Re: reloption to prevent VACUUM from truncating empty pages at theend of relation

On Mon, Feb 25, 2019 at 7:56 AM Michael Paquier <michael@paquier.xyz> wrote:
>
> On Mon, Feb 25, 2019 at 02:38:05AM +0000, Tsunakawa, Takayuki wrote:
> > From: Julien Rouhaud [mailto:rjuju123@gmail.com]
> >> One last thing, I think we should at least add one regression test for
> >> this setting.  The one you provided previously seems perfectly suited.
> >
> > Thanks, added.
>
> +SELECT pg_relation_size('reloptions_test');
> + pg_relation_size
> +------------------
> +             8192
> +(1 row)
> This makes the test page-size sensitive.  While we don't ensure that
> tests can be run with different page sizes, we should make a maximum
> effort to keep the tests compatible if that's easy enough.  In this
> case you could just use > 0 as base comparison.  I can fix that by
> myself, so no need to send a new version.

Ah good point.  We could also use something like
pg_relation_size('reloptions_test') /
current_setting('block_size')::bigint but >0 should be enough for this
test.

> Should we also document that the parameter is effective for
> autovacuum?  The name can lead to confusion regarding that.

+1