Re: adding a bdr node using bcv backup

On 21 January 2016 at 20:46, (Daniel Stolf) <dstolf(at)gmail(dot)com> wrote:

> So here's what I don't get:
>
> 1) if I have to create a new replication slots on node1 and 2 beforehand
> using "pg_create_physical_replication_slot" , don't they need the if of
> node3 on their name?
>

You need to create a logical replication slot with the 'bdr' plugin, since
that's what BDR uses.

> 2) If node3 has the same name and if as node1, won't that introduce a
> conflic? Don't I need to clean that up before node3 can join the
> replication group?
>

It will not have the same sysid. bdr_init_copy resets it normally. If
you're doing it manually you'd have to run pg_resetxlog with the option to
reset the sysid, create the new slots with the new sysid, then make sure
bdr_init_copy doesn't reset the sysid again it afterwards when it brings
the new node up.

Honestly I don't remember the exact steps that had to be performed before
bdr_init_copy got support for automating the pg_basebackup step. That's the
supported way to do it. I'm trying to prepare some conference presentations
and a new pglogical release so I can't presently dig into it further for
you; you may need to take a look at the bdr_init_copy sources and/or study
how the node bringup works in more detail.

I can see it being useful to add a new mode to bdr_init_copy where you tell
it to generate a sysid and make new slots for that sysid; *then* you make a
snapshot and restore it, then you run bdr_init_copy again to finish
bringup, resetting the sysid to the new value and finishing setup. There's
nothing like that now though.

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