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

On Tue, Feb 8, 2022 at 12:09:08PM -0500, Robert Haas wrote:
> Sadly, it doesn't appear to me that anyone has done any performance
> testing of this patch, along the lines suggested above or otherwise,
> and I think it's a crucial question for the patch. My reading of this
> thread is that nobody really likes the idea of maintaining two methods
> for performing CREATE DATABASE, but nobody wants to hose people who
> are using it to clone large databases, either. To some extent those
> things are inexorably in conflict. If we postulate that the 10TB
> template database is on a local RAID array with 40 spindles, while
> pg_wal is on an iSCSI volume that we access via a 128kB ISDN link,
> then the new system is going to be infinitely worse. But real
> situations aren't likely to be that bad, and it would be useful in my
> opinion to have an idea how bad they actually are.

Honestly, I never understood why the checkpoint during CREATE DATABASE
was as problem --- we checkpoint by default every five minutes anyway,
so why is an additional two a problem --- it just means the next
checkpoint will do less work. It is hard to see how avoiding
checkpoints to add WAL writes, fscyncs, and replication traffic could be
a win.

I see the patch justification outlined here:

https://www.postgresql.org/message-id/CAFiTN-sP6yLVTfjR42mEfvFwJ-SZ2iEtG1t0j=QX09X=BM+KWQ@mail.gmail.com

TDE is mentioned as a value for this patch, but I don't see why it is
needed --- TDE can easily decrypt/encrypt the pages while they are
copied.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

If only the physical world exists, free will is an illusion.