| From: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> |
|---|---|
| To: | x4mmm(at)yandex-team(dot)ru |
| Cc: | hlinnaka(at)iki(dot)fi, me(at)komzpa(dot)net, pashkin(dot)elfe(at)gmail(dot)com, thomas(dot)munro(at)gmail(dot)com, michael(at)paquier(dot)xyz, a(dot)korotkov(at)postgrespro(dot)ru, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Yet another fast GiST build |
| Date: | 2020-09-16 09:09:03 |
| Message-ID: | 20200916.180903.1084313120859935943.horikyota.ntt@gmail.com |
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| Lists: | pgsql-hackers |
At Wed, 16 Sep 2020 12:27:09 +0500, "Andrey M. Borodin" <x4mmm(at)yandex-team(dot)ru> wrote in
> I was thinking that machine epsilon is near 1e-300, but I was
> wrong. It's actually near 1e-15.
FWIW, the mantissa of double is effectively 52+1 bits, about 15.9
digits. so 1+(1e-16) is basically indistincitve from
1+(2e-16). Actually two double precisions 1+2e-16 and 1+3e-16 are
indistinctive from each other.
> Actually, I just want to understand what changes between v18 and v19 changed on-page order of items. I look into patch diff and cannot figure it out. There are only logging changes. How this affects scan?
FWIW, I saw the same symptom by my another patch after adding a value
to POINT_TBL. (But I didn't pursue the cause further..)
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
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