Horton

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

John Naylor <john.naylor@2ndquadrant.com>

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From: John Naylor <john.naylor@2ndquadrant.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2019-05-03T06:12:48Z
Lists: pgsql-hackers

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On Thu, May 2, 2019 at 4:57 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Thu, May 2, 2019 at 12:39 PM John Naylor <john.naylor@2ndquadrant.com> wrote:
> >
> Okay,  I have updated the patch to incorporate your changes and call
> relcache invalidation at required places. I have updated comments at a
> few places as well.  The summarization of this patch is that (a) it
> moves the local map to relation cache (b) performs the cache
> invalidation whenever we create fsm (either via backend or vacuum),
> when some space in a page is freed by vacuum (provided fsm doesn't
> exist) or whenever the local map is cleared (c) additionally, we clear
> the local map when we found a block from FSM, when we have already
> tried all the blocks present in cache or when we are allowed to create
> FSM.
>
> If we agree on this, then we can update the README accordingly.
>
> Can you please test/review?

There isn't enough time. But since I already wrote some debugging
calls earlier (attached), I gave it a brief spin, I found this patch
isn't as careful as HEAD making sure we don't try the same block twice
in a row. If you insert enough tuples into an empty table such that we
need to extend, you get something like this:

DEBUG:  Not enough space on block 0
DEBUG:  Now trying block 0
DEBUG:  Not enough space on block 0
DEBUG:  Updating local map for block 0

At this point, I'm sorry to say, but I'm in favor of reverting. There
just wasn't enough time to redesign and debug a feature like this
during feature freeze.

-- 
John Naylor                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.