Program performance

Hi,

I am running the program XYZ in Background.It takes me 30 minutes to get the output.Whne i run the program second time but with the diffrent selection parameters,it only takes 3 minutes to complete the program.

the data content selected for the program is same.The program accesses the data from 2 tables which doesnot have index.

Kindly help me finding out the reason for the same.

kanishak