On 21 November 2016 at 00:08, Mithun Cy <mithun...@enterprisedb.com> wrote:

>> Please avoid adding another round trip by using a GUC_REPORTed variable
>> (ParameterStatus entry).  If you want to support this libpq failover with
>> >pre-10 servers, you can switch the method of determining the primary based
>> on the server version.  But I don't think it's worth supporting older
>> servers > at the price of libpq code complexity.
> Currently there is no consensus around this. For now, making this patch to
> address failover to next primary as similar to JDBC seems sufficient for me.
> On next proposal of patch I think we can try to extend as you have proposed

FWIW, I agree. Working first, then improved.

>> I haven't tracked the progress of logical replication, but will
>> target_server_type be likely to be usable with it?  How will
>> target_server_type fit logical       > replication?
> I tried to check logical replication WIP patch, not very sure how to
> accomodate same.

Logical replication downstreams won't force transactions to read-only.
A significant part of the appeal of logical replication is that you
can use temp tables and unlogged tables on the downstream, and even
use persistent tables so long as they don't clash with the upstream.
More sophisticated models even allow the downstream to safely write to
replicated tables by doing conflict resolution.

So as it stands, this patch would consider any logical replication
downstream a 'master'.

That's fine for now IMO. Determining whether a server is a logical
replica isn't that simple, nor is it a clear-cut yes/no answer, and I
think it's out of the scope of this patch to deal with it. Figure it
out once logical replication lands.

 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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