Message-ID: <75de1895-3bd9-242e-cf13-3f5b0281e676@enterprisedb.com>
Date: Fri, 13 Oct 2023 14:17:30 +0200
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Subject: Re: BRIN minmax multi - incorrect distance for infinite
 timestamp/date
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To: Dean Rasheed <dean.a.rasheed@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
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On 10/13/23 14:04, Dean Rasheed wrote:
> On Fri, 13 Oct 2023 at 11:44, Tomas Vondra
> <tomas.vondra@enterprisedb.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.
> 

Right.

> 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.
> 

I do plan to backpatch this, yes. I don't think there are many people
affected by this (few people are using infinite dates/timestamps, but
maybe the overflow could be more common).


regards

-- 
Tomas Vondra
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