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

On Thu, Jun 17, 2021 at 5:20 AM Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
> You only need relpersistence if you want to use the buffer cache, right?
> I think that's a good argument for not using it.

I think the root of the problem with this feature is that it doesn't
go through shared_buffers, so in my opinion, it would be better if we
can make it all go through shared_buffers. It seems like you're
advocating a middle ground where half of the operation goes through
shared_buffers and the other half doesn't, but that sounds like
getting rid of half of the hack when we could have gotten rid of all
of it. I think things that don't go through shared_buffers are bad,
and we should be making an effort to get rid of them where we can
reasonably do so. I believe I've both introduced and fixed my share of
bugs that were caused by such cases, and I think the behavior of the
whole system would be a lot easier to reason about if we had fewer of
those, or none.

I can also think of at least one significant advantage of driving this
off the remote database's pg_class rather than the filesystem
contents. It's a known defect of PostgreSQL that if you create a table
and then crash, you leave behind a dead file that never gets removed.
If you now copy the database that contains that orphaned file, you
would ideally prefer not to copy that file, but if you do a copy based
on the filesystem contents, then you will. If you drive the copy off
of pg_class, you won't.

--
Robert Haas
EDB: http://www.enterprisedb.com