FileAlreadyExistException when writing tachyon table

currently Shark write data into Tachyon table directly by RAWTable interface in Tachyon.
when  speculation execution is on,   it throws FileAlreadyExistException because two tasks attempts to write same partition into Tachyon table
the approach to solve the problem is first write output of each task into a temp folder,  then commit the result when the task ends. just like write to HDFS.