Re: Building infrastructure for B-Tree deduplication that recognizes when opclass equality is also equivalence

From: Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>
To: Antonin Houska <ah(at)cybertec(dot)at>
Cc: Anastasia Lubennikova <a(dot)lubennikova(at)postgrespro(dot)ru>, Peter Geoghegan <pg(at)bowt(dot)ie>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Building infrastructure for B-Tree deduplication that recognizes when opclass equality is also equivalence
Date: 2019-10-01 05:55:32
Message-ID: 87wodpkod2.fsf@news-spur.riddles.org.uk
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>>>>> "Antonin" == Antonin Houska <ah(at)cybertec(dot)at> writes:

>> It is set to false for numeric and float4, float8.

Antonin> Are you sure about these?

numeric values can compare equal but have different display scales (see
hash_numeric).

float4 and float8 both have representations for -0, which compares equal
to 0. (numeric technically has a representation for -0 too, but I
believe the current code carefully avoids ever generating it.)

--
Andrew (irc:RhodiumToad)

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