Ok, I got the point.
At Wed, 19 Apr 2017 17:39:01 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp> wrote in
<20170419.173901.16598616.horiguchi.kyotaro@lab.ntt.co.jp>
> > >> | <para>
> > >> | Quorum-based synchronous replication is basically more
> > >> | efficient than priority-based one when you specify multiple
> > >> | standbys in <varname>synchronous_standby_names</> and want
> > >> | to synchronously replicate transactions to two or more of
> > >> | them.
"Some" means "not all".
> > >> | In the priority-based case, the replication master
> > >> | must wait for a reply from the slowest standby in the
> > >> | required number of standbys in priority order, which may
> > >> | slower than the rest.
Quorum-based synchronous replication is expected to be more
efficient than priority-based one when your master doesn't need
to be in sync with all of the nominated standbys by
<varname>synchronous_standby_names</>. While quorum-based
replication master waits only for a specified number of fastest
standbys, priority-based replicatoin master must wait for
standbys at the top of the list, which may be slower than the
rest.
regards,
--
Kyotaro Horiguchi
NTT Open Source Software Center
