Hi B Reddy.
You are asking a Basis question and I am not Basis guy, but I will try to answer you question.
The default configuration in an SAP system supports the smallest possible system that SAP authorizes. The parameters tell the SAP application how much resources the system can use.
The reason you didn't have the problem is QA is probably due to the fact that you were not running as large a query, ro you didn't have as many concurrent users.
For more details, go to the Basis forum and search for information on the specific parameters.
I hope this helps,
John Hawk