Re: [Proposal] Fully WAL logged CREATE DATABASE - No Checkpoints

On Fri, Sep 3, 2021 at 5:54 PM Andres Freund <andres@anarazel.de> wrote:
> > I think we already have such a code in multiple places where we bypass the
> > shared buffers for copying the relation
> > e.g. index_copy_data(), heapam_relation_copy_data().
>
> That's not at all comparable. We hold an exclusive lock on the relation at
> that point, and we don't have a separate implementation of reading tuples from
> the table or something like that.

I don't think there's a way to do this that is perfectly clean, so the
discussion here is really about finding the least unpleasant
alternative. I *really* like the idea of using pg_class to figure out
what relations to copy. As far as I'm concerned, pg_class is the
canonical list of what's in the database, and to the extent that the
filesystem happens to agree, that's good luck. From that perspective,
using the filesystem to figure out what to copy is by definition a
hack.