Read-Only TxnContext Interface; Read-Only (single-statement select, txn) optimizations

src/concurrency/timestamp_ordering_transaction_manager.cpp

@@ -590,6 +590,12 @@ ResultType TimestampOrderingTransactionManager::CommitTransaction(
   //// handle other isolation levels
   //////////////////////////////////////////////////////////
 
+  if (!current_txn->IsWritten()) {
+    LOG_TRACE("Transaction not yet written, ending transaction.");
+    EndTransaction(current_txn);
+    return ResultType::SUCCESS;
+  }
+
   auto storage_manager = storage::StorageManager::GetInstance();
   auto &log_manager = logging::LogManager::GetInstance();
 

src/concurrency/transaction_context.cpp

@@ -48,22 +48,24 @@ namespace concurrency {
  *    i : insert
  */
 
-TransactionContext::TransactionContext(const size_t thread_id,
+TransactionContext::TransactionContext(bool read_only, const size_t thread_id,
                                        const IsolationLevelType isolation,
                                        const cid_t &read_id) {
-  Init(thread_id, isolation, read_id);
+  Init(read_only, thread_id, isolation, read_id);
 }
 
-TransactionContext::TransactionContext(const size_t thread_id,
+TransactionContext::TransactionContext(bool read_only, const size_t thread_id,
                                        const IsolationLevelType isolation,
                                        const cid_t &read_id,
                                        const cid_t &commit_id) {
-  Init(thread_id, isolation, read_id, commit_id);
+  Init(read_only, thread_id, isolation, read_id, commit_id);
 }
 
-void TransactionContext::Init(const size_t thread_id,
+void TransactionContext::Init(bool read_only, const size_t thread_id,
                               const IsolationLevelType isolation,
                               const cid_t &read_id, const cid_t &commit_id) {
+  read_only_ = read_only;
+
   read_id_ = read_id;
 
   // commit id can be set at a transaction's commit phase.

src/concurrency/transaction_manager.cpp

@@ -32,7 +32,7 @@ ConflictAvoidanceType TransactionManager::conflict_avoidance_ =
     ConflictAvoidanceType::ABORT;
 
 TransactionContext *TransactionManager::BeginTransaction(
-    const size_t thread_id, const IsolationLevelType type, bool read_only) {
+    bool read_only, const size_t thread_id, const IsolationLevelType type) {
   TransactionContext *txn = nullptr;
 
   if (type == IsolationLevelType::SNAPSHOT) {
@@ -45,9 +45,10 @@ TransactionContext *TransactionManager::BeginTransaction(
       cid_t commit_id = EpochManagerFactory::GetInstance().EnterEpoch(
           thread_id, TimestampType::COMMIT);
 
-      txn = new TransactionContext(thread_id, type, read_id, commit_id);
+      txn = new TransactionContext(read_only, thread_id, type, read_id,
+                                   commit_id);
     } else {
-      txn = new TransactionContext(thread_id, type, read_id);
+      txn = new TransactionContext(read_only, thread_id, type, read_id);
     }
 
   } else {
@@ -58,11 +59,7 @@ TransactionContext *TransactionManager::BeginTransaction(
     // transaction processing with decentralized epoch manager
     cid_t read_id = EpochManagerFactory::GetInstance().EnterEpoch(
         thread_id, TimestampType::READ);
-    txn = new TransactionContext(thread_id, type, read_id);
-  }
-
-  if (read_only) {
-    txn->SetReadOnly();
+    txn = new TransactionContext(read_only, thread_id, type, read_id);
   }
 
   txn->SetTimestamp(function::DateFunctions::Now());

src/include/concurrency/transaction_context.h

@@ -44,25 +44,27 @@ class TransactionContext : public Printable {
   TransactionContext(TransactionContext const &) = delete;
 
  public:
-  TransactionContext(const size_t thread_id, const IsolationLevelType isolation,
-              const cid_t &read_id);
+  TransactionContext(bool read_only, const size_t thread_id,
+                     const IsolationLevelType isolation, const cid_t &read_id);
 
-  TransactionContext(const size_t thread_id, const IsolationLevelType isolation,
-              const cid_t &read_id, const cid_t &commit_id);
+  TransactionContext(bool read_only, const size_t thread_id,
+                     const IsolationLevelType isolation, const cid_t &read_id,
+                     const cid_t &commit_id);
 
   /**
    * @brief      Destroys the object.
    */
   ~TransactionContext() = default;
 
  private:
-  void Init(const size_t thread_id, const IsolationLevelType isolation,
-            const cid_t &read_id) {
-    Init(thread_id, isolation, read_id, read_id);
+  void Init(bool read_only, const size_t thread_id,
+            const IsolationLevelType isolation, const cid_t &read_id) {
+    Init(read_only, thread_id, isolation, read_id, read_id);
   }
 
-  void Init(const size_t thread_id, const IsolationLevelType isolation,
-            const cid_t &read_id, const cid_t &commit_id);
+  void Init(bool read_only, const size_t thread_id,
+            const IsolationLevelType isolation, const cid_t &read_id,
+            const cid_t &commit_id);
 
  public:
   //===--------------------------------------------------------------------===//
@@ -264,12 +266,11 @@ class TransactionContext : public Printable {
   }
 
   /**
-   * @brief      mark this context as read only
+   * @brief      Determines if already written.
    *
+   * @return     True if already written, False otherwise.
    */
-  void SetReadOnly() {
-    read_only_ = true;
-  }
+  bool IsWritten() const { return is_written_; }
 
   /**
    * @brief      Gets the isolation level.

src/include/concurrency/transaction_manager.h

@@ -219,13 +219,19 @@ class TransactionManager {
     current_txn->SetResult(result);
   }
 
+  TransactionContext *BeginTransaction() { return BeginTransaction(false); }
+
+  TransactionContext *BeginTransaction(const size_t thread_id) {
+    return BeginTransaction(false, thread_id, isolation_level_);
+  }
+
   TransactionContext *BeginTransaction(const IsolationLevelType type) {
-    return BeginTransaction(0, type, false);
+    return BeginTransaction(false, 0, type);
   }
 
-  TransactionContext *BeginTransaction(const size_t thread_id = 0,
-                                const IsolationLevelType type = isolation_level_,
-                                bool read_only = false);
+  TransactionContext *BeginTransaction(
+      bool read_only, const size_t thread_id = 0,
+      const IsolationLevelType type = isolation_level_);
 
   /**
    * @brief      Ends a transaction.

src/traffic_cop/traffic_cop.cpp

@@ -164,7 +164,9 @@ executor::ExecutionResult TrafficCop::ExecuteHelper(
     // new txn, reset result status
     curr_state.second = ResultType::SUCCESS;
     single_statement_txn_ = true;
-    txn = txn_manager.BeginTransaction(thread_id);
+    // txn is read-only for single-statement select
+    bool read_only = statement_->GetQueryType() == QueryType::QUERY_SELECT;
+    txn = txn_manager.BeginTransaction(read_only, thread_id);
     tcop_txn_state_.emplace(txn, ResultType::SUCCESS);
   }
 

test/executor/copy_test.cpp

@@ -93,6 +93,7 @@ TEST_F(CopyTests, Copying) {
     std::vector<ResultValue> result;
 
     TestingSQLUtil::counter_.store(1);
+    traffic_cop.SetStatement(statement);
     executor::ExecutionResult status = traffic_cop.ExecuteHelper(
         statement->GetPlanTree(), params, result, result_format);
 

test/include/concurrency/testing_transaction_util.h

@@ -242,7 +242,8 @@ class TransactionThread {
     if (cur_seq == 0) {
       if (schedule->declared_ro == true) {
         /** starts a read only transaction*/
-        txn = txn_manager->BeginTransaction(0, IsolationLevelType::SNAPSHOT, true);
+        txn = txn_manager->BeginTransaction(true, 0,
+                                            IsolationLevelType::SNAPSHOT);
       } else {
         txn = txn_manager->BeginTransaction();
       }