C++ Transaction::Rollback方法代码示例

void LogCache::DeleteOldRounds(uint64_t paxosID)
{
	Cursor			cursor;
	ByteArray<128>	buf;
	DynArray<128>	key;
	DynArray<128>	value;
	Transaction*	transaction;
	
	transaction = RLOG->GetTransaction();
	
	transaction->Begin();
	
	WriteRoundID(buf, paxosID);
	table->Iterate(transaction, cursor);
	if (!cursor.Start(buf))
	{
		cursor.Close();
		transaction->Rollback();
		return;
	}
		
	while (cursor.Prev(key, value))
	{
		if (key.length > sizeof("@@pround:") - 1 &&
		strncmp(key.buffer, "@@pround:", sizeof("@@pround:") - 1) == 0)
			cursor.Delete();
		else
			break;
	}
	
	cursor.Close();

	transaction->Commit();
}

int main() {
  // open DB
  Options options;
  TransactionDBOptions txn_db_options;
  options.create_if_missing = true;
  TransactionDB* txn_db;

  Status s = TransactionDB::Open(options, txn_db_options, kDBPath, &txn_db);
  assert(s.ok());

  WriteOptions write_options;
  ReadOptions read_options;
  TransactionOptions txn_options;
  std::string value;

  ////////////////////////////////////////////////////////
  //
  // Simple Transaction Example ("Read Committed")
  //
  ////////////////////////////////////////////////////////

  // Start a transaction
  Transaction* txn = txn_db->BeginTransaction(write_options);
  assert(txn);

  // Read a key in this transaction
  s = txn->Get(read_options, "abc", &value);
  assert(s.IsNotFound());

  // Write a key in this transaction
  s = txn->Put("abc", "def");
  assert(s.ok());

  // Read a key OUTSIDE this transaction. Does not affect txn.
  s = txn_db->Get(read_options, "abc", &value);

  // Write a key OUTSIDE of this transaction.
  // Does not affect txn since this is an unrelated key.  If we wrote key 'abc'
  // here, the transaction would fail to commit.
  s = txn_db->Put(write_options, "xyz", "zzz");

  // Commit transaction
  s = txn->Commit();
  assert(s.ok());
  delete txn;

  ////////////////////////////////////////////////////////
  //
  // "Repeatable Read" (Snapshot Isolation) Example
  //   -- Using a single Snapshot
  //
  ////////////////////////////////////////////////////////

  // Set a snapshot at start of transaction by setting set_snapshot=true
  txn_options.set_snapshot = true;
  txn = txn_db->BeginTransaction(write_options, txn_options);

  const Snapshot* snapshot = txn->GetSnapshot();

  // Write a key OUTSIDE of transaction
  s = txn_db->Put(write_options, "abc", "xyz");
  assert(s.ok());

  // Attempt to read a key using the snapshot.  This will fail since
  // the previous write outside this txn conflicts with this read.
  read_options.snapshot = snapshot;
  s = txn->GetForUpdate(read_options, "abc", &value);
  assert(s.IsBusy());

  txn->Rollback();

  delete txn;
  // Clear snapshot from read options since it is no longer valid
  read_options.snapshot = nullptr;
  snapshot = nullptr;

  ////////////////////////////////////////////////////////
  //
  // "Read Committed" (Monotonic Atomic Views) Example
  //   --Using multiple Snapshots
  //
  ////////////////////////////////////////////////////////

  // In this example, we set the snapshot multiple times.  This is probably
  // only necessary if you have very strict isolation requirements to
  // implement.

  // Set a snapshot at start of transaction
  txn_options.set_snapshot = true;
  txn = txn_db->BeginTransaction(write_options, txn_options);

  // Do some reads and writes to key "x"
  read_options.snapshot = txn_db->GetSnapshot();
  s = txn->Get(read_options, "x", &value);
  txn->Put("x", "x");

  // Do a write outside of the transaction to key "y"
  s = txn_db->Put(write_options, "y", "y");

  // Set a new snapshot in the transaction
//.........这里部分代码省略.........