Horton

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

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Melanie Plageman <melanieplageman@gmail.com>
Cc: Peter Geoghegan <pg@bowt.ie>, Michael Paquier <michael@paquier.xyz>, Pg Hackers <pgsql-hackers@postgresql.org>, Andres Freund <andres@anarazel.de>
Date: 2024-01-12T19:32:13Z
Lists: pgsql-hackers

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On Fri, Jan 12, 2024 at 1:52 PM Melanie Plageman
<melanieplageman@gmail.com> wrote:
> Yes, I was mixing the two together.
>
> I just want to make sure that we agree that, on master, when
> lazy_scan_prune() is called, the logic for whether or not to update
> the FSM after the first pass is:
>
> indexes == 0 || !has_lpdead_items || !index_vacuuming
>
> and when lazy_scan_noprune() is called, the logic for whether or not
> to update the FSM after the first pass is:
>
> indexes == 0 || !has_lpdead_items
>
> Those seem different to me.

This analysis seems correct to me, except that "when
lazy_scan_noprune() is called" should really say "when
lazy_scan_noprune() is called (and returns true)", because when it
returns false we fall through and call lazy_scan_prune() afterwards.

Here's a draft patch to clean up the inconsistency here. It also gets
rid of recordfreespace, because ISTM that recordfreespace is adding to
the confusion here rather than helping anything.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

Commits

  1. Combine FSM updates for prune and no-prune cases.

  2. Remove LVPagePruneState.

  3. Move VM update code from lazy_scan_heap() to lazy_scan_prune().

  4. Optimize vacuuming of relations with no indexes.

  5. Be more consistent about whether to update the FSM while vacuuming.

  6. Remove hastup from LVPagePruneState.

  7. Use scanned_pages to decide when to failsafe check.

  8. Simplify lazy_scan_heap's handling of scanned pages.

  9. While vacuuming a large table, update upper-level FSM data every so often.