On Tue, Oct 6, 2015 at 12:27 PM, Thomas Munro <thomas.mu...@enterprisedb.com > wrote:
> On Sun, Oct 4, 2015 at 11:47 PM, Michael Paquier > <michael.paqu...@gmail.com> wrote: > > (Seems like you forgot to push the Reply-all button) > > > > On Sun, Oct 4, 2015 at 7:01 PM, Madovsky wrote: > >> On 10/3/2015 3:30 PM, Michael Paquier wrote: > >>> and no reason is given to justify *why* this would be needed in your > case > >> reason for a choice can be often an issue for other :D > >> > >> I thought that postgresql 9.4 user could change on the fly with > >> synchronous_commit from local to on for ex > >> which hotstandby would become in sync and which in async to avoid a big > >> latency in case of let's say 100 hot standby. > >> it was an idea, a concept to let the master write and update the nodes, > like > >> a queen bee ;) > >> but I'm afraid it's not possible, so maybe future version of pg will do > it, > >> for now read from the master is my only solution. > > > > Well, Thomas Munro (adding him in CC) has sent for integration with > > 9.6 a patch that would cover your need, by adding to > > synchronous_commit a mode called 'apply', in which case a master would > > wait for the transaction to be applied on standby before committing > > locally: > > > http://www.postgresql.org/message-id/CAEepm=1fqkivl4v-otphwsgw4af9hcogimrcw-ybtjipx9g...@mail.gmail.com > > Perhaps you could help with the review of the patch, this has stalled > > a bit lately. > > That patch (or something more sophisticated long those lines) is a > small piece of a bigger puzzle, though it might be enough if you only > have one standby, are prepared to block until manual intervention if > that standby fails, and don't mind potentially lumpy apply > performance. See also the work being done to separate wal writing > from wal applying for smoother performance[1], and handle multiple > synchronous standbys[2]. But there is another piece of the puzzle > IMHO: how to know reliably that the standby that you are talking to > guarantees causal consistency, while also allowing standbys to > fail/drop out gracefully, and I'm currently working on an idea for > that. > FYI I posted the resulting proposal and patch over on the -hackers list. Feedback, ideas, flames welcome as always. http://www.postgresql.org/message-id/flat/CAEepm=0n_OxB2_pNntXND6aD85v5PvADeUY8eZjv9CBLk=z...@mail.gmail.com -- Thomas Munro http://www.enterprisedb.com
