On Mon, Feb 1, 2016 at 11:28 PM, Fujii Masao <masao.fu...@gmail.com>wrote:
> [first version] > Add only synchronous_standby_num which specifies the number of standbys > that the master must wait for before marking sync replication as completed. > This version supports simple use cases like "I want to have two synchronous > standbys". > > [second version] > Add synchronous_replication_method: 'prioriry' and 'quorum'. This version > additionally supports simple quorum commit case like "I want to ensure > that WAL is replicated synchronously to at least two standbys from five > ones listed in s_s_names". > > Or > > Add something like quorum_replication_num and quorum_standby_names, i.e., > the master must wait for at least q_r_num standbys from ones listed in > q_s_names before marking sync replication as completed. Also the master > must wait for sync replication according to s_s_num and s_s_num. > That is, this approach separates 'priority' and 'quorum' to each > parameters. > This increases the number of GUC parameters, but ISTM less confusing, and > it supports a bit complicated case like "there is one local standby and > three > remote standbys, then I want to ensure that WAL is replicated synchronously > to the local standby and at least two remote one", e.g., > > s_s_num = 1, s_s_names = 'local' > q_s_num = 2, q_s_names = 'remote1, remote2, remote3' > > [third version] > Add the hooks for more complicated sync replication cases. > > I'm thinking that the realistic target for 9.6 might be the first one. > If we want to get something out for this release, clearly yes, and being able to specify 2 sync targets is already a win when the two sync standbys are not exactly at the same location. FWIW, I don't doing coding and/or review work, that's basically my first patch that needs a bit more love and polishing, *and* test cases but I am used enough to perl and PostgresNode these days to produce something based on sanity checks of pg_stat_replication and my other set of patches that have more basic routines. Now I would not mind if we actually jump into the 3rd case if we are fine with doing nothing for this release, but this requires a lot of design and background work, so that's not plausible for 9.6. Of course if there are voices against the scenario proposed by Fujii-san others feel free to speak up. -- Michael
