Re: Built-in Raft replication

> On 16 Apr 2025, at 09:26, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Andrey Borodin <x4mmm(at)yandex-team(dot)ru> writes:
>> I think it's what Konstantin is proposing. To have our own Raft implementation, without dependencies.
>
> Hmm, OK. I thought that the proposal involved relying on some existing
> code, but re-reading the thread that was said nowhere. Still, that
> moves it from a large project to a really large project :-(
>
> I continue to think that it'd be best to try to implement it as
> an extension, at least up till the point of finding show-stopping
> reasons why it cannot be that.

I think I can provide some reasons why it cannot be neither extension, nor any part running within postmaster reign.

1. When joining cluster, there’s not PGDATA to run postmaster on top of it.

2. After failover, old Primary node must rejoin cluster by running pg_rewind and following timeline switch.

The system in hand must be able to manipulate with PGDATA without starting Postgres.

My question to Konstantin is Why wouldn’t you just add Raft to Patroni? Is there a reason why something like Patroni is not in core and noone rushes to get it in?
Everyone is using it, or system like it.

Best regards, Andrey Borodin.