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From: Andres Freund <[email protected]>
To: Alvaro Herrera <[email protected]>
To: Tom Lane <[email protected]>
Cc: Andrew Dunstan <[email protected]>
Cc: Kuntal Ghosh <[email protected]>
Cc: Michael Paquier <[email protected]>
Cc: Tomas Vondra <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Thomas Munro <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: subscriptionCheck failures on nightjar
Date: Fri, 20 Sep 2019 15:11:22 -0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

Hi, 

On September 20, 2019 3:06:20 PM PDT, Alvaro Herrera <[email protected]> wrote:
>On 2019-Sep-20, Tom Lane wrote:
>
>> Actually, what I did was as attached [1], and I am getting traces
>like
>> [2].  The problem seems to occur only when there are two or three
>> processes concurrently creating the same snapshot file.  It's not
>> obvious from the debug trace, but the snapshot file *does* exist
>> after the music stops.
>
>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.

We try to avoid it, but the check is racy. Check comments in SnapBuildSerialize. We could introduce locking etc to avoid that, but that seems overkill, given that were really just dealing with a broken os.

Andres
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

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