| From: | Michael Paquier <michael(at)paquier(dot)xyz> |
|---|---|
| To: | Julien Rouhaud <rjuju123(at)gmail(dot)com> |
| Cc: | "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>, "Jamison, Kirk" <k(dot)jamison(at)jp(dot)fujitsu(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: reloption to prevent VACUUM from truncating empty pages at the end of relation |
| Date: | 2019-02-25 09:25:07 |
| Message-ID: | 20190225092507.GG30864@paquier.xyz |
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| Lists: | pgsql-hackers |
On Mon, Feb 25, 2019 at 08:47:28AM +0100, Julien Rouhaud wrote:
> 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.
Also, shouldn't the relopt check happen in
should_attempt_truncation()? It seems to me that if we use this
routine somewhere else then it should be controlled by the option.
At the same time, we also have REL_TRUNCATE_FRACTION and
REL_TRUNCATE_MINIMUM which could be made equally user-tunnable.
That's more difficult to control, still why don't we also consider
this part?
Another thing that seems worth thinking about is a system-level GUC,
and an option in the VACUUM command to control if truncation should
happen or not. We have a lot of infrastructure to control such
options between vacuum and autovacuum, so it could be a waste to not
consider potential synergies.
--
Michael
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