On Wed, Oct 19, 2016 at 2:44 AM, Robert Haas <robertmh...@gmail.com> wrote:
> On Sun, Oct 16, 2016 at 3:35 PM, Jeff Janes <jeff.ja...@gmail.com> wrote:
> > On Fri, Oct 7, 2016 at 6:14 AM, Robert Haas <robertmh...@gmail.com>
> >> On Thu, Oct 6, 2016 at 8:40 PM, Jeff Janes <jeff.ja...@gmail.com>
> >> > In commit 37484ad2aacef5ec7, you changed the way that frozen tuples
> >> > represented, so that we could make freezing more aggressive without
> >> > losing
> >> > forensic evidence. But I don't think we ever did anything to actually
> >> > make
> >> > the freezing more aggressive.
> >> See 3cff1879f8d03cb729368722ca823a4bf74c0cac. The objection to doing
> >> it in other cases is that it adds write-ahead log volume which might
> >> cause its own share of problems. There might be some way of getting
> >> ahead of that, though. I think if we piggyback on an existing WAL
> >> record like XLOG_HEAP2_CLEAN or XLOG_HEAP2_VISIBLE the impact might be
> >> minimal, but I haven't been dedicated enough to try to write the
> >> patch.
> >> > When I applied the up-thread patch so that pgbench_history gets
> >> > those autovacs don't actually cause any pages to get frozen until the
> >> > wrap
> >> > around kicks in, even when all the tuples on the early pages should be
> >> > well
> >> > beyond vacuum_freeze_min_age.
> >> If the pages are already all-visible, they'll be skipped until
> >> vacuum_freeze_table_age is reached.
> > So if I set vacuum_freeze_min_age to zero, then they should become
> > all-visible and all-frozen at the same time, and avoid that problem?
> Hmm. I *think* so...
> > From the docs on vacuum_freeze_min_age: "Increasing this setting may
> > unnecessary work if the rows that would otherwise be frozen will soon be
> > modified again". How much work is that? Presumably they are already
> > marked visible, is marking them frozen too a meaningful amount of extra
> > work? Is it just the extra WAL record?
> Yeah, the extra WAL record is the main thing, I think.
Closed in 2016-11 commitfest with "returned with feedback" status as per my
understanding from the recent mails on the thread.
Please feel free to change the status if the current status is doesn't