Re: SV: Problem with pg_notify / listen

Noah Misch <noah@leadboat.com> writes:
> ... agreed.  In general, recycling SLRU space entails three steps that shall
> not overlap:

> 1. Stop reading data in the space, regulated by some "logical tail".
> 2. Unlink files wholly within the bounds of the space.
> 3. Start writing data into the space, regulated by some "physical tail" (most
>    often called a "stop limit").

Check.

> Commit d4031d7 fixed overlap of (2) and (3).  For pg_notify, though, it
> introduced overlap of (1) and (2).  I've now checked the other SLRUs for
> similar problems, but I found nothing urgent:

Good, I was wondering if we had any similar issues elsewhere.

> I think we don't yet have the right name here, seeing QUEUE_TAIL_PAGE !=
> QUEUE_POS_PAGE(QUEUE_TAIL) sounds paradoxical, yet happens regularly.  How
> about naming it QUEUE_STOP_PAGE?

Hmm, it's not very clear what "stop" means here.  What do you think of
QUEUE_OLDEST_PAGE?

            regards, tom lane