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: 2024-01-12T20:22:16Z
Lists: pgsql-hackers 
On Fri, Jan 12, 2024 at 3:04 PM Melanie Plageman
<melanieplageman@gmail.com> wrote:
> Also, I think you should combine these in lazy_scan_noprune() now
>
>     /* Save any LP_DEAD items found on the page in dead_items array */
>     if (vacrel->nindexes == 0)
>     {
>         /* Using one-pass strategy (since table has no indexes) */
>         if (lpdead_items > 0)
>         {
>
> Since we don't set recordfreespace in the outer if statement anymore

Well, maybe, but there's an else clause attached to the outer "if", so
you have to be a bit careful. I didn't think it was critical to
further rejigger this.

> And I noticed you missed a reference to recordfreespace output
> parameter in the function comment above lazy_scan_noprune().

OK.

So what's the best way to solve the problem that Peter pointed out?
Should we pass in the prunestate? Maybe just replace bool
*recordfreespace with bool *has_lpdead_items?

-- 
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.