system/Database/BaseConnection.php
public function transRollback(): bool
	{
		if (! $this->transEnabled || $this->transDepth === 0)
		{
			return false;
		}
		// When transactions are nested we only begin/commit/rollback the outermost ones
		elseif ($this->transDepth > 1 || $this->_transRollback())
		{
			$this->transDepth --;
			return true;
		}

		return false;
	}
public function transRollback(): bool
	{
		if (! $this->transEnabled || $this->transDepth === 0)
		{
			return false;
		}
		// When transactions are nested we only begin/commit/rollback the outermost ones
		elseif ($this->transDepth > 1 || $this->_transRollback())
		{
			$this->transDepth --;
			return true;
		}

		return false;
	}
Rollback Transaction

@return boolean