when I am trying to export some paramters and tables in RFC function module, i m getting error as well as a warning message stating performance will reduce.
So please help me to solve the issue.
You are getting this message because you are exporting tables 'by value'. Since this will cause the complete data in that internal table to be copied into a new memory area this might impact the performance of that function in case the table has a lot of data in it.
However - for an RFC you can only define parameters to be called by value, hence this is not an error in your case. It just lets you know that the performance will suffer when you have lots of data in your internal table compared to a function that would pass the data by reference - but you don't have that option for an RFC anyway.
Hope that helps,