Re: file-locking and postmaster.pid

[korry <korry(at)appx(dot)com>]

> > > > 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.
>
> Well, you are wrong here.  We _want_ every backend to hold a shared
> lock.  We need to stop a postmaster from starting if there is a backend
> running that was started by a no-longer-running postmaster.

Oh... didn't know that.  How is that accomplished now? There must be some code beside the pid file check.

            -- Korry