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

On Tue, Apr 30, 2024 at 7:54 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Alexander Korotkov <aekorotkov@gmail.com> writes:
> > Given this, should we try to do better with binary compatibility
> > checks using ControlFileData?  AFAICS they are supposed to check if
> > the database cluster is binary compatible with the running
> > architecture.  But it obviously allows incompatibilities.
>
> Perhaps.  pg_control already covers endianness, which I think
> is the root of the hashing differences I showed.  Adding a field
> for char signedness feels a little weird, since it's not directly
> a property of the bits-on-disk, but maybe we should.

I agree that storing char signedness might seem weird.  But it appears
that we already store indexes that depend on char signedness.  So,
it's effectively property of bits-on-disk even though it affects
indirectly.  Then I see two options to make the picture consistent.
1) Assume that char signedness is somehow a property of bits-on-disk
even though it's weird.  Then pg_trgm indexes are correct, but we need
to store char signedness in pg_control.
2) Assume that char signedness is not a property of bits-on-disk.
Then pg_trgm indexes are buggy and need to be fixed.
What do you think?

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Regards,
Alexander Korotkov