Horton

Re: Unhappy about API changes in the no-fsm-for-small-rels patch

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: John Naylor <john.naylor@2ndquadrant.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2019-04-30T14:22:28Z
Lists: pgsql-hackers 
On 2019-Apr-30, John Naylor wrote:

> On Fri, Apr 26, 2019 at 11:52 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > As discussed above, we need to issue an
> > invalidation for following points:  (a) when vacuum finds there is no
> > FSM and page has more space now, I think you can detect this in
> > RecordPageWithFreeSpace
> 
> I took a brief look and we'd have to know how much space was there
> before. That doesn't seem possible without first implementing the idea
> to save free space locally in the same way the FSM does. Even if we
> have consensus on that, there's no code for it, and we're running out
> of time.

Hmm ... so, if vacuum runs and frees up any space from any of the pages,
then it should send out an invalidation -- it doesn't matter what the
FSM had, just that there is more free space now.  That means every other
process will need to determine a fresh FSM, but that seems correct.
Sounds better than keeping outdated entries indicating no-space-available.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. Revert "Avoid the creation of the free space map for small heap relations".

  2. Improve code comments in b0eaa4c51b.

  3. During pg_upgrade, conditionally skip transfer of FSMs.

  4. Add more tests for FSM.

  5. Fix typos in commit 8586bf7ed8.

  6. tableam: introduce table AM infrastructure.

  7. Clear the local map when not used.

  8. Doc: Update the documentation for FSM behavior for small tables.

  9. Make FSM test portable.

  10. Avoid creation of the free space map for small heap relations, take 2.