From: Tom Lane <tgl@sss.pgh.pa.us>
To: Dmitry Dolgov <9erthalion6@gmail.com>
cc: John Naylor <john.naylor@enterprisedb.com>, tharakan@gmail.com,
        pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17774: Assert triggered on brin_minmax_multi.c
In-reply-to: <20230208153313.fym7at3ubgrec67a@ddolgov.remote.csb>
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 <20230208100658.mz2kkeruoma6iqtw@ddolgov.remote.csb>
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 <20230208153313.fym7at3ubgrec67a@ddolgov.remote.csb>
Comments: In-reply-to Dmitry Dolgov <9erthalion6@gmail.com>
	message dated "Wed, 08 Feb 2023 16:33:13 +0100"
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Date: Wed, 08 Feb 2023 11:05:16 -0500
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Dmitry Dolgov <9erthalion6@gmail.com> writes:
>> On Wed, Feb 08, 2023 at 10:03:01AM -0500, Tom Lane wrote:
>> I'd believe this argument more readily if the calculation weren't being
>> done in float arithmetic.  Since it is, you're at the mercy of roundoff
>> error ... and that small negative delta could certainly pass for
>> roundoff error.

> Hmm...yeah, good point. In both the reproducer I've posted and the
> backtrace from the thread the delta is indeed rather small.

I bet also it only fails when dealing with IPv6 addresses.
With 32-bit IPv4 addresses, a float8 would have enough mantissa
bits that the calculation wouldn't become imprecise.

			regards, tom lane