Re: Emit fewer vacuum records by reaping removable tuples during pruning

Melanie Plageman <melanieplageman@gmail.com>

From: Melanie Plageman <melanieplageman@gmail.com>

To: Robert Haas <robertmhaas@gmail.com>

Cc: Michael Paquier <michael@paquier.xyz>, Peter Geoghegan <pg@bowt.ie>, Pg Hackers <pgsql-hackers@postgresql.org>, Andres Freund <andres@anarazel.de>

Date: 2024-01-09T22:42:38Z

Lists: pgsql-hackers

Attachments

v6-0003-Move-VM-update-code-to-lazy_scan_prune.patch (text/x-patch) patch v6-0003
v6-0001-Set-would-be-dead-items-LP_UNUSED-while-pruning.patch (text/x-patch) patch v6-0001
v6-0002-Indicate-rel-truncation-unsafe-in-lazy_scan-no-pr.patch (text/x-patch) patch v6-0002
v6-0005-Move-freespace-map-update-into-lazy_scan_-no-prun.patch (text/x-patch) patch v6-0005
v6-0004-Inline-LVPagePruneState-members-in-lazy_scan_prun.patch (text/x-patch) patch v6-0004

On Tue, Jan 9, 2024 at 3:40 PM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Tue, Jan 9, 2024 at 3:13 PM Melanie Plageman
> <melanieplageman@gmail.com> wrote:
> > I had already written the patch for immediate reaping addressing the
> > below feedback before I saw the emails that said everyone is happy
> > with using hastup in lazy_scan_[no]prune() in a preliminary patch. Let
> > me know if you have a strong preference for reordering. Otherwise, I
> > will write the three subsequent patches on top of this one.
>
> I don't know if it rises to the level of a strong preference. It's
> just a preference.

Attached v6 has the immediate reaping patch first followed by the code
to use hastup in lazy_scan_[no]prune(). 0003 and 0004 move the VM
update code into lazy_scan_prune() and eliminate LVPagePruneState
entirely. 0005 moves the FSM update into lazy_scan_[no]prune(),
substantially simplifying lazy_scan_heap().

> I agree that we can leave that out. It wouldn't be bad to include it
> if someone had a nice way of doing that, but it doesn't seem critical,
> and if forcing it in there makes the comment less clear overall, it's
> a net loss IMHO.
>
> > Hmm. Yes. I suppose I was trying to find something to validate. Is it
> > worth checking that the line pointer is not already LP_UNUSED? Or is
> > that a bit ridiculous?
>
> I think that's worthwhile (hence my proposed wording).

Done in attached v6.

- Melanie

Commits

Combine FSM updates for prune and no-prune cases.
- 5eafacd2797d 17.0 landed
Remove LVPagePruneState.
- e313a6113704 17.0 landed
Move VM update code from lazy_scan_heap() to lazy_scan_prune().
- cb970240f13d 17.0 landed
Optimize vacuuming of relations with no indexes.
- c120550edb86 17.0 landed
Be more consistent about whether to update the FSM while vacuuming.
- 45d395cd75ff 17.0 landed
Remove hastup from LVPagePruneState.
- e2d5b3b9b643 17.0 landed
Use scanned_pages to decide when to failsafe check.
- 07eef53955ea 16.0 cited
Simplify lazy_scan_heap's handling of scanned pages.
- 44fa84881fff 15.0 cited
While vacuuming a large table, update upper-level FSM data every so often.
- 851a26e26637 11.0 cited