Horton

Re: pg_trgm comparison bug on cross-architecture replication due to different char implementation

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Noah Misch <noah@leadboat.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, Joe Conway <mail@joeconway.com>, Peter Eisentraut <peter@eisentraut.org>, Alexander Korotkov <aekorotkov@gmail.com>, "Guo, Adam" <adamguo@amazon.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, Nathan Bossart <nathandbossart@gmail.com>, Jim Mlodgenski <jimmy76@gmail.com>
Date: 2024-10-02T03:57:42Z
Lists: pgsql-hackers 
Noah Misch <noah@leadboat.com> writes:
> On Tue, Oct 01, 2024 at 11:55:48AM -0700, Masahiko Sawada wrote:
>> Considering that the population of database cluster signedness will
>> converge to signedness=true in the future, we can consider using
>> -fsigned-char to prevent similar problems for the future. We need to
>> think about possible side-effects as well, though.

> It's good to think about -fsigned-char.  While I find it tempting, several
> things would need to hold for us to benefit from it:

> - Every supported compiler has to offer it or an equivalent.
> - The non-compiler parts of every supported C implementation need to
>   cooperate.  For example, CHAR_MIN must change in response to the flag.  See
>   the first comment in cash_in().
> - Libraries we depend on can't do anything incompatible with it.

> Given that, I would lean toward not using -fsigned-char.  It's unlikely all
> three things will hold.  Even if they do, the benefit is not large.

I am very, very strongly against deciding that Postgres will only
support one setting of char signedness.  It's a step on the way to
hardware monoculture, and we know where that eventually leads.
(In other words, I categorically reject Sawada-san's assertion
that signed chars will become universal.  I'd reject the opposite
assertion as well.)

			regards, tom lane

Commits

  1. pg_upgrade: Check for the expected error message in TAP tests.

  2. Fix a typo in 005_char_signedness.pl test.

  3. Add test 005_char_signedness.pl to meson.build.

  4. Fix an issue with index scan using pg_trgm due to char signedness on different architectures.

  5. pg_upgrade: Add --set-char-signedness to set the default char signedness of new cluster.

  6. pg_upgrade: Preserve default char signedness value from old cluster.

  7. pg_resetwal: Add --char-signedness option to change the default char signedness.

  8. Add default_char_signedness field to ControlFileData.

  9. Remove unneeded nbtree array preprocessing assert.