Re: file-locking and postmaster.pid

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

> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> > Certainly on all platforms there must be *some* locking primitive.  We
> > just need to figure out the appropiate parameters to fcntl() or flock()
> > or lockf() on each.

I use lockf() (not fcntl() or flock()) on every platform other than Win32.  Of course, I may not run on every system that PostgreSQL supports.

> Quite aside from the hassle factor of needing to deal with N variants of
> the syscalls, I'm not convinced that it's guaranteed to work.  ISTR that
> for instance NFS file locking is pretty much Alice-in-Wonderland :-(
>
> Since the entire point here is to have a guaranteed bulletproof check,
> locks that work most of the time on most platforms/filesystems aren't
> gonna be an improvement.

NFS file locking may certainly be problematic.  I don't know about NFS byte-range locking.

What we currently have in place is not bulletproof.  I think holding a byte-range lock in addition to the "is there some process with the right pid?" check might be a little more bullet resistant :-)


            -- Korry