Implement GraphDbAccessor creation for running transaction

Reviewers: dgleich

Reviewed By: dgleich

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1119

src/database/graph_db_accessor.cpp

@@ -14,6 +14,9 @@ namespace database {
 GraphDbAccessor::GraphDbAccessor(GraphDb &db)
     : db_(db), transaction_(*SingleNodeEngine().Begin()) {}
 
+GraphDbAccessor::GraphDbAccessor(GraphDb &db, tx::transaction_id_t tx_id)
+    : db_(db), transaction_(*db.tx_engine().RunningTransaction(tx_id)) {}
+
 GraphDbAccessor::~GraphDbAccessor() {
   if (!commited_ && !aborted_) {
     this->Abort();

src/database/graph_db_accessor.hpp

@@ -13,6 +13,7 @@
 #include "storage/vertex_accessor.hpp"
 #include "transactions/engine_single_node.hpp"
 #include "transactions/transaction.hpp"
+#include "transactions/type.hpp"
 #include "utils/bound.hpp"
 
 namespace database {
@@ -92,7 +93,13 @@ class GraphDbAccessor {
   };
 
  public:
+  /** Creates a new accessor by starting a new transaction. Only applicable to
+   * the single-node or distributed master. */
   explicit GraphDbAccessor(GraphDb &db);
+
+  /** Creates an accessor for a running transaction. Applicable to all types of
+   * memgraph. */
+  GraphDbAccessor(GraphDb &db, tx::transaction_id_t tx_id);
   ~GraphDbAccessor();
 
   GraphDbAccessor(const GraphDbAccessor &other) = delete;

src/transactions/engine.hpp

@@ -56,6 +56,9 @@ class Engine {
   virtual void LocalForEachActiveTransaction(
       std::function<void(Transaction &)> f) = 0;
 
+  /** Gets a transaction object for a running transaction. */
+  virtual tx::Transaction *RunningTransaction(tx::transaction_id_t tx_id) = 0;
+
   auto &local_lock_graph() { return local_lock_graph_; }
   const auto &local_lock_graph() const { return local_lock_graph_; }
 

src/transactions/engine_master.cpp

@@ -15,7 +15,8 @@ MasterEngine::MasterEngine(communication::messaging::System &system,
   rpc_server_.Register<SnapshotRpc>([this](const SnapshotReq &req) {
     // It is guaranteed that the Worker will not be requesting this for a
     // transaction that's done, and that there are no race conditions here.
-    return std::make_unique<SnapshotRes>(GetSnapshot(req.member));
+    return std::make_unique<SnapshotRes>(
+        RunningTransaction(req.member)->snapshot());
   });
 
   rpc_server_.Register<GcSnapshotRpc>(

src/transactions/engine_single_node.cpp

@@ -103,11 +103,12 @@ void SingleNodeEngine::LocalForEachActiveTransaction(
   }
 }
 
-Snapshot SingleNodeEngine::GetSnapshot(tx::transaction_id_t tx_id) {
+tx::Transaction *SingleNodeEngine::RunningTransaction(
+    tx::transaction_id_t tx_id) {
   std::lock_guard<SpinLock> guard(lock_);
   auto found = store_.find(tx_id);
-  DCHECK(found != store_.end())
+  CHECK(found != store_.end())
       << "Can't return snapshot for an inactive transaction";
-  return found->second->snapshot();
+  return found->second.get();
 }
 }  // namespace tx

src/transactions/engine_single_node.hpp

@@ -65,10 +65,7 @@ class SingleNodeEngine : public Engine {
   tx::transaction_id_t LocalLast() const override;
   void LocalForEachActiveTransaction(
       std::function<void(Transaction &)> f) override;
-
- protected:
-  // Exposed for MasterEngine. Transaction for tx_id must be alive.
-  Snapshot GetSnapshot(tx::transaction_id_t tx_id);
+  tx::Transaction *RunningTransaction(tx::transaction_id_t tx_id) override;
 
  private:
   std::atomic<transaction_id_t> counter_{0};

src/transactions/engine_worker.cpp

@@ -13,20 +13,6 @@ WorkerEngine::WorkerEngine(communication::messaging::System &system,
                            const io::network::Endpoint &endpoint)
     : rpc_client_(system, endpoint, kTransactionEngineRpc) {}
 
-Transaction *WorkerEngine::LocalBegin(transaction_id_t tx_id) {
-  auto accessor = active_.access();
-  auto found = accessor.find(tx_id);
-  if (found != accessor.end()) return found->second;
-
-  Snapshot snapshot(
-      std::move(rpc_client_.Call<SnapshotRpc>(kRpcTimeout, tx_id)->member));
-  auto insertion =
-      accessor.insert(tx_id, new Transaction(tx_id, snapshot, *this));
-  CHECK(insertion.second) << "Transaction already inserted";
-  utils::EnsureAtomicGe(local_last_, tx_id);
-  return insertion.first->second;
-}
-
 CommitLog::Info WorkerEngine::Info(transaction_id_t tid) const {
   auto info = clog_.fetch_info(tid);
   // If we don't know the transaction to be commited nor aborted, ask the
@@ -66,4 +52,18 @@ void WorkerEngine::LocalForEachActiveTransaction(
   for (auto pair : active_.access()) f(*pair.second);
 }
 
+tx::Transaction *WorkerEngine::RunningTransaction(tx::transaction_id_t tx_id) {
+  auto accessor = active_.access();
+  auto found = accessor.find(tx_id);
+  if (found != accessor.end()) return found->second;
+
+  Snapshot snapshot(
+      std::move(rpc_client_.Call<SnapshotRpc>(kRpcTimeout, tx_id)->member));
+  auto insertion =
+      accessor.insert(tx_id, new Transaction(tx_id, snapshot, *this));
+  CHECK(insertion.second) << "Transaction already inserted";
+  utils::EnsureAtomicGe(local_last_, tx_id);
+  return insertion.first->second;
+}
+
 }  // namespace tx

src/transactions/engine_worker.hpp

@@ -20,8 +20,6 @@ class WorkerEngine : public Engine {
   WorkerEngine(communication::messaging::System &system,
                const io::network::Endpoint &endpoint);
 
-  Transaction *LocalBegin(transaction_id_t tx_id);
-
   CommitLog::Info Info(transaction_id_t tid) const override;
   Snapshot GlobalGcSnapshot() override;
   Snapshot GlobalActiveTransactions() override;
@@ -29,6 +27,7 @@ class WorkerEngine : public Engine {
   tx::transaction_id_t LocalLast() const override;
   void LocalForEachActiveTransaction(
       std::function<void(Transaction &)> f) override;
+  tx::Transaction *RunningTransaction(tx::transaction_id_t tx_id) override;
 
  private:
   // Local caches.

tests/unit/transaction_engine_distributed.cpp

@@ -22,11 +22,11 @@ class WorkerEngineTest : public testing::Test {
   WorkerEngine worker_{worker_system_, master_system_.endpoint()};
 };
 
-TEST_F(WorkerEngineTest, LocalBegin) {
+TEST_F(WorkerEngineTest, RunningTransaction) {
   master_.Begin();
   master_.Begin();
-  worker_.LocalBegin(1);
-  worker_.LocalBegin(2);
+  worker_.RunningTransaction(1);
+  worker_.RunningTransaction(2);
   int count = 0;
   worker_.LocalForEachActiveTransaction([&count](Transaction &t) {
     ++count;
@@ -87,24 +87,24 @@ TEST_F(WorkerEngineTest, GlobalIsActive) {
 TEST_F(WorkerEngineTest, LocalLast) {
   master_.Begin();
   EXPECT_EQ(worker_.LocalLast(), 0);
-  worker_.LocalBegin(1);
+  worker_.RunningTransaction(1);
   EXPECT_EQ(worker_.LocalLast(), 1);
   master_.Begin();
   EXPECT_EQ(worker_.LocalLast(), 1);
   master_.Begin();
   EXPECT_EQ(worker_.LocalLast(), 1);
   master_.Begin();
-  worker_.LocalBegin(4);
+  worker_.RunningTransaction(4);
   EXPECT_EQ(worker_.LocalLast(), 4);
 }
 
 TEST_F(WorkerEngineTest, LocalForEachActiveTransaction) {
   master_.Begin();
-  worker_.LocalBegin(1);
+  worker_.RunningTransaction(1);
   master_.Begin();
   master_.Begin();
   master_.Begin();
-  worker_.LocalBegin(4);
+  worker_.RunningTransaction(4);
   std::unordered_set<tx::transaction_id_t> local;
   worker_.LocalForEachActiveTransaction(
       [&local](Transaction &t) { local.insert(t.id_); });

tests/unit/transaction_engine_single_node.cpp

@@ -63,3 +63,12 @@ TEST(Engine, ConcurrentBegin) {
   for (auto &t : threads) t.join();
   EXPECT_EQ(tx_ids.access().size(), 1000);
 }
+
+TEST(Engine, RunningTransaction) {
+  tx::SingleNodeEngine engine;
+  auto t0 = engine.Begin();
+  auto t1 = engine.Begin();
+  EXPECT_EQ(t0, engine.RunningTransaction(t0->id_));
+  EXPECT_NE(t1, engine.RunningTransaction(t0->id_));
+  EXPECT_EQ(t1, engine.RunningTransaction(t1->id_));
+}