Re: pgsql: Avoid spurious deadlocks when upgrading a tuple lock

Alvaro Herrera <alvherre(at)2ndquadrant(dot)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=de87a084c0a5ac927017cd0834b33a932651cfc9
>>
>> without taking your subsequent commit that silences compiler warnings at
>> https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=3da73d6839dc47f1f47ca57974bf28e5abd9b572
>> 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