Re: Remove Deprecated Exclusive Backup Mode

On Wed, Jul 1, 2020 at 3:50 PM Magnus Hagander <magnus@hagander.net> wrote:
> As far as I've seen, the one thing that people have problems with in the exclusive mode backups are precisely the
factthat they have to keep a persistent conneciton open, and thus it cannot work together with backup software that is
limitedto only supporting running a pre- and a post script. 
>
> Something like I have suggested here is to solve *that* problem. I don't think anybody actually explicitly wants
"exclusivebackups" -- they want a backup solution that plugs into their world of pre/post scripts. And if we can make
thatone work in a safer way than the current exclusive backups, ohw is that not an improvement? 

Yeah, I guess that's a pretty fair point. I have to confess to having
somewhat limited enthusiasm for adding a third mode here, but it might
be worth it.

It seems pretty well inevitable to me that people are going to forget
to end them. I am not sure exactly what the consequences of that will
be, but if for example there's a limited number of shared memory slots
to store information about these backups, then if you leak any, you'll
eventually run out of slots and your backups will start failing. I
feel like that's a going to happen to about 75% of the people who try
to use this new backup mode at some point in time, but maybe I'm a
pessimist.[1]

If we could jigger things so that you don't need to stop the backup at
all, you only start it, and whether you ever finish copying everything
is something about which the system need not know or care, that would
be a lot nicer. I'm not sure I see how to do that, though.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

[1] OK, that's not really a "maybe".