| From: | "Bossart, Nathan" <bossartn(at)amazon(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>, "Jamison, Kirk" <k(dot)jamison(at)jp(dot)fujitsu(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, "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: | 2019-03-04 22:00:47 |
| Message-ID: | D0540B1C-8B95-4E1C-9F1B-8DADBFC50D55@amazon.com |
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| Lists: | pgsql-hackers |
On 3/4/19, 1:44 PM, "Andres Freund" <andres(at)anarazel(dot)de> wrote:
> On 2019-03-04 21:40:53 +0000, Bossart, Nathan wrote:
>> On 3/4/19, 12:11 PM, "Andres Freund" <andres(at)anarazel(dot)de> wrote:
>> > I'm not quite convinced this is right. There's plenty sites that
>> > practically can't use autovacuum because it might decide to vacuum the
>> > 5TB index because of 300 dead tuples in the middle of busy periods. And
>> > without an reloption that's not controllable.
>>
>> Wouldn't it be better to adjust the cost and threshold parameters or
>> to manually vacuum during quieter periods?
>
> No. (auto)vacuum is useful to reclaim space etc. It's just the
> unnecessary index cleanup that's the problem... Most of the space can
> be reclaimed after all, the item pointer ain't that big...
I see what you mean.
>> I suppose setting DISABLE_INDEX_CLEANUP on a relation during busy
>> periods could be useful if you really need to continue reclaiming
>> transaction IDs, but that seems like an easy way to accidentally never
>> vacuum indexes.
>
> Yea, I do think that's a danger. But we allow disabling autovacuum, so
> I'm not sure it matters that much... And for indexes you'd still have
> the index page-level vacuum that'd continue to work.
I think the difference here is that there isn't something like
autovacuum_freeze_max_age to force index cleanup at some point.
Granted, you can set autovacuum_freeze_max_age to 2B if you want, but
at least there's a fallback available.
Nathan
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