From: | Craig Ringer <craig(at)2ndquadrant(dot)com> |
---|---|
To: | Sebastien Diemer <sebastien(dot)diemer(at)polyconseil(dot)fr> |
Cc: | PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: pglogical most basic setup for logical replication |
Date: | 2016-01-26 14:41:44 |
Message-ID: | CAMsr+YE9oT8EGSzWgny+H1aHT0D3dwqXfAoXU7Y3wbK+-5rV-Q@mail.gmail.com |
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Lists: | pgsql-hackers |
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
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