From 90f744941d48f15d5d070dfcab5d51b77abac8ad Mon Sep 17 00:00:00 2001
From: jsteemann <jan@arangodb.com>
Date: Fri, 17 Aug 2018 11:53:33 -0700
Subject: [PATCH] adds missing PopSavePoint method to Transaction (#4256)

Summary:
Transaction has had methods to deal with SavePoints already, but
was missing the PopSavePoint method provided by WriteBatch and
WriteBatchWithIndex.
This PR adds PopSavePoint to Transaction as well. Having the method
on Transaction-level too is useful for applications that repeatedly
execute a sequence of operations that normally succeed, but infrequently
need to get rolled back. Using SavePoints here is sensible, but as
operations normally succeed the application may pile up a lot of
useless SavePoints inside a Transaction, leading to slightly increased
memory usage for managing the unneeded SavePoints.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4256

Differential Revision: D9326932

Pulled By: yiwu-arbug

fbshipit-source-id: 53a0af18a6c7e87feff8a56f1f3eab9df7f371d6
---
 include/rocksdb/utilities/transaction.h    |  6 ++
 utilities/transactions/transaction_base.cc | 13 ++++
 utilities/transactions/transaction_base.h  |  2 +
 utilities/transactions/transaction_test.cc | 73 ++++++++++++++++++++++
 4 files changed, 94 insertions(+)

diff --git a/include/rocksdb/utilities/transaction.h b/include/rocksdb/utilities/transaction.h
index bdf918fd6c..86627d4f45 100644
--- a/include/rocksdb/utilities/transaction.h
+++ b/include/rocksdb/utilities/transaction.h
@@ -152,6 +152,12 @@ class Transaction {
   // If there is no previous call to SetSavePoint(), returns Status::NotFound()
   virtual Status RollbackToSavePoint() = 0;
 
+  // Pop the most recent save point.
+  // If there is no previous call to SetSavePoint(), Status::NotFound()
+  // will be returned.
+  // Otherwise returns Status::OK().
+  virtual Status PopSavePoint() = 0;
+
   // This function is similar to DB::Get() except it will also read pending
   // changes in this transaction.  Currently, this function will return
   // Status::MergeInProgress if the most recent write to the queried key in
diff --git a/utilities/transactions/transaction_base.cc b/utilities/transactions/transaction_base.cc
index 821913ed8d..ac459a256b 100644
--- a/utilities/transactions/transaction_base.cc
+++ b/utilities/transactions/transaction_base.cc
@@ -178,6 +178,19 @@ Status TransactionBaseImpl::RollbackToSavePoint() {
     return Status::NotFound();
   }
 }
+  
+Status TransactionBaseImpl::PopSavePoint() {
+  if (save_points_ == nullptr ||
+      save_points_->empty()) {
+    // No SavePoint yet.
+    assert(write_batch_.PopSavePoint().IsNotFound());
+    return Status::NotFound();
+  }
+
+  assert(!save_points_->empty()); 
+  save_points_->pop();
+  return write_batch_.PopSavePoint();
+}
 
 Status TransactionBaseImpl::Get(const ReadOptions& read_options,
                                 ColumnFamilyHandle* column_family,
diff --git a/utilities/transactions/transaction_base.h b/utilities/transactions/transaction_base.h
index 3facd437ee..171e13588a 100644
--- a/utilities/transactions/transaction_base.h
+++ b/utilities/transactions/transaction_base.h
@@ -45,6 +45,8 @@ class TransactionBaseImpl : public Transaction {
   void SetSavePoint() override;
 
   Status RollbackToSavePoint() override;
+  
+  Status PopSavePoint() override;
 
   using Transaction::Get;
   Status Get(const ReadOptions& options, ColumnFamilyHandle* column_family,
diff --git a/utilities/transactions/transaction_test.cc b/utilities/transactions/transaction_test.cc
index 89118e0b17..44c6e35964 100644
--- a/utilities/transactions/transaction_test.cc
+++ b/utilities/transactions/transaction_test.cc
@@ -3771,6 +3771,79 @@ TEST_P(TransactionTest, SavepointTest2) {
   delete txn2;
 }
 
+TEST_P(TransactionTest, SavepointTest3) {
+  WriteOptions write_options;
+  ReadOptions read_options;
+  TransactionOptions txn_options;
+  Status s;
+
+  txn_options.lock_timeout = 1;  // 1 ms
+  Transaction* txn1 = db->BeginTransaction(write_options, txn_options);
+  ASSERT_TRUE(txn1);
+
+  s = txn1->PopSavePoint();  // No SavePoint present
+  ASSERT_TRUE(s.IsNotFound());
+
+  s = txn1->Put("A", "");
+  ASSERT_OK(s);
+  
+  s = txn1->PopSavePoint();  // Still no SavePoint present
+  ASSERT_TRUE(s.IsNotFound());
+
+  txn1->SetSavePoint();  // 1
+
+  s = txn1->Put("A", "a");
+  ASSERT_OK(s);
+
+  s = txn1->PopSavePoint();  // Remove 1
+  ASSERT_TRUE(txn1->RollbackToSavePoint().IsNotFound()); 
+
+  // Verify that "A" is still locked 
+  Transaction* txn2 = db->BeginTransaction(write_options, txn_options);
+  ASSERT_TRUE(txn2);
+
+  s = txn2->Put("A", "a2");
+  ASSERT_TRUE(s.IsTimedOut());
+  delete txn2;
+  
+  txn1->SetSavePoint();  // 2
+
+  s = txn1->Put("B", "b");
+  ASSERT_OK(s);
+  
+  txn1->SetSavePoint();  // 3
+
+  s = txn1->Put("B", "b2");
+  ASSERT_OK(s);
+
+  ASSERT_OK(txn1->RollbackToSavePoint());  // Roll back to 2
+
+  s = txn1->PopSavePoint();
+  ASSERT_OK(s);
+  
+  s = txn1->PopSavePoint();
+  ASSERT_TRUE(s.IsNotFound());
+
+  s = txn1->Commit();
+  ASSERT_OK(s);
+  delete txn1;
+
+  std::string value;
+
+  // tnx1 should have modified "A" to "a"
+  s = db->Get(read_options, "A", &value);
+  ASSERT_OK(s);
+  ASSERT_EQ("a", value);
+  
+  // tnx1 should have set "B" to just "b"
+  s = db->Get(read_options, "B", &value);
+  ASSERT_OK(s);
+  ASSERT_EQ("b", value);
+  
+  s = db->Get(read_options, "C", &value);
+  ASSERT_TRUE(s.IsNotFound());
+}
+
 TEST_P(TransactionTest, UndoGetForUpdateTest) {
   WriteOptions write_options;
   ReadOptions read_options;