On 2015-01-22 14:42:18 -0600, Jim Nasby wrote: > On 1/22/15 1:43 PM, Alvaro Herrera wrote: > >Andres Freund wrote: > > > >>2) Make movedb() (and possibly created(), not sure yet) use proper WAL > >> logging and log the whole copied data. I think this is the right long > >> term fix and would end up being much more reliable. But it either > >> requires some uglyness during redo (creating nonexistant database > >> directories on the fly during redo) or new wal records. > >> > >> Doable, but probably too large/invasive to backpatch. > > > >Not to mention the extra WAL traffic ... > > Yeah, I don't know that we actually want #2. It's bad enough to copy > an entire database locally
The local copy is pretty much fundamental. Given that tablespaces usually will be on different filesystems there's not much else we can do. If we want a optimization for moving databases across tablespaces if both are on the same filesystems and wal_level < archive, we can do that. But that's pretty independent. And I doubt it's worthwile the developer time. > , but to then put it's entire contents into WAL? Blech. Besides actually having a chance of being correct, doing so will save having to do two checkpoints inside movedb(). I think it's pretty likely that that actually saves overall IO, even including the WAL writes. Especially if there's other databases in the cluster at the same time. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
