Re: NFS, file system cache and shared_buffers

On 5/27/2014 9:09 AM, Shaun Thomas wrote:
> On 05/27/2014 10:00 AM, Albe Laurenz wrote:
>
>> I know that Oracle recommends it - they even built an NFS client
>> into their database server to make the most of it.
>
> That's odd. Every time the subject of NFS comes up, it's almost
> immediately shot down with explicit advice to Never Do That(tm). It
> can be kinda safe-ish if mounted in sync mode with caching disabled,
> but I'd never use it on any of our systems.

It has been a long time since I was in the weeds of this issue, but the
crux is that it was (still is?) hard to be sure that the filesystem's
behavior was exactly as expected. My recollection of the Oracle story
was that they had to verify the end-to-end behavior, and essentially
certify its correctness to guarantee database acid. So you needed to be
running a very specific version of the NFS code, configured in a very
specific way. This isn't entirely inconsistent with the reference above
that they "built an NFS client". That's something you might need to do
in order to be sure it behaves in the way you expect. Possibly the NFS
implementations deployed today are more consistent and correct than was
the case in the past. I wouldn't use a network filesystem for any kind
of database storage myself though.