Skip commit-state for read-only transactions

Author: brfrn169

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

@@ -106,42 +106,52 @@ private void waitBeforePreparationSnapshotHookFuture(
     }
   }
 
-  public void commit(Snapshot snapshot) throws CommitException, UnknownTransactionStatusException {
+  public void commit(Snapshot snapshot, boolean readOnly)
+      throws CommitException, UnknownTransactionStatusException {
+    boolean hasNoWritesAndDeletesInSnapshot = readOnly || snapshot.hasNoWritesAndDeletes();
+
     Optional<Future<Void>> snapshotHookFuture = invokeBeforePreparationSnapshotHook(snapshot);
-    try {
-      prepare(snapshot);
-    } catch (PreparationException e) {
-      safelyCallOnFailureBeforeCommit(snapshot);
-      abortState(snapshot.getId());
-      rollbackRecords(snapshot);
-      if (e instanceof PreparationConflictException) {
-        throw new CommitConflictException(e.getMessage(), e, e.getTransactionId().orElse(null));
+
+    if (!hasNoWritesAndDeletesInSnapshot) {
+      try {
+        prepare(snapshot);
+      } catch (PreparationException e) {
+        safelyCallOnFailureBeforeCommit(snapshot);
+        abortState(snapshot.getId());
+        rollbackRecords(snapshot);
+        if (e instanceof PreparationConflictException) {
+          throw new CommitConflictException(e.getMessage(), e, e.getTransactionId().orElse(null));
+        }
+        throw new CommitException(e.getMessage(), e, e.getTransactionId().orElse(null));
+      } catch (Exception e) {
+        safelyCallOnFailureBeforeCommit(snapshot);
+        throw e;
       }
-      throw new CommitException(e.getMessage(), e, e.getTransactionId().orElse(null));
-    } catch (Exception e) {
-      safelyCallOnFailureBeforeCommit(snapshot);
-      throw e;
     }
 
-    try {
-      validate(snapshot);
-    } catch (ValidationException e) {
-      safelyCallOnFailureBeforeCommit(snapshot);
-      abortState(snapshot.getId());
-      rollbackRecords(snapshot);
-      if (e instanceof ValidationConflictException) {
-        throw new CommitConflictException(e.getMessage(), e, e.getTransactionId().orElse(null));
+    if (!snapshot.hasNoReads()) {
+      try {
+        validate(snapshot);
+      } catch (ValidationException e) {
+        safelyCallOnFailureBeforeCommit(snapshot);
+        abortState(snapshot.getId());
+        rollbackRecords(snapshot);
+        if (e instanceof ValidationConflictException) {
+          throw new CommitConflictException(e.getMessage(), e, e.getTransactionId().orElse(null));
+        }
+        throw new CommitException(e.getMessage(), e, e.getTransactionId().orElse(null));
+      } catch (Exception e) {
+        safelyCallOnFailureBeforeCommit(snapshot);
+        throw e;
       }
-      throw new CommitException(e.getMessage(), e, e.getTransactionId().orElse(null));
-    } catch (Exception e) {
-      safelyCallOnFailureBeforeCommit(snapshot);
-      throw e;
     }
 
     waitBeforePreparationSnapshotHookFuture(snapshot, snapshotHookFuture.orElse(null));
 
-    commitState(snapshot);
-    commitRecords(snapshot);
+    if (!hasNoWritesAndDeletesInSnapshot) {
+      commitState(snapshot);
+      commitRecords(snapshot);
+    }
   }
 
   protected void handleCommitConflict(Snapshot snapshot, Exception cause)

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

@@ -5,6 +5,7 @@
 import com.scalar.db.api.DistributedStorage;
 import com.scalar.db.api.TransactionState;
 import com.scalar.db.exception.transaction.CommitConflictException;
+import com.scalar.db.exception.transaction.CommitException;
 import com.scalar.db.exception.transaction.UnknownTransactionStatusException;
 import com.scalar.db.transaction.consensuscommit.Coordinator.State;
 import com.scalar.db.util.groupcommit.Emittable;
@@ -37,6 +38,16 @@ public CommitHandlerWithGroupCommit(
     this.groupCommitter = groupCommitter;
   }
 
+  @Override
+  public void commit(Snapshot snapshot, boolean readOnly)
+      throws CommitException, UnknownTransactionStatusException {
+    if (!readOnly && snapshot.hasNoWritesAndDeletes()) {
+      cancelGroupCommitIfNeeded(snapshot.getId());
+    }
+
+    super.commit(snapshot, readOnly);
+  }
+
   @Override
   protected void onFailureBeforeCommit(Snapshot snapshot) {
     cancelGroupCommitIfNeeded(snapshot.getId());

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

@@ -269,7 +269,7 @@ public void commit() throws CommitException, UnknownTransactionStatusException {
           CoreError.CONSENSUS_COMMIT_EXECUTING_IMPLICIT_PRE_READ_FAILED.buildMessage(), e, getId());
     }
 
-    commit.commit(crud.getSnapshot());
+    commit.commit(crud.getSnapshot(), crud.isReadOnly());
   }
 
   @Override
@@ -280,7 +280,7 @@ public void rollback() {
       logger.warn("Failed to close the scanner", e);
     }
 
-    if (groupCommitter != null) {
+    if (groupCommitter != null && !crud.isReadOnly()) {
       groupCommitter.remove(crud.getSnapshot().getId());
     }
   }

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

@@ -221,7 +221,7 @@ DistributedTransaction beginReadOnly(Isolation isolation) {
   DistributedTransaction begin(String txId, Isolation isolation, boolean readOnly) {
     checkArgument(!Strings.isNullOrEmpty(txId));
     checkNotNull(isolation);
-    if (isGroupCommitEnabled()) {
+    if (!readOnly && isGroupCommitEnabled()) {
       assert groupCommitter != null;
       txId = groupCommitter.reserve(txId);
     }

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

@@ -420,6 +420,10 @@ public Snapshot getSnapshot() {
     return snapshot;
   }
 
+  public boolean isReadOnly() {
+    return readOnly;
+  }
+
   private interface ConsensusCommitScanner extends TransactionCrudOperable.Scanner {
     boolean isClosed();
   }

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

@@ -217,6 +217,14 @@ public boolean containsKeyInGetSet(Get get) {
     return getSet.containsKey(get);
   }
 
+  public boolean hasNoWritesAndDeletes() {
+    return writeSet.isEmpty() && deleteSet.isEmpty();
+  }
+
+  public boolean hasNoReads() {
+    return getSet.isEmpty() && scanSet.isEmpty() && scannerSet.isEmpty();
+  }
+
   public Optional<TransactionResult> getResult(Key key) throws CrudException {
     Optional<TransactionResult> result = readSet.getOrDefault(key, Optional.empty());
     return mergeResult(key, result);