To facilitate the LSN check, the server maintains a table containing the LSNs of all pages that are currently cached on one or more client workstations. In all the three algorithms, client updates are performed locally, but they are not permitted to migrate back to the server until the update transaction enters its commit pahse. These clients request update-copy locks on teh updated data on behalf of the committing transactions. It is lock that enable certain deadlocks to be detected early. All the five algorithms in the above for client-server cache consistency are based on viewing cached pages as replicated data.
Server handles all lock requests.
C2PL extends B2PL to support cacing across transaction boundaries. It extends tha aggregate memory of the DBMS to include the buffer space on the client workstation. Still server handles all lock requests. O2PL extends C2PL by allowing client transactions to execute entirely locally beteen cache misses, communicating with no server interactions until they reach their commit point. All the three O2PL algorithms allow additional concurrency since they detect data conflicts later which may lead to more aborts later.