Subject: Re: Update section on NFS
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
 pgsql-docs <pgsql-docs@postgresql.org>
References: <e90f24bb-5423-6abb-58ec-501176eb4afc@2ndquadrant.com>
 <83a5bea3-57cd-e820-83eb-4a9c64082c19@joeconway.com>
 <9c9c8a4c-5d69-cdbd-60c8-442ff7906d5b@2ndquadrant.com>
From: Joe Conway <mail@joeconway.com>
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Message-ID: <950271f0-d8f3-a367-14b7-1f91e4d15e40@joeconway.com>
Date: Tue, 23 Apr 2019 10:15:12 -0400
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From: Joe Conway <mail@joeconway.com>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
 pgsql-docs <pgsql-docs@postgresql.org>
Message-ID: <950271f0-d8f3-a367-14b7-1f91e4d15e40@joeconway.com>
Subject: Re: Update section on NFS
References: <e90f24bb-5423-6abb-58ec-501176eb4afc@2ndquadrant.com>
 <83a5bea3-57cd-e820-83eb-4a9c64082c19@joeconway.com>
 <9c9c8a4c-5d69-cdbd-60c8-442ff7906d5b@2ndquadrant.com>
In-Reply-To: <9c9c8a4c-5d69-cdbd-60c8-442ff7906d5b@2ndquadrant.com>

--0Ho17WYJWDCW95224Rwa2vge3OZFKWHVT
Content-Type: text/plain; charset=utf-8
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On 4/23/19 9:47 AM, Peter Eisentraut wrote:
> On 2019-04-23 14:31, Joe Conway wrote:
>> Looks like you dropped the advice WRT the asynchronous mount option.
>> Isn't that is still relevant?
>=20
> I don't think that advice was correct.  An async mounted NFS file syste=
m
> will flush data on fsync, which is what one wants.
>=20

I don't think so. Not sure if you have an account at Red Hat, but this
ticket covers it:

https://access.redhat.com/solutions/48199

Here is the relevant part of the solution as written by Red Hat:

"Finally, note that, for writes over NFS, a subsequent commit request
from the NFS client at file close time, or at
fsync() time, will force the server to write any previously unwritten
data/metadata to the disk, and the server will not reply to the client
until this has been completed, as long as sync behavior is followed. If
async is used, the commit is essentially a no-op, since the server once
again lies to the client, telling the client that the data has been sent
to stable storage. This again exposes the client and server to data
corruption, since cached data may be discarded on the client due to its
belief that the server now has the data maintained in stable storage."

Joe

--=20
Crunchy Data - http://crunchydata.com
PostgreSQL Support for Secure Enterprises
Consulting, Training, & Open Source Development


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