Re: Remove Deprecated Exclusive Backup Mode

On 2/22/19 7:10 PM, Robert Haas wrote:
> On Fri, Feb 22, 2019 at 12:35 PM Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>> -1 for the removal. I think that there are still many users of an exclusive
>> backup API, and it's not so easy to migrate their backup scripts so that
>> only non-exclusive one is used because of the reason I wrote in another thread.
>> https://postgr.es/m/CAHGQGwHUkEbkVexVfWNLjmq2rzOS_SHYMiECt+KBn-cBPq5Arg@mail.gmail.com
>
> Yeah, those are interesting points. Unfortunately, I think something
> as simple as your proposed...
>
> psql -c "SELECT pg_start_backup()"
> rsync, cp, tar, storage backup, or something
> psql -c "SELECT pg_stop_backup()"
>
> ...doesn't have much chance of being correct. If you aren't checking
> whether pg_start_backup() throws an error, for example, you have got a
> very failure-prone set-up. That being said, it's possible to fix that
> problem using some shell logic, whereas the problem of keeping a
> connection open for the duration of the backup from the shell is much
> harder. I recently ran across a case where someone attempted it but
> did not get the logic entirely right, with rather painful
> consequences.
>
> Now you might say that people should not write their own tools and
> just use professionally produced ones. But I don't really agree with
> that, and whatever we think people SHOULD do, there are in fact a lot
> of people using their own tools.
>

FWIW +1 for not remove exclusive backup.

Maintain a connection during the backup is a hard pre-requisite. In my
previous jobs I already done custom scripts to perform backup by using
pre/post backup hook to control backup software: With vmware to do PITR
backup with VM snapshot or with another file backup tool which perform
block deduplication. I do not see where is the problem if you check
pg_start_backup()/pg_stop_backup() went well?

It will be annoying if after this removal, companies must change their
backup strategy by using specific postgres tools (pgbackrest, barman).

Regards,