Horton

Re: Sync scan & regression tests

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Andres Freund <andres@anarazel.de>, Tomas Vondra <tomas.vondra@enterprisedb.com>, David Rowley <dgrowleyml@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>, Konstantin Knizhnik <knizhnik@garret.ru>, pgsql-hackers@lists.postgresql.org, Thomas Munro <thomas.munro@gmail.com>
Date: 2023-09-18T13:45:19Z
Lists: pgsql-hackers 
Heikki Linnakangas <hlinnaka@iki.fi> writes:
> On 05/09/2023 06:16, Tom Lane wrote:
>> So chipmunk is getting through the core tests now, but instead it
>> is failing in contrib/pg_visibility [1]:

> I bisected it to this:
> commit 82a4edabd272f70d044faec8cf7fd1eab92d9991 (HEAD)
> Author: Andres Freund <andres@anarazel.de>
> Date:   Mon Aug 14 09:54:03 2023 -0700
>      hio: Take number of prior relation extensions into account

Yeah, I came to the same conclusion after discovering that I could
reproduce it locally with small shared_buffers.

> I think the behavior is fine. The reasons given in the commit message 
> make sense. But it would be nice to silence the test failure. Some 
> alternatives:
> ...
> c) Change the extension logic so that we don't extend so much when the 
> table is small. The efficiency of bulk extension doesn't matter when the 
> table is tiny, so arguably we should rather try to minimize the table 
> size. If you have millions of tiny tables, allocating one extra block on 
> each adds up.

I think your alternative (c) is plenty attractive.  IIUC, the current
change has at one stroke doubled the amount of disk space eaten by
a table that formerly needed two pages.  I don't think we should be
adding more than one page at a time until the table size reaches
perhaps 10 pages.

			regards, tom lane

Commits

  1. Avoid edge case in pg_visibility test with small shared_buffers

  2. Report syncscan position at end of scan.

  3. hio: Take number of prior relation extensions into account

  4. Reduce code duplication between heapgettup and heapgettup_pagemode

  5. Fix CLUSTER tuplesorts on abbreviated expressions.

  6. Set PD_ALL_VISIBLE and visibility map bits in COPY FREEZE