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Re: [ADMIN] Question about multiple postmasters

From: Chris Johnson <cmj(at)inline-design(dot)com>
To: Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us>
Cc: "Jackson, DeJuan" <djackson(at)cpsgroup(dot)com>, pgsql-admin(at)postgreSQL(dot)org
Subject: Re: [ADMIN] Question about multiple postmasters
Date: 1998-10-02 14:50:16
Message-ID: Pine.LNX.4.00.9810021043160.6162-100000@boreus.bedfo.ma.tiac.net (view raw or flat)
Thread:
Lists: pgsql-admin
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.



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