf.get().getValue());
 438     }
 439
 440     public static DataTreeCandidateTip mockCandidate(final String name) {
 441         final DataTreeCandidateTip mockCandidate = mock(DataTreeCandidateTip.class, name);
 442         final DataTreeCandidateNode mockCandidateNode = mock(DataTreeCandidateNode.class, name + "-node");
 443         doReturn(ModificationType.WRITE).when(mockCandidateNode).getModificationType();
 444         doReturn(Optional.of(ImmutableNodes.containerNode(CarsModel.CARS_QNAME))).when(mockCandidateNode).getDataAfter();
 445         doReturn(CarsModel.BASE_PATH).when(mockCandidate).getRootPath();
 446         doReturn(mockCandidateNode).when(mockCandidate).getRootNode();
 447         return mockCandidate;
 448     }
 449
 450     static DataTreeCandidateTip mockUnmodifiedCandidate(final String name) {
 451         final DataTreeCandidateTip mockCandidate = mock(DataTreeCandidateTip.class, name);
 452         final DataTreeCandidateNode mockCandidateNode = mock(DataTreeCandidateNode.class, name + "-node");
 453         doReturn(ModificationType.UNMODIFIED).when(mockCandidateNode).getModificationType();
 454         doReturn(YangInstanceIdentifier.EMPTY).when(mockCandidate).getRootPath();
 455         doReturn(mockCandidateNode).when(mockCandidate).getRootNode();
 456         return mockCandidate;
 457     }
 458
 459     static void commitTransaction(final DataTree store, final DataTreeModification modification) throws DataValidationFailedException {
 460         modification.ready();
 461         store.validate(modification);
 462         store.commit(store.prepare(modification));
 463     }
 464
 465     @SuppressWarnings("serial")
 466     public static final class DelegatingShardCreator implements Creator<Shard> {
 467         private final Creator<Shard> delegate;
 468
 469         DelegatingShardCreator(final Creator<Shard> delegate) {
 470             this.delegate = delegate;
 471         }
 472
 473         @Override
 474         public Shard create() throws Exception {
 475             return delegate.create();
 476         }
 477     }
 478 }