> You never need to reduce it to a shared lock. On postmaster startup, > try to lock the sentinel byte (one byte past the end-of-file). If you > can lock it, you know that no other postmaster has that byte locked. If > you can't lock it, another postmaster is running. It is an atomic > operation. This doesn't work if the postmaster dies but a backend continues to run, which is arguably the most important case we need to protect against.
I may be confused here, but I don't see the problem - byte-range locks are not inherited across a fork. A backend would never hold the lock, a backend would never even look for the lock.
> However, Tom may be correct about NFS locking, but I guess I'm surprised > that anyone would care :-) Quite a lot of people run NFS-mounted data directories ...
I'm happy to take your word for that, and I agree that if NFS is important and locking is brain-dead on NFS, then relying solely on a lock is unacceptable.
-- Korry
