Re: Implement UNLOGGED clause for COPY FROM

On Thu, Aug 27, 2020 at 7:04 AM tsunakawa(dot)takay(at)fujitsu(dot)com
<tsunakawa(dot)takay(at)fujitsu(dot)com> wrote:
>
> From: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> > So you want your users to shutdown and restart the server before Copy
> > because that would be required if you want to change the wal_level.
>
> Yes. They seem to be fine with it, as far as I heard from a person who is involved in the system design.
>
>
> > However, even if we do that, users who are running the server
> > previously with wal_level as 'replica' won't be happy after doing this
> > change. Because if they change the wal_level to 'none' for certain
> > operations like bulk load and then again change back the mode to
> > 'replica' they need to back up the database again to setup 'replica'
> > as they can't continue replication from the previous point (consider
> > update on a page for which previously WAL was not written).
>
> Yes, it requires the database backup. The database backup should be a daily task anyway, so I expect it wouldn't impose extra maintenance burdon on the user.
>

Sure, but on a daily basis, one requires only incremental WAL to
complete the backup but in this case, it would require the entire
database back up unless we have some form of block-level incremental
backup method. OTOH, I don't deny that there is some use case with
wal_level = 'none' for initial data loading as MySQL provides but I
think that is a separate feature than what is proposed here (Copy
Unlogged). It might be better if you can start a separate thread for
that with some more details on the implementation side as well.

--
With Regards,
Amit Kapila.