Shared Disk System
Use version number on the page and in the lock
When setting the lock, a process tells the lock manager its cached version number. After update, flush the page to server and increment version number in the lock.
- Can cache a page in two processes that write-lock different records
- Only one process at a time can have write privilege
- Use a global lock manager
- When setting a write lock on P, may need to refresh the cached copy from disk (if another process recently updated it)