| From: | Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com> |
| Subject: | Re: BRIN minmax multi - incorrect distance for infinite timestamp/date |
| Date: | 2023-10-13 12:04:02 |
| Message-ID: | CAEZATCUNjgmTfTJnkR+DMXfRbrm+bqJuEZ-fKRJF3X4mr=o3LQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, 13 Oct 2023 at 11:44, Tomas Vondra
<tomas(dot)vondra(at)enterprisedb(dot)com> wrote:
>
> On 10/13/23 11:21, Dean Rasheed wrote:
> >
> > Is this only inefficient? Or can it also lead to wrong query results?
>
> I don't think it can produce incorrect results. It only affects which
> values we "merge" into an interval when building the summaries.
>
Ah, I get it now. These "distance" support functions are only used to
see how far apart 2 ranges are, for the purposes of the algorithm that
merges the 2 closest ranges. So if it gets it wrong, it only leads to
a poor choice of ranges to merge, making the query inefficient, but
still correct.
Presumably, that also makes this kind of change safe to back-patch
(not sure if you were planning to do that?), since it will only affect
range merging choices when inserting new values into existing indexes.
Regards,
Dean
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