Hi Rajat
When you say performance is slow on the system ,
I assume that you are meaning the overall SAP Performance.
There are several reasons for the same as mentioned above also in the replies :
a) At OS Level - as pointed out in the above replies
b) DB Level - during the time of the performance degradation - please check AWR / ADDM reports which will tell on its own several recommendations.
c) Application level issues - if you see long running queries in the system , then you need to go for Performance tuning
618868 FAQ: Oracle performance
In short , it requires a holistic approach for performance tuning of the overall system - unless you have some specific observations of performance degradation.
Thanks
Rishi