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

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.

--
Álvaro Herrera https://www.2ndQuadrant.com/
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