Anand,
Archiving is the logical solution for large EBAN tables. Now that your EBAN is so big, you have no other alternative. Once you implement regular archiving, other solutions become less important.
Some options to reduce the number of new purchase reqs being created:
1. Net change planning in CTM
2. Reduce CTM planning horizon
3. Use lot sizing that reduces number of PurReqs required.
Each of these options can have side effects, testing required!
Best Regards,
DB49