Re: Improving backend startup interlock

Have people considered flock (advisory locking) on the postmaster.pid
file for backend detection?   It has a nonblocking option.  Don't most
OS's support it?

I can't understand why we can't get an easier solution to postmaster
detection than shared memory.

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Tom Lane wrote:
> Giles Lean <giles@nemeton.com.au> writes:
> > I'm certainly no fan of NFS locking, but if someone trusts their NFS
> > client and server implementations enough to put their data on, they
> > might as well trust it to get a single lock file for startup right
> > too.  IMHO.  Your mileage may vary.
> 
> Well, my local man page for lockf() sez
> 
>      The advisory record-locking capabilities of lockf() are implemented
>      throughout the network by the ``network lock daemon'' (see lockd(1M)).
>      If the file server crashes and is rebooted, the lock daemon attempts
>      to recover all locks associated with the crashed server.  If a lock
>      cannot be reclaimed, the process that held the lock is issued a
>      SIGLOST signal.
> 
> and the lockd man page mentions that not only lockd but statd have to be
> running locally *and* at the NFS server.
> 
> This sure sounds like file locking on NFS introduces additional
> failure modes above and beyond what we have already.
> 
> Since the entire point of this locking exercise is to improve PG's
> robustness, solutions that depend on other daemons not crashing
> don't sound like a step forward to me.  I'm willing to trust the local
> kernel, but I get antsy if I have to trust more than that.
> 
>             regards, tom lane
> 
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