Add further optimizations for Consensus Commit

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

@@ -144,7 +144,7 @@ public DistributedTransaction begin() {
 
   @Override
   public DistributedTransaction begin(String txId) {
-    return begin(txId, config.getIsolation(), false);
+    return begin(txId, config.getIsolation(), false, false);
   }
 
   @Override
@@ -155,7 +155,7 @@ public DistributedTransaction beginReadOnly() {
 
   @Override
   public DistributedTransaction beginReadOnly(String txId) {
-    return begin(txId, config.getIsolation(), true);
+    return begin(txId, config.getIsolation(), true, false);
   }
 
   /** @deprecated As of release 2.4.0. Will be removed in release 4.0.0. */
@@ -169,7 +169,7 @@ public DistributedTransaction start(com.scalar.db.api.Isolation isolation) {
   @Deprecated
   @Override
   public DistributedTransaction start(String txId, com.scalar.db.api.Isolation isolation) {
-    return begin(txId, Isolation.valueOf(isolation.name()), false);
+    return begin(txId, Isolation.valueOf(isolation.name()), false, false);
   }
 
   /** @deprecated As of release 2.4.0. Will be removed in release 4.0.0. */
@@ -192,7 +192,7 @@ public DistributedTransaction start(com.scalar.db.api.SerializableStrategy strat
   @Override
   public DistributedTransaction start(
       String txId, com.scalar.db.api.SerializableStrategy strategy) {
-    return begin(txId, Isolation.SERIALIZABLE, false);
+    return begin(txId, Isolation.SERIALIZABLE, false, false);
   }
 
   /** @deprecated As of release 2.4.0. Will be removed in release 4.0.0. */
@@ -202,23 +202,24 @@ public DistributedTransaction start(
       String txId,
       com.scalar.db.api.Isolation isolation,
       com.scalar.db.api.SerializableStrategy strategy) {
-    return begin(txId, Isolation.valueOf(isolation.name()), false);
+    return begin(txId, Isolation.valueOf(isolation.name()), false, false);
   }
 
   @VisibleForTesting
   DistributedTransaction begin(Isolation isolation) {
     String txId = UUID.randomUUID().toString();
-    return begin(txId, isolation, false);
+    return begin(txId, isolation, false, false);
   }
 
   @VisibleForTesting
   DistributedTransaction beginReadOnly(Isolation isolation) {
     String txId = UUID.randomUUID().toString();
-    return begin(txId, isolation, true);
+    return begin(txId, isolation, true, false);
   }
 
   @VisibleForTesting
-  DistributedTransaction begin(String txId, Isolation isolation, boolean readOnly) {
+  DistributedTransaction begin(
+      String txId, Isolation isolation, boolean readOnly, boolean oneOperation) {
     checkArgument(!Strings.isNullOrEmpty(txId));
     checkNotNull(isolation);
     if (isGroupCommitEnabled()) {
@@ -238,7 +239,8 @@ DistributedTransaction begin(String txId, Isolation isolation, boolean readOnly)
             tableMetadataManager,
             isIncludeMetadataEnabled,
             parallelExecutor,
-            readOnly);
+            readOnly,
+            oneOperation);
     DistributedTransaction transaction =
         new ConsensusCommit(crud, commit, recovery, mutationOperationChecker, groupCommitter);
     if (readOnly) {
@@ -249,6 +251,11 @@ DistributedTransaction begin(String txId, Isolation isolation, boolean readOnly)
     return transaction;
   }
 
+  private DistributedTransaction beginOneOperation(boolean readOnly) {
+    String txId = UUID.randomUUID().toString();
+    return begin(txId, config.getIsolation(), readOnly, true);
+  }
+
   @Override
   public Optional<Result> get(Get get) throws CrudException, UnknownTransactionStatusException {
     return executeTransaction(t -> t.get(copyAndSetTargetToIfNot(get)), true);
@@ -261,7 +268,7 @@ public List<Result> scan(Scan scan) throws CrudException, UnknownTransactionStat
 
   @Override
   public Scanner getScanner(Scan scan) throws CrudException {
-    DistributedTransaction transaction = beginReadOnly();
+    DistributedTransaction transaction = beginOneOperation(true);
 
     TransactionCrudOperable.Scanner scanner;
     try {
@@ -431,12 +438,7 @@ private <R> R executeTransaction(
       ThrowableFunction<DistributedTransaction, R, TransactionException> throwableFunction,
       boolean readOnly)
       throws CrudException, UnknownTransactionStatusException {
-    DistributedTransaction transaction;
-    if (readOnly) {
-      transaction = beginReadOnly();
-    } else {
-      transaction = begin();
-    }
+    DistributedTransaction transaction = beginOneOperation(readOnly);
 
     try {
       R result = throwableFunction.apply(transaction);

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

@@ -51,6 +51,11 @@ public class CrudHandler {
   // Whether the transaction is in read-only mode or not.
   private final boolean readOnly;
 
+  // Whether the transaction is in one-operation mode or not. One-operation mode refers to executing
+  // a CRUD operation directly through `DistributedTransactionManager` without explicitly beginning
+  // a transaction.
+  private final boolean oneOperation;
+
   private final List<ConsensusCommitScanner> scanners = new ArrayList<>();
 
   @SuppressFBWarnings("EI_EXPOSE_REP2")
@@ -60,14 +65,16 @@ public CrudHandler(
       TransactionTableMetadataManager tableMetadataManager,
       boolean isIncludeMetadataEnabled,
       ParallelExecutor parallelExecutor,
-      boolean readOnly) {
+      boolean readOnly,
+      boolean oneOperation) {
     this.storage = checkNotNull(storage);
     this.snapshot = checkNotNull(snapshot);
     this.tableMetadataManager = tableMetadataManager;
     this.isIncludeMetadataEnabled = isIncludeMetadataEnabled;
     this.mutationConditionsValidator = new MutationConditionsValidator(snapshot.getId());
     this.parallelExecutor = parallelExecutor;
     this.readOnly = readOnly;
+    this.oneOperation = oneOperation;
   }
 
   @VisibleForTesting
@@ -78,14 +85,16 @@ public CrudHandler(
       boolean isIncludeMetadataEnabled,
       MutationConditionsValidator mutationConditionsValidator,
       ParallelExecutor parallelExecutor,
-      boolean readOnly) {
+      boolean readOnly,
+      boolean oneOperation) {
     this.storage = checkNotNull(storage);
     this.snapshot = checkNotNull(snapshot);
     this.tableMetadataManager = tableMetadataManager;
     this.isIncludeMetadataEnabled = isIncludeMetadataEnabled;
     this.mutationConditionsValidator = mutationConditionsValidator;
     this.parallelExecutor = parallelExecutor;
     this.readOnly = readOnly;
+    this.oneOperation = oneOperation;
   }
 
   public Optional<Result> get(Get originalGet) throws CrudException {
@@ -102,11 +111,17 @@ public Optional<Result> get(Get originalGet) throws CrudException {
       key = new Snapshot.Key(get);
     }
 
-    readUnread(key, get);
-
-    return snapshot
-        .getResult(key, get)
-        .map(r -> new FilteredResult(r, originalProjections, metadata, isIncludeMetadataEnabled));
+    if (isSnapshotReadRequired()) {
+      readUnread(key, get);
+      return snapshot
+          .getResult(key, get)
+          .map(r -> new FilteredResult(r, originalProjections, metadata, isIncludeMetadataEnabled));
+    } else {
+      Optional<TransactionResult> result = read(key, get);
+      return snapshot
+          .mergeResult(key, result, get.getConjunctions())
+          .map(r -> new FilteredResult(r, originalProjections, metadata, isIncludeMetadataEnabled));
+    }
   }
 
   // Only for a Get with index, the argument `key` is null
@@ -120,7 +135,7 @@ void readUnread(@Nullable Snapshot.Key key, Get get) throws CrudException {
   // Although this class is not thread-safe, this method is actually thread-safe, so we call it
   // concurrently in the implicit pre-read
   @VisibleForTesting
-  void read(@Nullable Snapshot.Key key, Get get) throws CrudException {
+  Optional<TransactionResult> read(@Nullable Snapshot.Key key, Get get) throws CrudException {
     Optional<TransactionResult> result = getFromStorage(get);
     if (!result.isPresent() || result.get().isCommitted()) {
       if (result.isPresent() || get.getConjunctions().isEmpty()) {
@@ -142,8 +157,8 @@ void read(@Nullable Snapshot.Key key, Get get) throws CrudException {
           }
         }
       }
-      snapshot.putIntoGetSet(get, result);
-      return;
+      putIntoGetSetInSnapshot(get, result);
+      return result;
     }
     throw new UncommittedRecordException(
         get,
@@ -204,7 +219,7 @@ private LinkedHashMap<Snapshot.Key, TransactionResult> scanInternal(Scan scan)
       }
     }
 
-    snapshot.putIntoScanSet(scan, results);
+    putIntoScanSetInSnapshot(scan, results);
 
     return results;
   }
@@ -263,9 +278,43 @@ private void putIntoReadSetInSnapshot(Snapshot.Key key, Optional<TransactionResu
     }
   }
 
+  private boolean isSnapshotReadRequired() {
+    // In one-operation mode, we don't need snapshot read
+    return !oneOperation;
+  }
+
+  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
+    // the get set
+    if (isValidationOrSnapshotReadRequired()) {
+      snapshot.putIntoGetSet(get, 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
+    // the scan set
+    if (isValidationOrSnapshotReadRequired()) {
+      snapshot.putIntoScanSet(scan, results);
+    }
+  }
+
+  private void putIntoScannerSetInSnapshot(
+      Scan scan, LinkedHashMap<Snapshot.Key, TransactionResult> results) {
+    // if validation is not required, we don't need to put the results into the scanner set
+    if (snapshot.isValidationRequired()) {
+      snapshot.putIntoScannerSet(scan, results);
+    }
+  }
+
   private void verifyNoOverlap(Scan scan, Map<Snapshot.Key, TransactionResult> results) {
-    // In read-only mode, we don't need to verify the overlap
-    if (!readOnly) {
+    // In either read-only mode or one-operation mode, we don't need to verify the overlap
+    if (!readOnly && !oneOperation) {
       snapshot.verifyNoOverlap(scan, results);
     }
   }
@@ -432,7 +481,7 @@ private class ConsensusCommitStorageScanner extends AbstractTransactionCrudOpera
     private final List<String> originalProjections;
     private final Scanner scanner;
 
-    private final LinkedHashMap<Snapshot.Key, TransactionResult> results = new LinkedHashMap<>();
+    @Nullable private final LinkedHashMap<Snapshot.Key, TransactionResult> results;
     private final AtomicBoolean fullyScanned = new AtomicBoolean();
     private final AtomicBoolean closed = new AtomicBoolean();
 
@@ -441,6 +490,14 @@ public ConsensusCommitStorageScanner(Scan scan, List<String> originalProjections
       this.scan = scan;
       this.originalProjections = originalProjections;
       scanner = scanFromStorage(scan);
+
+      if (isValidationOrSnapshotReadRequired()) {
+        results = new LinkedHashMap<>();
+      } else {
+        // If neither validation nor snapshot read is required, we don't need to put the results
+        // into the scan set
+        results = null;
+      }
     }
 
     @Override
@@ -456,7 +513,10 @@ public Optional<Result> one() throws CrudException {
         Snapshot.Key key = new Snapshot.Key(scan, r.get());
         TransactionResult result = new TransactionResult(r.get());
         processScanResult(key, scan, result);
-        results.put(key, result);
+
+        if (results != null) {
+          results.put(key, result);
+        }
 
         TableMetadata metadata = getTableMetadata(scan);
         return Optional.of(
@@ -499,10 +559,10 @@ public void close() {
       if (fullyScanned.get()) {
         // If the scanner is fully scanned, we can treat it as a normal scan, and put the results
         // into the scan set
-        snapshot.putIntoScanSet(scan, results);
+        putIntoScanSetInSnapshot(scan, results);
       } else {
         // If the scanner is not fully scanned, put the results into the scanner set
-        snapshot.putIntoScannerSet(scan, results);
+        putIntoScannerSetInSnapshot(scan, results);
       }
 
       verifyNoOverlap(scan, results);

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

@@ -249,18 +249,22 @@ private Optional<TransactionResult> mergeResult(Key key, Optional<TransactionRes
     }
   }
 
-  private Optional<TransactionResult> mergeResult(
+  public Optional<TransactionResult> mergeResult(
       Key key, Optional<TransactionResult> result, Set<Conjunction> conjunctions)
       throws CrudException {
-    return mergeResult(key, result)
-        .filter(
-            r ->
-                // We need to apply conditions if it is a merged result because the transaction’s
-                // write makes the record no longer match the conditions. Of course, we can just
-                // return the result without checking the condition if there is no condition.
-                !r.isMergedResult()
-                    || conjunctions.isEmpty()
-                    || ScalarDbUtils.columnsMatchAnyOfConjunctions(r.getColumns(), conjunctions));
+    Optional<TransactionResult> ret = mergeResult(key, result);
+
+    if (conjunctions.isEmpty()) {
+      // We can just return the result without checking the condition if there is no condition.
+      return ret;
+    }
+
+    return ret.filter(
+        r ->
+            // We need to apply conditions if it is a merged result because the transaction’s write
+            // makes the record no longer match the conditions.
+            !r.isMergedResult()
+                || ScalarDbUtils.columnsMatchAnyOfConjunctions(r.getColumns(), conjunctions));
   }
 
   private TableMetadata getTableMetadata(Key key) throws CrudException {