Re: another autovacuum scheduling thread

On Sun, Oct 12, 2025 at 07:27:10PM +1300, David Rowley wrote:
> On Sat, 11 Oct 2025 at 07:43, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> I think this is a reasonable starting point, although I'm surprised
>> that you chose to combine the sub-scores using + rather than Max.
>
> Adding up the component scores doesn't make sense to me either. That
> means you could have 0.5 for inserted tuples, 0.5 for dead tuples and,
> say 0.1 for analyze threshold, which all add up to 1.1, but neither
> component score is high enough for auto-vacuum to have to do anything
> yet. With Max(), we'd clearly see that there's nothing to do since the
> overall score isn't >= 1.0.

In v3, I switched to Max().

> Maybe the score calculation could change when the relevant age() goes
> above vacuum_failsafe_age / vacuum_multixact_failsafe_age and start
> scaling it very aggressively beyond that. There's plenty to debate,
> but at a first cut, maybe something like the following (coded in SQL
> for ease of result viewing):
>
> select xidage as "age(relfrozenxid)",case xidage::float8 <
> current_setting('vacuum_failsafe_age')::float8 when true then xidage /
> current_setting('autovacuum_freeze_max_age')::float8 else power(xidage
> / current_setting('autovacuum_freeze_max_age')::float8,xidage::float8
> / 100_000_000) end xid_age_score from
> generate_series(0,2_000_000_000,100_000_000) xidage;
>
> which gives 1e+20 for age of 2 billion. It would take quite an
> unreasonable amount of bloat to score higher than that.
>
> I guess someone might argue that we should start taking it more
> seriously before the table's relfrozenxid age gets to
> vacuum_failsafe_age. Maybe that's true. I just don't know what. In any
> case, if a table's age gets that old, then something's probably not
> configured very well and needs attention. I did think maybe we could
> keep the addressing of auto-vacuum being configured to run too slowly
> as a separate thread.

I did something similar to this in v3, although I used the *_freeze_max_age
parameters as the point to start scaling aggressively, and I simply raised
the score to the power of 10.

I've yet to do any real testing with this stuff.

--
nathan