From: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
Subject: Re: subscriptionCheck failures on nightjar
To: Tom Lane <tgl@sss.pgh.pa.us>, Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Andres Freund <andres@anarazel.de>,
 Kuntal Ghosh <kuntalghosh.2007@gmail.com>,
 Michael Paquier <michael@paquier.xyz>,
 Tomas Vondra <tomas.vondra@2ndquadrant.com>,
 Robert Haas <robertmhaas@gmail.com>,
 Thomas Munro <thomas.munro@enterprisedb.com>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
References: <20190920220620.GA5214@alvherre.pgsql>
 <4218.1569017822@sss.pgh.pa.us>
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Message-ID: <31bbae1d-1670-df3b-76e6-2e8ff8e66642@2ndQuadrant.com>
Date: Mon, 23 Sep 2019 16:12:45 -0400
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On 9/20/19 6:17 PM, Tom Lane wrote:
> Alvaro Herrera <alvherre@2ndquadrant.com> writes:
>> Uh .. I didn't think it was possible that we would build the same
>> snapshot file more than once.  Isn't that a waste of time anyway?  Maybe
>> we can fix the symptom by just not doing that in the first place?
>> I don't have a strategy to do that, but seems worth considering before
>> retiring the bf animals.
> The comment near the head of SnapBuildSerialize says
>
>      * there is an obvious race condition here between the time we stat(2) the
>      * file and us writing the file. But we rename the file into place
>      * atomically and all files created need to contain the same data anyway,
>      * so this is perfectly fine, although a bit of a resource waste. Locking
>      * seems like pointless complication.
>
> which seems like a reasonable argument.  Also, this is hardly the only
> place where we expect rename(2) to be atomic.  So I tend to agree with
> Andres that we should consider OSes with such a bug to be unsupported.
>
> Dromedary is running the last release of macOS that supports 32-bit
> hardware, so if we decide to kick that to the curb, I'd either shut
> down the box or put some newer Linux or BSD variant on it.
>
> 			


Well, nightjar is on FBSD 9.0 which is oldish. I can replace it before
long with an 11-stable instance if that's appropriate.


cheers


andrew

-- 
Andrew Dunstan                https://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services