Hi,
If you refer to performance improvement in the portal, then there are few documents that were released by SAP, which can help (use to the one matching to your portal version):
Performance Best Practices Guide for SAP NetWeaver Portal 7.0
Performance Best Practices Guide for SAP NetWeaver Portal 7.3
SAP NetWeaver Portal 7.3 – Tuning Caches
This documentation is correct for all versions, and is related to Portal Activity Report that should be disabled if not needed:
Portal performance recommendations for the Portal Activity Report - Portal - SCN Wiki
I hope this information helps,
Thanks & regards,
Michal Zilcha-Lang