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Re: New IndexAM API controlling index vacuum strategies

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Andres Freund <andres@anarazel.de>, Masahiko Sawada <sawada.mshk@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Noah Misch <noah@leadboat.com>
Date: 2021-04-15T00:08:10Z
Lists: pgsql-hackers 
On Wed, Apr 14, 2021 at 5:55 PM Peter Geoghegan <pg@bowt.ie> wrote:
> On Wed, Apr 14, 2021 at 12:33 PM Andres Freund <andres@anarazel.de> wrote:
> > I'm getting a bit bothered by the speed at which you're pushing fairly
> > substantial behavioural for vacuum. In this case without even a warning
> > that you're about to do so.
>
> To a large degree the failsafe is something that is written in the
> hope that it will never be needed. This is unlike most other things,
> and has its own unique risks.
>
> I think that the proper thing to do is to accept a certain amount of
> risk in this area. The previous status quo was *appalling*, and so it
> seems very unlikely that the failsafe hasn't mostly eliminated a lot
> of risk for users. That factor is not everything, but it should count
> for a lot. The only way that we're going to have total confidence in
> anything like this is through the experience of it mostly working over
> several releases.

I think this is largely missing the point Andres was making, which is
that you made a significant behavior change after feature freeze
without any real opportunity for discussion. More generally, you've
changed a bunch of other stuff relatively quickly based on input from
a relatively limited number of people. Now, it's fair to say that it's
often hard to get input on things, and sometimes you have to just take
your best shot and hope you're right. But in this particular case, you
didn't even try to get broader participation or buy-in. That's not
good.

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

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).