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Re: Tablespaces and NFS

From: "Peter Koczan" <pjkoczan(at)gmail(dot)com>
To: "Carlos Moreno" <moreno_pg(at)mochima(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Tablespaces and NFS
Date: 2007-09-19 21:54:22
Message-ID: 4544e0330709191454x2b125cc0j40c57977a0106cb4@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On 9/19/07, Carlos Moreno <moreno_pg(at)mochima(dot)com> wrote:
> Hi,
>
> Anyone has tried a setup combining tablespaces with NFS-mounted partitions?
>
> I'm considering the idea as a performance-booster --- our problem is
> that we are
> renting our dedicated server from a hoster that does not offer much
> flexibility
> in terms of custom hardware configuration;  so, the *ideal* alternative
> to load
> the machine with 4 or 6 hard drives and use tablespaces is off the table
> (no pun
> intended).
>
> We could, however, set up a few additional servers where we could configure
> NFS shares, mount them on the main PostgreSQL server, and configure
> tablespaces to "load balance" the access to disk.
>
> Would you estimate that this will indeed boost performance??  (our system
> does lots of writing to DB --- in all forms:  inserts, updates, and deletes)
>
> As a corollary question:  what about the WALs and tablespaces??  Are the
> WALs "distributed" when we setup a tablespace and create tables in it?
> (that is, are the WALs corresponding to the tables in a tablespace stored
> in the directory corresponding to the tablespace?  Or is it only the
> data, and
> the WAL keeps being the one and only?)
>
> Thanks,
>
> Carlos

About 5 months ago, I did an experiment serving tablespaces out of
AFS, another shared file system.

You can read my full post at
http://archives.postgresql.org/pgsql-admin/2007-04/msg00188.php

On the whole, you're not going to see a performance improvement
running tablespaces on NFS (unless the disk system on the NFS server
is a lot faster) since you have to go through the network as well as
NFS, both of which add overhead.

Usually, locking mechanisms on shared file systems don't play nice
with databases. You're better off using something else to load balance
or replicate data.

Peter

P.S. Why not just set up those servers you're planning on using as NFS
shares as your postgres server(s)?

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