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help / color / mirror / Atom feedFrom: Tom Lane <tgl@sss.pgh.pa.us>
To: Dean Rasheed <dean.a.rasheed@gmail.com>
Cc: Oleg Ivanov <o15611@gmail.com>
Cc: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #19340: Wrong result from CORR() function
Date: Sat, 06 Dec 2025 01:09:36 -0500
Message-ID: <2107637.1765001376@sss.pgh.pa.us> (raw)
In-Reply-To: <1872685.1764973053@sss.pgh.pa.us>
References: <19340-6fb9f6637f562092@postgresql.org>
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<375068.1764696127@sss.pgh.pa.us>
<CAEZATCU8rnyKN3z_5-osk3Bn8dtzWf9nKjTr2E16-ExXiESNrQ@mail.gmail.com>
<434484.1764707203@sss.pgh.pa.us>
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<1872685.1764973053@sss.pgh.pa.us>
I wrote:
> Dean Rasheed <dean.a.rasheed@gmail.com> writes:
>> Looking at float8_regr_accum(), I think it would be preferable to
>> arrange for it to leave Sxx, Syy, and Sxy zero until distinct X and Y
>> values are seen. I.e., something like this:
> That seems like a good idea. I was initially worried that the extra
> isnan() checks would slow down aggregation noticeably in the normal
> case where we soon discover that the inputs aren't all equal.
BTW, re-reading the patch, I now think we should drop the initial
if (isnan(commonX) || isnan(commonY))
test, instead bulling ahead with computing tmpX/tmpY/scale, and
only skip the updates of Sxx/Syy/Sxy when we have constant inputs.
Using that initial test is optimizing for constant inputs at the
expense of non-constant inputs, which seems like the wrong way
to bet.
regards, tom lane
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To: pgsql-bugs@postgresql.org
Cc: tgl@sss.pgh.pa.us, dean.a.rasheed@gmail.com, o15611@gmail.com, laurenz.albe@cybertec.at, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #19340: Wrong result from CORR() function
In-Reply-To: <2107637.1765001376@sss.pgh.pa.us>
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