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Re: New IndexAM API controlling index vacuum strategies

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Robert Haas <robertmhaas@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Noah Misch <noah@leadboat.com>
Date: 2021-03-15T23:16:16Z
Lists: pgsql-hackers 
Hi,

On 2021-03-15 13:58:02 -0700, Peter Geoghegan wrote:
> On Mon, Mar 15, 2021 at 12:58 PM Peter Geoghegan <pg@bowt.ie> wrote:
> > > I'm not comfortable with this change without adding more safety
> > > checks. If there's ever a case in which the HEAPTUPLE_DEAD case is hit
> > > and the xid needs to be frozen, we'll either cause errors or
> > > corruption. Yes, that's already the case with params->index_cleanup ==
> > > DISABLED, but that's not that widely used.
> >
> > I noticed that Noah's similar 2013 patch [1] added a defensive
> > heap_tuple_needs_freeze() + elog(ERROR) to the HEAPTUPLE_DEAD case. I
> > suppose that that's roughly what you have in mind here?
> 
> I'm not sure if you're arguing that there might be (either now or in
> the future) a legitimate case (a case not involving data corruption)
> where we hit HEAPTUPLE_DEAD, and find we have an XID in the tuple that
> needs freezing. You seem to be suggesting that even throwing an error
> might not be acceptable, but what better alternative is there? Did you
> just mean that we should throw a *better*, more specific error right
> there, when we handle HEAPTUPLE_DEAD? (As opposed to relying on
> heap_prepare_freeze_tuple() to error out instead, which is what would
> happen today.)

Right now (outside of the index-cleanup-disabled path), we very well may
just actually successfully and correctly do the deletion? So there
clearly is another option?

See my email from a few minutes ago for a somewhat crude idea for how to
tackle the issue differently...

Greetings,

Andres Freund

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).