From: Oleksii Kliukin <alexk@hintbits.com>
To: Álvaro Herrera <alvherre@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: pgsql: Avoid spurious deadlocks when upgrading a tuple lock
Date: Wed, 19 Jun 2019 15:08:31 +0100
Message-ID: <2A0C6E60-661D-47BB-888C-F557D4E7458A@hintbits.com> (raw)
In-Reply-To: <20190618222547.GA18769@alvherre.pgsql>
References: <20190618222547.GA18769@alvherre.pgsql>
Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> On 2019-Jun-18, Oleksii Kliukin wrote:
>
>> Sorry, I was confused, as I was looking only at
>> https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=de87a084c0a5ac927017cd0834b33a932...
>>
>> without taking your subsequent commit that silences compiler warnings at
>> https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=3da73d6839dc47f1f47ca57974bf28e5a...
>> into consideration. With that commit, the danger is indeed in resetting the
>> skip mechanism on each jump and potentially causing deadlocks.
>
> Yeah, I understand the confusion.
>
> Anyway, as bugs go, this one seems pretty benign. It would result in a
> unexplained deadlock, very rarely, and only for people who use a very
> strange locking pattern that includes (row-level) lock upgrades. I
> think it also requires aborted savepoints too, though I don't rule out
> the possibility that there might be a way to reproduce this without
> that.
>
> I pushed the patch again just now, with the new permutation.
Thank you very much for working on it and committing the fix!
Cheers,
Oleksii
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Cc: alexk@hintbits.com, alvherre@2ndquadrant.com, tgl@sss.pgh.pa.us, pgsql-hackers@lists.postgresql.org
Subject: Re: pgsql: Avoid spurious deadlocks when upgrading a tuple lock
In-Reply-To: <2A0C6E60-661D-47BB-888C-F557D4E7458A@hintbits.com>
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