Re: Re: [COMMITTERS] pgsql: Add some isolation tests for deadlock detection and resolution.

I wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> As for the patch itself, I'm having trouble grokking what it's trying
>> to do. I think it might be worth having a comment defining precisely
>> what we mean by "A blocks B". I would define "A blocks B" in general
>> as either A holds a lock which conflicts with one sought by B
>> (hard-blocked) or A awaits a lock which conflicts with one sought by B
>> and precedes it in the wait queue (soft-blocked).

> Yes, that is exactly what I implemented ... and it's something you can't
> find out from pg_locks. I'm not sure how that view could be made to
> expose wait-queue ordering.

Here's an updated version of this patch, now with user-facing docs.

I decided that "pg_blocking_pids()" is a better function name than
"pg_blocker_pids()". The code's otherwise the same, although I
revisited some of the comments.

I also changed quite a few references to "transaction" into "process"
in the discussion of pg_locks. The previous choice to conflate
processes with transactions was never terribly wise in my view, and
it's certainly completely broken by parallel query.

regards, tom lane