Hi Shankar,
Most of the questions should be answered by below links. Go through the same and let us know if still not answered.
Locking in Demand Planning - Technical Aspects of Demand Planning - SAP Library
Locking in Supply Network Planning (SNP) - Planning Area Administration - SAP Library
Live Cache 7.7 Parameters Tuning and Locking Issue | SCN
Meanwhile cross check other posts on SCN for the same and let us know if it worked.
Regards
Rahul