Re: When do vacuumed pages/tuples become available for reuse?

On Thu, Apr 11, 2019 at 1:30 PM Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
wrote:

> On 2019-Apr-11, Tom Lane wrote:
>
> > Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> > > On 2019-Apr-11, rihad wrote:
> > >> 2019-04-11 19:39:44.450844500 tuples: 19150 removed, 2725811
> remain, 465 are dead but not yet removable
> >
> > > What Jeff said. This vacuum spent a lot of time, only to remove
> miserly
> > > 19k tuples, but 2.7M dead tuples remained ... probably because you have
> > > long-running transactions preventing vacuum from removing them.
> >
> > I think you misread it --- I'm pretty sure "N remain" is referring
> > to live tuples. Maybe we should adjust the wording to make that
> > clearer?
>
> Oh, I've been confused with that many times, Not good trying to decode
> confusing messages while simultaneously figuring out trying to figure
> out logical decoding bugs that have already been fixed :-(
>
> Yeah, let's reword that. I've had to read the source half a dozen times
> because I always forget what each number means.
>

The fact that the output of "vacuum verbose" and
"log_autovacuum_min_duration" look so little like each other certainly
doesn't help us learn what they mean here. If we are re-wording things, we
might want to take a stab at unifying those to some extent. If we just
want to do a slight re-wording, I don't know what it would need to look
like. "remain" includes live, recently dead, and uncommitted new, and
uncommitted old (I think) so we can't just change "recent" to "live".

Cheers,

Jeff