Re: pglogical most basic setup for logical replication

On 26 January 2016 at 19:18, Sebastien Diemer <
sebastien(dot)diemer(at)polyconseil(dot)fr> wrote:

> It sounds like you must be running on PostgreSQL 9.4.
>
> Indeed I am on PostgreSQL 9.4, I omitted this important point.
>
>
I'll update the docs to mention the extra step on 9.4.

> You'll need to drop the subscriber database and re-create it. Use a new
>> node name.
>
> Seems to work but I still do not really understand what was wrong in the
> first place though.
> Thanks for your help Craig !
>

It's because internally pglogical relies on pg_dump and pg_restore to set
up the initial database state. If it fails partway through a pg_restore
there's no sensible way to undo those changes, especially since we have to
do it in a number of steps to achieve a partial restore.

A cleaner handling of this really requires the ability to use pg_dump's
functionality over a normal protocol connection from SQL, or at least as a
library.

The error should probably get a HINT to say that an incomplete restore
means the DB may have to be dropped and recreated.

It's all a bit messy, since we support multiple upstreams and support
writes directly into the downstream. So you actually can't always just drop
the downstream. A really good solution to this needs the ability to compare
various objects (type definitions, tables, etc), the ability to extract
just a required subset of dependencies from a database and other
complexities.

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