TransactionDB:ReinitializeTransaction

Summary: Add function to reinitialize a transaction object so that it can be reused.  This is an optimization so users can potentially avoid reallocating transaction objects.

Test Plan: added tests

Reviewers: yhchiang, kradhakrishnan, IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: jkedgar, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D53835

include/rocksdb/utilities/transaction_db.h

@@ -111,14 +111,18 @@ class TransactionDB : public StackableDB {
 
   virtual ~TransactionDB() {}
 
-  // Starts a new Transaction.  Passing set_snapshot=true has the same effect
-  // as calling Transaction::SetSnapshot().
+  // Starts a new Transaction.
   //
-  // Caller should delete the returned transaction after calling
-  // Transaction::Commit() or Transaction::Rollback().
+  // Caller is responsible for deleting the returned transaction when no
+  // longer needed.
+  //
+  // If old_txn is not null, BeginTransaction will reuse this Transaction
+  // handle instead of allocating a new one.  This is an optimization to avoid
+  // extra allocations when repeatedly creating transactions.
   virtual Transaction* BeginTransaction(
       const WriteOptions& write_options,
-      const TransactionOptions& txn_options = TransactionOptions()) = 0;
+      const TransactionOptions& txn_options = TransactionOptions(),
+      Transaction* old_txn = nullptr) = 0;
 
  protected:
   // To Create an TransactionDB, call Open()

utilities/transactions/transaction_base.cc

@@ -24,7 +24,10 @@ TransactionBaseImpl::TransactionBaseImpl(DB* db,
       start_time_(db_->GetEnv()->NowMicros()),
       write_batch_(cmp_, 0, true) {}
 
-TransactionBaseImpl::~TransactionBaseImpl() {}
+TransactionBaseImpl::~TransactionBaseImpl() {
+  // Release snapshot if snapshot is set
+  SetSnapshotInternal(nullptr);
+}
 
 void TransactionBaseImpl::Clear() {
   save_points_.reset(nullptr);
@@ -35,12 +38,22 @@ void TransactionBaseImpl::Clear() {
   num_merges_ = 0;
 }
 
+void TransactionBaseImpl::Reinitialize(const WriteOptions& write_options) {
+  Clear();
+  write_options_ = write_options;
+  start_time_ = db_->GetEnv()->NowMicros();
+}
+
 void TransactionBaseImpl::SetSnapshot() {
   assert(dynamic_cast<DBImpl*>(db_) != nullptr);
   auto db_impl = reinterpret_cast<DBImpl*>(db_);
 
   const Snapshot* snapshot = db_impl->GetSnapshotForWriteConflictBoundary();
 
+  SetSnapshotInternal(snapshot);
+}
+
+void TransactionBaseImpl::SetSnapshotInternal(const Snapshot* snapshot) {
   // Set a custom deleter for the snapshot_ SharedPtr as the snapshot needs to
   // be released, not deleted when it is no longer referenced.
   snapshot_.reset(snapshot, std::bind(&TransactionBaseImpl::ReleaseSnapshot,
@@ -493,7 +506,9 @@ WriteBatchBase* TransactionBaseImpl::GetBatchForWrite() {
 }
 
 void TransactionBaseImpl::ReleaseSnapshot(const Snapshot* snapshot, DB* db) {
-  db->ReleaseSnapshot(snapshot);
+  if (snapshot != nullptr) {
+    db->ReleaseSnapshot(snapshot);
+  }
 }
 
 void TransactionBaseImpl::UndoGetForUpdate(ColumnFamilyHandle* column_family,

utilities/transactions/transaction_base.h

@@ -32,6 +32,8 @@ class TransactionBaseImpl : public Transaction {
   // Remove pending operations queued in this transaction.
   virtual void Clear();
 
+  void Reinitialize(const WriteOptions& write_options);
+
   // Called before executing Put, Merge, Delete, and GetForUpdate.  If TryLock
   // returns non-OK, the Put/Merge/Delete/GetForUpdate will be failed.
   // untracked will be true if called from PutUntracked, DeleteUntracked, or
@@ -240,7 +242,7 @@ class TransactionBaseImpl : public Transaction {
   const Comparator* cmp_;
 
   // Stores that time the txn was constructed, in microseconds.
-  const uint64_t start_time_;
+  uint64_t start_time_;
 
   // Stores the current snapshot that was was set by SetSnapshot or null if
   // no snapshot is currently set.
@@ -306,6 +308,8 @@ class TransactionBaseImpl : public Transaction {
                  bool read_only, bool untracked = false);
 
   WriteBatchBase* GetBatchForWrite();
+
+  void SetSnapshotInternal(const Snapshot* snapshot);
 };
 
 }  // namespace rocksdb

utilities/transactions/transaction_db_impl.cc

@@ -31,10 +31,14 @@ TransactionDBImpl::TransactionDBImpl(DB* db,
                           new TransactionDBMutexFactoryImpl())) {}
 
 Transaction* TransactionDBImpl::BeginTransaction(
-    const WriteOptions& write_options, const TransactionOptions& txn_options) {
-  Transaction* txn = new TransactionImpl(this, write_options, txn_options);
-
-  return txn;
+    const WriteOptions& write_options, const TransactionOptions& txn_options,
+    Transaction* old_txn) {
+  if (old_txn != nullptr) {
+    ReinitializeTransaction(old_txn, write_options, txn_options);
+    return old_txn;
+  } else {
+    return new TransactionImpl(this, write_options, txn_options);
+  }
 }
 
 TransactionDBOptions TransactionDBImpl::ValidateTxnDBOptions(
@@ -173,7 +177,7 @@ void TransactionDBImpl::UnLock(TransactionImpl* txn, uint32_t cfh_id,
 Transaction* TransactionDBImpl::BeginInternalTransaction(
     const WriteOptions& options) {
   TransactionOptions txn_options;
-  Transaction* txn = BeginTransaction(options, txn_options);
+  Transaction* txn = BeginTransaction(options, txn_options, nullptr);
 
   assert(dynamic_cast<TransactionImpl*>(txn) != nullptr);
   auto txn_impl = reinterpret_cast<TransactionImpl*>(txn);
@@ -302,5 +306,14 @@ bool TransactionDBImpl::TryStealingExpiredTransactionLocks(
   return tx.TryStealingLocks();
 }
 
+void TransactionDBImpl::ReinitializeTransaction(
+    Transaction* txn, const WriteOptions& write_options,
+    const TransactionOptions& txn_options) {
+  assert(dynamic_cast<TransactionImpl*>(txn) != nullptr);
+  auto txn_impl = reinterpret_cast<TransactionImpl*>(txn);
+
+  txn_impl->Reinitialize(write_options, txn_options);
+}
+
 }  //  namespace rocksdb
 #endif  // ROCKSDB_LITE

utilities/transactions/transaction_db_impl.h

@@ -26,7 +26,8 @@ class TransactionDBImpl : public TransactionDB {
   ~TransactionDBImpl() {}
 
   Transaction* BeginTransaction(const WriteOptions& write_options,
-                                const TransactionOptions& txn_options) override;
+                                const TransactionOptions& txn_options,
+                                Transaction* old_txn) override;
 
   using StackableDB::Put;
   virtual Status Put(const WriteOptions& options,
@@ -78,6 +79,10 @@ class TransactionDBImpl : public TransactionDB {
   bool TryStealingExpiredTransactionLocks(TransactionID tx_id);
 
  private:
+  void ReinitializeTransaction(
+      Transaction* txn, const WriteOptions& write_options,
+      const TransactionOptions& txn_options = TransactionOptions());
+
   const TransactionDBOptions txn_db_options_;
   TransactionLockMgr lock_mgr_;
 

utilities/transactions/transaction_impl.cc

@@ -39,21 +39,34 @@ TransactionImpl::TransactionImpl(TransactionDB* txn_db,
                                  const TransactionOptions& txn_options)
     : TransactionBaseImpl(txn_db->GetBaseDB(), write_options),
       txn_db_impl_(nullptr),
-      txn_id_(GenTxnID()),
-      expiration_time_(txn_options.expiration >= 0
-                           ? start_time_ + txn_options.expiration * 1000
-                           : 0),
-      lock_timeout_(txn_options.lock_timeout * 1000),
+      txn_id_(0),
+      expiration_time_(0),
+      lock_timeout_(0),
       exec_status_(STARTED) {
   txn_db_impl_ = dynamic_cast<TransactionDBImpl*>(txn_db);
   assert(txn_db_impl_);
 
+  Initialize(txn_options);
+}
+
+void TransactionImpl::Initialize(const TransactionOptions& txn_options) {
+  txn_id_ = GenTxnID();
+
+  exec_status_ = STARTED;
+
+  lock_timeout_ = txn_options.lock_timeout * 1000;
   if (lock_timeout_ < 0) {
     // Lock timeout not set, use default
     lock_timeout_ =
         txn_db_impl_->GetTxnDBOptions().transaction_lock_timeout * 1000;
   }
 
+  if (txn_options.expiration >= 0) {
+    expiration_time_ = start_time_ + txn_options.expiration * 1000;
+  } else {
+    expiration_time_ = 0;
+  }
+
   if (txn_options.set_snapshot) {
     SetSnapshot();
   }
@@ -74,6 +87,12 @@ void TransactionImpl::Clear() {
   TransactionBaseImpl::Clear();
 }
 
+void TransactionImpl::Reinitialize(const WriteOptions& write_options,
+                                   const TransactionOptions& txn_options) {
+  TransactionBaseImpl::Reinitialize(write_options);
+  Initialize(txn_options);
+}
+
 bool TransactionImpl::IsExpired() const {
   if (expiration_time_ > 0) {
     if (db_->GetEnv()->NowMicros() >= expiration_time_) {

utilities/transactions/transaction_impl.h

@@ -38,6 +38,9 @@ class TransactionImpl : public TransactionBaseImpl {
 
   virtual ~TransactionImpl();
 
+  void Reinitialize(const WriteOptions& write_options,
+                    const TransactionOptions& txn_options);
+
   Status Commit() override;
 
   Status CommitBatch(WriteBatch* batch);
@@ -82,11 +85,11 @@ class TransactionImpl : public TransactionBaseImpl {
   static std::atomic<TransactionID> txn_id_counter_;
 
   // Unique ID for this transaction
-  const TransactionID txn_id_;
+  TransactionID txn_id_;
 
   // If non-zero, this transaction should not be committed after this time (in
   // microseconds according to Env->NowMicros())
-  const uint64_t expiration_time_;
+  uint64_t expiration_time_;
 
   // Timeout in microseconds when locking a key or -1 if there is no timeout.
   int64_t lock_timeout_;
@@ -96,6 +99,8 @@ class TransactionImpl : public TransactionBaseImpl {
 
   void Clear() override;
 
+  void Initialize(const TransactionOptions& txn_options);
+
   Status ValidateSnapshot(ColumnFamilyHandle* column_family, const Slice& key,
                           SequenceNumber prev_seqno, SequenceNumber* new_seqno);
 

utilities/transactions/transaction_test.cc

@@ -448,7 +448,6 @@ TEST_F(TransactionTest, FlushTest2) {
 
     s = txn->Delete("S");
     // Should fail after encountering a write to S in SST file
-    fprintf(stderr, "%" ROCKSDB_PRIszt " %s\n", n, s.ToString().c_str());
     ASSERT_TRUE(s.IsBusy());
 
     // Write a bunch of keys to db to force a compaction
@@ -1210,6 +1209,96 @@ TEST_F(TransactionTest, ExpiredTransaction) {
   delete txn2;
 }
 
+TEST_F(TransactionTest, ReinitializeTest) {
+  WriteOptions write_options;
+  ReadOptions read_options;
+  TransactionOptions txn_options;
+  string value;
+  Status s;
+
+  // Set txn expiration timeout to 0 microseconds (expires instantly)
+  txn_options.expiration = 0;
+  Transaction* txn1 = db->BeginTransaction(write_options, txn_options);
+
+  // Reinitialize transaction to no long expire
+  txn_options.expiration = -1;
+  db->BeginTransaction(write_options, txn_options, txn1);
+
+  s = txn1->Put("Z", "z");
+  ASSERT_OK(s);
+
+  // Should commit since not expired
+  s = txn1->Commit();
+  ASSERT_OK(s);
+
+  db->BeginTransaction(write_options, txn_options, txn1);
+
+  s = txn1->Put("Z", "zz");
+  ASSERT_OK(s);
+
+  // Reinitilize txn1 and verify that Z gets unlocked
+  db->BeginTransaction(write_options, txn_options, txn1);
+
+  Transaction* txn2 = db->BeginTransaction(write_options, txn_options, nullptr);
+  s = txn2->Put("Z", "zzz");
+  ASSERT_OK(s);
+  s = txn2->Commit();
+  ASSERT_OK(s);
+  delete txn2;
+
+  s = db->Get(read_options, "Z", &value);
+  ASSERT_OK(s);
+  ASSERT_EQ(value, "zzz");
+
+  // Verify snapshots get reinitialized correctly
+  txn1->SetSnapshot();
+  s = txn1->Put("Z", "zzzz");
+  ASSERT_OK(s);
+
+  s = txn1->Commit();
+  ASSERT_OK(s);
+
+  s = db->Get(read_options, "Z", &value);
+  ASSERT_OK(s);
+  ASSERT_EQ(value, "zzzz");
+
+  db->BeginTransaction(write_options, txn_options, txn1);
+  const Snapshot* snapshot = txn1->GetSnapshot();
+  ASSERT_TRUE(snapshot);
+
+  txn_options.set_snapshot = true;
+  db->BeginTransaction(write_options, txn_options, txn1);
+  snapshot = txn1->GetSnapshot();
+  ASSERT_TRUE(snapshot);
+
+  s = txn1->Put("Z", "a");
+  ASSERT_OK(s);
+
+  txn1->Rollback();
+
+  s = txn1->Put("Y", "y");
+  ASSERT_OK(s);
+
+  txn_options.set_snapshot = false;
+  db->BeginTransaction(write_options, txn_options, txn1);
+  snapshot = txn1->GetSnapshot();
+
+  s = txn1->Put("X", "x");
+  ASSERT_OK(s);
+
+  s = txn1->Commit();
+  ASSERT_OK(s);
+
+  s = db->Get(read_options, "Z", &value);
+  ASSERT_OK(s);
+  ASSERT_EQ(value, "zzzz");
+
+  s = db->Get(read_options, "Y", &value);
+  ASSERT_TRUE(s.IsNotFound());
+
+  delete txn1;
+}
+
 TEST_F(TransactionTest, Rollback) {
   WriteOptions write_options;
   ReadOptions read_options;