From a7f9255c17bc443ac6e573b911536dfceca853b1 Mon Sep 17 00:00:00 2001
From: Dominik Gleich <dominik.gleich@memgraph.io>
Date: Mon, 27 Nov 2017 14:57:45 +0100
Subject: [PATCH] Remove redundant transaction from index creation

Reviewers: florijan

Reviewed By: florijan

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1011
---
 src/database/graph_db_accessor.cpp | 11 +++--------
 src/transactions/engine.hpp        |  9 +++++++++
 tests/unit/durability.cpp          | 14 ++++++--------
 3 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/src/database/graph_db_accessor.cpp b/src/database/graph_db_accessor.cpp
index ebc374573..1789c7777 100644
--- a/src/database/graph_db_accessor.cpp
+++ b/src/database/graph_db_accessor.cpp
@@ -124,19 +124,14 @@ void GraphDbAccessor::BuildIndex(const GraphDbTypes::Label &label,
   // happened earlier. We have to first wait for every transaction that
   // happend before, or a bit later than CreateIndex to end.
   {
-    auto wait_transaction = db_.tx_engine_.Begin();
-    for (auto id : wait_transaction->snapshot()) {
+    auto wait_transactions = db_.tx_engine_.ActiveTransactions();
+    for (auto id : wait_transactions) {
       if (id == transaction_->id_) continue;
-      while (wait_transaction->engine_.IsActive(id)) {
+      while (db_.tx_engine_.IsActive(id)) {
         // TODO reconsider this constant, currently rule-of-thumb chosen
         std::this_thread::sleep_for(std::chrono::microseconds(100));
       }
     }
-    // We must notify the WAL about this transaction manually since it's not
-    // handled by a GraphDbAccessor.
-    db_.wal_.TxBegin(wait_transaction->id_);
-    db_.wal_.TxCommit(wait_transaction->id_);
-    wait_transaction->Commit();
   }
 
   // This accessor's transaction surely sees everything that happened before
diff --git a/src/transactions/engine.hpp b/src/transactions/engine.hpp
index 33565cf07..082de47b9 100644
--- a/src/transactions/engine.hpp
+++ b/src/transactions/engine.hpp
@@ -100,6 +100,15 @@ class Engine {
     return snapshot_copy;
   }
 
+  /**
+   * Returns active transactions.
+   */
+  Snapshot ActiveTransactions() {
+    std::lock_guard<SpinLock> guard(lock_);
+    Snapshot active_transactions = active_;
+    return active_transactions;
+  }
+
   /** Comits the given transaction. Deletes the transaction object, it's not
    * valid after this function executes. */
   void Commit(const Transaction &t) {
diff --git a/tests/unit/durability.cpp b/tests/unit/durability.cpp
index 8e23a022d..d8c033794 100644
--- a/tests/unit/durability.cpp
+++ b/tests/unit/durability.cpp
@@ -338,7 +338,7 @@ TEST_F(Durability, WalEncoding) {
     }
   }
   reader.Close();
-  ASSERT_EQ(ops.size(), 13);
+  ASSERT_EQ(ops.size(), 11);
 
   using Type = durability::WriteAheadLog::Op::Type;
   EXPECT_EQ(ops[0].type_, Type::TRANSACTION_BEGIN);
@@ -369,16 +369,14 @@ TEST_F(Durability, WalEncoding) {
   EXPECT_EQ(ops[6].edge_id_, 0);
   EXPECT_EQ(ops[6].property_, "p0");
   EXPECT_EQ(ops[6].value_.type(), PropertyValue::Type::List);
-  // The next four ops are the BuildIndex internal transactions.
+  // The next two ops are the BuildIndex internal transactions.
   EXPECT_EQ(ops[7].type_, Type::TRANSACTION_BEGIN);
   EXPECT_EQ(ops[8].type_, Type::TRANSACTION_COMMIT);
-  EXPECT_EQ(ops[9].type_, Type::TRANSACTION_BEGIN);
+  EXPECT_EQ(ops[9].type_, Type::BUILD_INDEX);
+  EXPECT_EQ(ops[9].label_, "l1");
+  EXPECT_EQ(ops[9].property_, "p1");
   EXPECT_EQ(ops[10].type_, Type::TRANSACTION_COMMIT);
-  EXPECT_EQ(ops[11].type_, Type::BUILD_INDEX);
-  EXPECT_EQ(ops[11].label_, "l1");
-  EXPECT_EQ(ops[11].property_, "p1");
-  EXPECT_EQ(ops[12].type_, Type::TRANSACTION_COMMIT);
-  EXPECT_EQ(ops[12].transaction_id_, 1);
+  EXPECT_EQ(ops[10].transaction_id_, 1);
 }
 
 TEST_F(Durability, SnapshotEncoding) {