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: Amit Kapila <amit.kapila16@gmail.com>
Cc: John Naylor <john.naylor@2ndquadrant.com>, Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2019-05-01T19:21:24Z
Lists: pgsql-hackers 
On 2019-May-01, Amit Kapila wrote:

> On Tue, Apr 30, 2019 at 7:52 PM Alvaro Herrera <alvherre@2ndquadrant.com> wrote:

> > 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,
> 
> I think you intend to say the local space map because once FSM is
> created we will send invalidation and we won't further build relcache
> entry having local space map.

Yeah, I mean the map that records free space.

> > but that seems correct.  Sounds better than keeping outdated entries
> > indicating no-space-available.
> 
> Agreed, but as mentioned in one of the above emails, I am also bit
> scared that it should not lead to many invalidation messages for small
> relations, so may be we should send the invalidation message only when
> the entire page is empty.

I don't think that's a concern, is it?  You typically won't be running
multiple vacuums per second, or even multiple vacuums per minute.

-- 
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.