Re: BRIN minmax multi - incorrect distance for infinite timestamp/date

On 10/19/23 09:04, Dean Rasheed wrote:
> On Thu, 19 Oct 2023, 05:32 Ashutosh Bapat, <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com
> <mailto:ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>> wrote:
>
> On Wed, Oct 18, 2023 at 8:23 PM Tomas Vondra
> <tomas(dot)vondra(at)enterprisedb(dot)com
> <mailto:tomas(dot)vondra(at)enterprisedb(dot)com>> wrote:
>
> >
> > I did use that many values to actually force "compaction" and
> merging of
> > points into ranges. We only keep 32 values per page range, so with 2
> > values we'll not build a range. You're right it may still trigger the
> > overflow (we probably still calculate distances, I didn't realize
> that),
> > but without the compaction we can't check the query plans.
> >
> > However, I agree 60 values may be a bit too much. And I realized
> we can
> > reduce the count quite a bit by using the values_per_range option. We
> > could set it to 8 (which is the minimum).
> >
>
> I haven't read BRIN code, except the comments in the beginning of the
> file. From what you describe it seems we will store first 32 values as
> is, but later as the number of values grow create ranges from those?
> Please point me to the relevant source code/documentation. Anyway, if
> we can reduce the number of rows we insert, that will be good.
>
>
> I don't think 60 values is excessive, but instead of listing them out by
> hand, perhaps use generate_series().
>

I tried to do that, but I ran into troubles with the "date" tests. I
needed to build values that close to the min/max values, so I did
something like

SELECT '4713-01-01 BC'::date + (i || ' days')::interval FROM
generate_series(1,10) s(i);

And then the same for the max date, but that fails because of the
date/timestamp conversion in date plus operator.

However, maybe two simple generate_series() would work ...

regards

--
Tomas Vondra
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