Re: Sync scan & regression tests

Heikki Linnakangas <hlinnaka(at)iki(dot)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(at)anarazel(dot)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