Re: Multiple backends on a single physical database

Chris Miles <chris_pg002@psychofx.com> writes:
> On Sat, Oct 12, 2002 at 11:11:53AM -0400, Bruce Momjian wrote:
>> Good question.  It is my understanding that fsync, locking, and the
>> order of writes is not guaranteed in NFS like it is for local file
>> systems.  I question how well it would handle any of the failure modes
>> that local file systems can withstand.

AFAIR, we do not use file locking, so the unreliability of NFS locks
doesn't hurt us.  What I'd be concerned about is fsync() and sync()
semantics, namely whether data is down to disk when we think it is.

> Nobody is going to make such a guarantee with postgresql (are they?)
> so consider us a case study for such a setup.  So far, so good, even
> under heavy load testing.

Load testing is not the issue here; crash testing is.  Try pulling the
power plug on your NFS box while the database is under load.  If you
can do that repeatedly and not suffer database corruption, then maybe
you have a safe setup.  Be sure to try the case of NFS crash immediately
after a CHECKPOINT.

            regards, tom lane