Re: Patch: Implement failover on libpq connect level.

On Mon, Nov 14, 2016 at 8:09 PM, Tsunakawa, Takayuki
<tsunakawa.takay@jp.fujitsu.com> wrote:
> From: pgsql-hackers-owner@postgresql.org
>> [mailto:pgsql-hackers-owner@postgresql.org] On Behalf Of Mithun Cy
>> Thanks, my concern is suppose you have 3 server in cluster A(new version),
>> B(new version), C(old version). If we implement as above only new servers
>> will send ParameterStatus message to indicate what type of server we are
>> connected. Server C will not send same. So we will not be able to use new
>> feature "failover to new master" for such a kind of cluster.
>
> No, the streaming replication requires the same major release for all member servers, so there's no concern about the
mixed-versioncluster.
 

True, but there is a concern about a newer libpq connecting to older
servers.  If we mimic what JDBC is already doing, we'll be compatible
and you'll be able to use this feature with a v10 libpq without
worrying about whether the target server is also v10.  If we invent
something new on the server side, then you'll need to be sure you have
both a v10 libpq and v10 server.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company