Add READ_COMMITTED isolation

core/src/main/java/com/scalar/db/transaction/consensuscommit/ConsensusCommit.java

@@ -198,6 +198,8 @@ public void commit() throws CommitException, UnknownTransactionStatusException {
 
     try {
       crud.waitForRecoveryCompletionIfNecessary();
+    } catch (CrudConflictException e) {
+      throw new CommitConflictException(e.getMessage(), e, getId());
     } catch (CrudException e) {
       throw new CommitException(e.getMessage(), e, getId());
     }

core/src/main/java/com/scalar/db/transaction/consensuscommit/ConsensusCommitManager.java

@@ -48,12 +48,12 @@ public class ConsensusCommitManager extends AbstractDistributedTransactionManage
   private static final Logger logger = LoggerFactory.getLogger(ConsensusCommitManager.class);
   private final DistributedStorage storage;
   private final DistributedStorageAdmin admin;
-  private final ConsensusCommitConfig config;
   private final TransactionTableMetadataManager tableMetadataManager;
   private final Coordinator coordinator;
   private final ParallelExecutor parallelExecutor;
   private final RecoveryExecutor recoveryExecutor;
   protected final CommitHandler commit;
+  private final Isolation isolation;
   private final boolean isIncludeMetadataEnabled;
   private final ConsensusCommitMutationOperationChecker mutationOperationChecker;
   @Nullable private final CoordinatorGroupCommitter groupCommitter;
@@ -65,7 +65,7 @@ public ConsensusCommitManager(
     super(databaseConfig);
     this.storage = storage;
     this.admin = admin;
-    config = new ConsensusCommitConfig(databaseConfig);
+    ConsensusCommitConfig config = new ConsensusCommitConfig(databaseConfig);
     coordinator = new Coordinator(storage, config);
     parallelExecutor = new ParallelExecutor(config);
     tableMetadataManager =
@@ -74,7 +74,8 @@ public ConsensusCommitManager(
     RecoveryHandler recovery = new RecoveryHandler(storage, coordinator, tableMetadataManager);
     recoveryExecutor = new RecoveryExecutor(coordinator, recovery, tableMetadataManager);
     groupCommitter = CoordinatorGroupCommitter.from(config).orElse(null);
-    commit = createCommitHandler();
+    commit = createCommitHandler(config);
+    isolation = config.getIsolation();
     isIncludeMetadataEnabled = config.isIncludeMetadataEnabled();
     mutationOperationChecker = new ConsensusCommitMutationOperationChecker(tableMetadataManager);
   }
@@ -85,7 +86,7 @@ protected ConsensusCommitManager(DatabaseConfig databaseConfig) {
     storage = storageFactory.getStorage();
     admin = storageFactory.getStorageAdmin();
 
-    config = new ConsensusCommitConfig(databaseConfig);
+    ConsensusCommitConfig config = new ConsensusCommitConfig(databaseConfig);
     coordinator = new Coordinator(storage, config);
     parallelExecutor = new ParallelExecutor(config);
     tableMetadataManager =
@@ -94,7 +95,8 @@ protected ConsensusCommitManager(DatabaseConfig databaseConfig) {
     RecoveryHandler recovery = new RecoveryHandler(storage, coordinator, tableMetadataManager);
     recoveryExecutor = new RecoveryExecutor(coordinator, recovery, tableMetadataManager);
     groupCommitter = CoordinatorGroupCommitter.from(config).orElse(null);
-    commit = createCommitHandler();
+    commit = createCommitHandler(config);
+    isolation = config.getIsolation();
     isIncludeMetadataEnabled = config.isIncludeMetadataEnabled();
     mutationOperationChecker = new ConsensusCommitMutationOperationChecker(tableMetadataManager);
   }
@@ -104,17 +106,17 @@ protected ConsensusCommitManager(DatabaseConfig databaseConfig) {
   ConsensusCommitManager(
       DistributedStorage storage,
       DistributedStorageAdmin admin,
-      ConsensusCommitConfig config,
       DatabaseConfig databaseConfig,
       Coordinator coordinator,
       ParallelExecutor parallelExecutor,
       RecoveryExecutor recoveryExecutor,
       CommitHandler commit,
+      Isolation isolation,
+      boolean isIncludeMetadataEnabled,
       @Nullable CoordinatorGroupCommitter groupCommitter) {
     super(databaseConfig);
     this.storage = storage;
     this.admin = admin;
-    this.config = config;
     tableMetadataManager =
         new TransactionTableMetadataManager(
             admin, databaseConfig.getMetadataCacheExpirationTimeSecs());
@@ -123,13 +125,14 @@ protected ConsensusCommitManager(DatabaseConfig databaseConfig) {
     this.recoveryExecutor = recoveryExecutor;
     this.commit = commit;
     this.groupCommitter = groupCommitter;
-    this.isIncludeMetadataEnabled = config.isIncludeMetadataEnabled();
+    this.isolation = isolation;
+    this.isIncludeMetadataEnabled = isIncludeMetadataEnabled;
     this.mutationOperationChecker =
         new ConsensusCommitMutationOperationChecker(tableMetadataManager);
   }
 
   // `groupCommitter` must be set before calling this method.
-  private CommitHandler createCommitHandler() {
+  private CommitHandler createCommitHandler(ConsensusCommitConfig config) {
     if (isGroupCommitEnabled()) {
       return new CommitHandlerWithGroupCommit(
           storage,
@@ -156,7 +159,7 @@ public DistributedTransaction begin() {
 
   @Override
   public DistributedTransaction begin(String txId) {
-    return begin(txId, config.getIsolation(), false, false);
+    return begin(txId, isolation, false, false);
   }
 
   @Override
@@ -167,14 +170,15 @@ public DistributedTransaction beginReadOnly() {
 
   @Override
   public DistributedTransaction beginReadOnly(String txId) {
-    return begin(txId, config.getIsolation(), true, false);
+    return begin(txId, isolation, true, false);
   }
 
   /** @deprecated As of release 2.4.0. Will be removed in release 4.0.0. */
   @Deprecated
   @Override
   public DistributedTransaction start(com.scalar.db.api.Isolation isolation) {
-    return begin(Isolation.valueOf(isolation.name()));
+    String txId = UUID.randomUUID().toString();
+    return begin(txId, Isolation.valueOf(isolation.name()), false, false);
   }
 
   /** @deprecated As of release 2.4.0. Will be removed in release 4.0.0. */
@@ -189,14 +193,16 @@ public DistributedTransaction start(String txId, com.scalar.db.api.Isolation iso
   @Override
   public DistributedTransaction start(
       com.scalar.db.api.Isolation isolation, com.scalar.db.api.SerializableStrategy strategy) {
-    return begin(Isolation.valueOf(isolation.name()));
+    String txId = UUID.randomUUID().toString();
+    return begin(txId, Isolation.valueOf(isolation.name()), false, false);
   }
 
   /** @deprecated As of release 2.4.0. Will be removed in release 4.0.0. */
   @Deprecated
   @Override
   public DistributedTransaction start(com.scalar.db.api.SerializableStrategy strategy) {
-    return begin(Isolation.SERIALIZABLE);
+    String txId = UUID.randomUUID().toString();
+    return begin(txId, Isolation.SERIALIZABLE, false, false);
   }
 
   /** @deprecated As of release 2.4.0. Will be removed in release 4.0.0. */
@@ -217,18 +223,6 @@ public DistributedTransaction start(
     return begin(txId, Isolation.valueOf(isolation.name()), false, false);
   }
 
-  @VisibleForTesting
-  DistributedTransaction begin(Isolation isolation) {
-    String txId = UUID.randomUUID().toString();
-    return begin(txId, isolation, false, false);
-  }
-
-  @VisibleForTesting
-  DistributedTransaction beginReadOnly(Isolation isolation) {
-    String txId = UUID.randomUUID().toString();
-    return begin(txId, isolation, true, false);
-  }
-
   @VisibleForTesting
   DistributedTransaction begin(
       String txId, Isolation isolation, boolean readOnly, boolean oneOperation) {
@@ -238,7 +232,7 @@ DistributedTransaction begin(
       assert groupCommitter != null;
       txId = groupCommitter.reserve(txId);
     }
-    if (!config.getIsolation().equals(isolation)) {
+    if (!this.isolation.equals(isolation)) {
       logger.warn(
           "Setting different isolation level from the one in DatabaseConfig might cause unexpected "
               + "anomalies");
@@ -266,7 +260,7 @@ DistributedTransaction begin(
 
   private DistributedTransaction beginOneOperation(boolean readOnly) {
     String txId = UUID.randomUUID().toString();
-    return begin(txId, config.getIsolation(), readOnly, true);
+    return begin(txId, isolation, readOnly, true);
   }
 
   @Override

core/src/main/java/com/scalar/db/transaction/consensuscommit/CrudHandler.java

@@ -25,6 +25,7 @@
 import com.scalar.db.common.AbstractTransactionCrudOperableScanner;
 import com.scalar.db.common.error.CoreError;
 import com.scalar.db.exception.storage.ExecutionException;
+import com.scalar.db.exception.transaction.CrudConflictException;
 import com.scalar.db.exception.transaction.CrudException;
 import com.scalar.db.util.ScalarDbUtils;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
@@ -196,8 +197,26 @@ Optional<TransactionResult> read(@Nullable Snapshot.Key key, Get get) throws Cru
 
   private Optional<TransactionResult> executeRecovery(
       Snapshot.Key key, Selection selection, TransactionResult result) throws CrudException {
+    RecoveryExecutor.RecoveryType recoveryType;
+    if (snapshot.getIsolation() == Isolation.READ_COMMITTED) {
+      // In READ_COMMITTED isolation
+
+      if (readOnly) {
+        // In read-only mode, we don't recover the record, but return the committed result
+        recoveryType = RecoveryExecutor.RecoveryType.RETURN_COMMITTED_RESULT_AND_NOT_RECOVER;
+      } else {
+        // In read-write mode, we recover the record and return the committed result
+        recoveryType = RecoveryExecutor.RecoveryType.RETURN_COMMITTED_RESULT_AND_RECOVER;
+      }
+    } else {
+      // In SNAPSHOT or SERIALIZABLE isolation, we always recover the record and return the latest
+      // result
+      recoveryType = RecoveryExecutor.RecoveryType.RETURN_LATEST_RESULT_AND_RECOVER;
+    }
+
     RecoveryExecutor.Result recoveryResult =
-        recoveryExecutor.execute(key, selection, result, snapshot.getId());
+        recoveryExecutor.execute(key, selection, result, snapshot.getId(), recoveryType);
+
     recoveryResults.add(recoveryResult);
     return recoveryResult.recoveredResult;
   }
@@ -337,16 +356,16 @@ private void putIntoReadSetInSnapshot(Snapshot.Key key, Optional<TransactionResu
   }
 
   private boolean isSnapshotReadRequired() {
-    // In one-operation mode, we don't need snapshot read
-    return !oneOperation;
+    // In one-operation mode, we don't need snapshot reads
+    return !oneOperation && snapshot.isSnapshotReadRequired();
   }
 
   private boolean isValidationOrSnapshotReadRequired() {
     return snapshot.isValidationRequired() || isSnapshotReadRequired();
   }
 
   private void putIntoGetSetInSnapshot(Get get, Optional<TransactionResult> result) {
-    // If neither validation nor snapshot read is required, we don't need to put the result into
+    // If neither validation nor snapshot reads are required, we don't need to put the result into
     // the get set
     if (isValidationOrSnapshotReadRequired()) {
       snapshot.putIntoGetSet(get, result);
@@ -355,7 +374,7 @@ private void putIntoGetSetInSnapshot(Get get, Optional<TransactionResult> result
 
   private void putIntoScanSetInSnapshot(
       Scan scan, LinkedHashMap<Snapshot.Key, TransactionResult> results) {
-    // If neither validation nor snapshot read is required, we don't need to put the results into
+    // If neither validation nor snapshot reads are required, we don't need to put the results into
     // the scan set
     if (isValidationOrSnapshotReadRequired()) {
       snapshot.putIntoScanSet(scan, results);
@@ -371,12 +390,16 @@ private void putIntoScannerSetInSnapshot(
   }
 
   private void verifyNoOverlap(Scan scan, Map<Snapshot.Key, TransactionResult> results) {
-    // In either read-only mode or one-operation mode, we don't need to verify the overlap
-    if (!readOnly && !oneOperation) {
+    if (isOverlapVerificationRequired()) {
       snapshot.verifyNoOverlap(scan, results);
     }
   }
 
+  private boolean isOverlapVerificationRequired() {
+    // In either read-only mode or one-operation mode, we don't need to verify overlap
+    return !readOnly && !oneOperation;
+  }
+
   public void put(Put put) throws CrudException {
     Snapshot.Key key = new Snapshot.Key(put);
 
@@ -476,6 +499,7 @@ private Get createGet(Snapshot.Key key) {
    *       complete, the validation could fail due to records with PREPARED or DELETED status.
    * </ul>
    *
+   * @throws CrudConflictException if any recovery task fails due to a conflict
    * @throws CrudException if any recovery task fails
    */
   public void waitForRecoveryCompletionIfNecessary() throws CrudException {
@@ -487,6 +511,11 @@ public void waitForRecoveryCompletionIfNecessary() throws CrudException {
           recoveryResult.recoveryFuture.get();
         }
       } catch (java.util.concurrent.ExecutionException e) {
+        if (e.getCause() instanceof CrudConflictException) {
+          throw new CrudConflictException(
+              e.getCause().getMessage(), e.getCause(), snapshot.getId());
+        }
+
         throw new CrudException(
             CoreError.CONSENSUS_COMMIT_RECOVERING_RECORDS_FAILED.buildMessage(
                 e.getCause().getMessage()),
@@ -507,6 +536,11 @@ void waitForRecoveryCompletion() throws CrudException {
       try {
         recoveryResult.recoveryFuture.get();
       } catch (java.util.concurrent.ExecutionException e) {
+        if (e.getCause() instanceof CrudConflictException) {
+          throw new CrudConflictException(
+              e.getCause().getMessage(), e.getCause(), snapshot.getId());
+        }
+
         throw new CrudException(
             CoreError.CONSENSUS_COMMIT_RECOVERING_RECORDS_FAILED.buildMessage(
                 e.getCause().getMessage()),
@@ -737,10 +771,10 @@ public ConsensusCommitStorageScanner(Scan scan, List<String> originalProjections
         scanner = scanFromStorage(scan);
       }
 
-      if (isValidationOrSnapshotReadRequired()) {
+      if (isValidationOrSnapshotReadRequired() || isOverlapVerificationRequired()) {
         results = new LinkedHashMap<>();
       } else {
-        // If neither validation nor snapshot read is required, we don't need to put the results
+        // If neither validation nor snapshot reads are required, we don't need to put the results
         // into the scan set
         results = null;
       }

core/src/main/java/com/scalar/db/transaction/consensuscommit/Isolation.java

@@ -1,6 +1,7 @@
 package com.scalar.db.transaction.consensuscommit;
 
 public enum Isolation {
+  READ_COMMITTED,
   SNAPSHOT,
   SERIALIZABLE,
 }