Re: [ADMIN] Question about multiple postmasters

On Thu, 1 Oct 1998, Bruce Momjian wrote:

> > > > Has anyone tried running multiple postmasters w/ the same data
> > > > directory.
> > > > Any issues to watch out for? Problems with locking?
> > > > All of the systems would be running on Red Hat 5.1 x86.
> > >
> > > Hard to imagine why you would want to do that. pg_log would be shared
> > > by all backends, even if they connect to different databases, so this
> > > is
> > > very bad.
> > Where is the pg_log located? The only thing they would share would be
> > data directories. I plan on running each backing on different machines
> > sharing a data directory. It's more for load distribution than anything
> > else.
>
> It will not work. pg_log is in the toplevel data directory, and some of
> the stuff is stored in shared memory, which is not shared among
> postmasters.

I believe what he is asking is if he can use an NFS mount or some other
network based file system to house the data directory used by a few
machines thereby spreading the queries across them. Now I don't know much
about the internals but I can suggest that he be very careful... NFS is
basically stateless and it would be *REALLY* easy to screw up a data file.

Regardless his original question still stands - can it be done?

BTW replication would probably be the real solution he wants. I could see
trying to NFS mount a common disk area as a poor man's replication, but
then the reliability of the entire server array becomes focused on a
single server (the NFS master) and speed becomes based on the slowest
link- transfering huge files over NFS. Sort of defeats the purpose of an
sharing the load across a set of servers doesn't it?

Chris

--
Useless Fact #3: Donald Duck's middle name is Fauntleroy.