On Sat, Mar 4, 2017 at 11:41 AM, Petr Jelinek <petr.jeli...@2ndquadrant.com> wrote: > On 04/03/17 06:46, Robert Haas wrote: >> On Tue, Feb 28, 2017 at 12:08 PM, Erik Rijkers <e...@xs4all.nl> wrote: >>> Would you remind me why synchronous_commit = on was deemed a better default? >> I'm wondering about that, too. If you're trying to do logical >> synchronous replication, then maybe there's some argument there, >> although even in that case I am not sure it's actually necessary. But >> if you're doing asynchronous logical replication, it seems not to make >> much sense. I mean, walwriter is going to flush the WAL to disk >> within a fraction of a second; why would we wait for that to happen >> instead of getting on with replicating the next transaction meanwhile? >> > > I do agree. And even when doing synchronous replication it should not be > problem. We do have code already in place which takes care of reporting > correct write/flush position in the situation where upstream does > syncrep but downstream has synccommit off. > > The only anomaly I could think of in terms of having sync commit off on > downstream is that some replicated data that were visible will disappear > after a crash only to reappear again once replication catches up to > where it has been before when doing asynchronous replication. That does > not strike me like good enough reason to have by default something like > order of magnitude worse performance.
I see. That's a good reason to have an option, but I agree with your conclusion. > So I think we should do it, but it needs to be configurable, my original > patch added GUC for it, Peter wanted it to be configurable per > subscription. I guess we could add it as another option to the list of > WITH (...) options for CREATE and ALTER SUBSCRIPTION. I don't have a terribly well-considered opinion on this point just yet, but my initial hunch is that Peter has the right idea. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers