On 3/30/16 4:18 AM, Magnus Hagander wrote: > > On Wed, Mar 30, 2016 at 4:10 AM, David Steele <da...@pgmasters.net > <mailto:da...@pgmasters.net>> wrote: > > This certainly looks like it would work but it raises the barrier for > implementing backups by quite a lot. It's fine for backrest or barman > but it won't be pleasant for anyone who has home-grown scripts. > > > How much does it really raise the bar, though? > > It would go from "copy all files and make damn sure you copy pg_control > last, and rename it to pg_control.backup" to "take this binary blob you > got from the server and write it to pg_control.backup"? > > Also, the target of these APIs is specifically the backup tools and not > homewritten scripts.
Then what would home-grown scripts use, the deprecated API that we know has issues? > A simple shellscript will have trouble enough using > it in the first place since it requires a persistent connection to the > database. All that's required is to spawn a psql process. I'm no shell expert but that's simple enough. > But those scripts are likely broken anyway. Yes, probably. Backup and especially archiving correctly are harder than most people realize. > <...> > > The main reason for Heikki to suggest this one over the other basic one > is that it brings protection against the "backup script/program crashed > halfway through but the user still tried to restore from that". They will > outright fail because there is no pg_control.backup in that case. But if we are going to make this complicated I'm not sure it's a big deal just to require pg_control to be copied last. pgBackRest already does that and Barman probably does, too. I don't see "don't copy pg_control" and "copy pg_control last" as all that different in terms of complexity. pgBackRest also *restores* pg_control last which I think is pretty important and would not be addressed by this solution. > If we > don't care about that, then we can go back to just saying "copy > pg_control last and we're done". But you yourself complained about that > requirement because it's too easy to get wrong (though you advocated > using backup_label to transfer the data over -- but that has the > potential for getting more complicated if we now or at any point in the > future want more than one field to transfer, for example). Perhaps. I'm still not convinced that getting some information from backup_label and other information from pg_control is a good solution. I would rather write the recovery point into the backup_label and use that instead of the value in pg_control. Text files are much easier to parse and push around accurately (and test). -- -David da...@pgmasters.net -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers