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Re: New IndexAM API controlling index vacuum strategies

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, Andres Freund <andres@anarazel.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Noah Misch <noah@leadboat.com>
Date: 2021-04-02T03:25:06Z
Lists: pgsql-hackers 
On Thu, Apr 1, 2021 at 6:14 AM Robert Haas <robertmhaas@gmail.com> wrote:
> Without offering an opinion on this particular implementation choice,
> +1 for the idea of trying to make the table-with-indexes and the
> table-without-indexes cases work in ways that will feel similar to the
> user. Tables without indexes are probably rare in practice, but if
> some behaviors are implemented for one case and not the other, it will
> probably be confusing. One thought here is that it might help to try
> to write documentation for whatever behavior you choose. If it's hard
> to document without weasel-words, maybe it's not the best approach.

I have found a way to do this that isn't too painful, a little like
the VACUUM_FSM_EVERY_PAGES thing.

I've also found a way to further simplify the table-without-indexes
case: make it behave like a regular two-pass/has-indexes VACUUM with
regard to visibility map stuff when the page doesn't need a call to
lazy_vacuum_heap() (because there are no LP_DEAD items to set
LP_UNUSED on the page following pruning). But when it does call
lazy_vacuum_heap(), the call takes care of everything for
lazy_scan_heap(), which just continues to the next page due to
considering prunestate to have been "invalidated" by the call to
lazy_vacuum_heap(). So there is absolutely minimal special case code
for the table-without-indexes case now.

BTW I removed all of the lazy_scan_heap() utility functions from the
second patch in my working copy of the patch series. You were right
about that -- they weren't useful. We should just have the pruning
wrapper function I've called lazy_scan_prune(), not any of the others.
We only need one local variable in the lazy_vacuum_heap() that isn't
either the prune state set/returned by lazy_scan_prune(), or generic
stuff like a Buffer variable.

-- 
Peter Geoghegan

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Don't truncate heap when VACUUM's failsafe is in effect.

  2. Teach VACUUM to bypass unnecessary index vacuuming.

  3. Add wraparound failsafe to VACUUM.

  4. Truncate line pointer array during VACUUM.

  5. Remove tupgone special case from vacuumlazy.c.

  6. Refactor lazy_scan_heap() loop.

  7. Propagate parallel VACUUM's buffer access strategy.

  8. Simplify state managed by VACUUM.

  9. Notice that heap page has dead items during VACUUM.

  10. Adjust lazy_scan_heap() accounting comments.

  11. Use full 64-bit XID for checking if a deleted GiST page is old enough.

  12. Fix some problems with VACUUM (INDEX_CLEANUP FALSE).