Hi Mohit
1. During the month or year end time over all system usage will be very high; all the end users are running so many reports. During that time transaction users are getting affected. For this you have to check in transaction code ST03 / ST03N to find the top 20 transactions just do the analysis and fine tune the transaction with help of ABAPer or functional consultant
2. You can check those top 20 transaction in QAS system by enable the ST12 trace check over all the ABAP & DB usage.
3. During this time don’t change any settings or parameters until with solid evidence
Regards
SS