Re: BDR question on dboid conflicts

On 27 October 2017 at 01:15, Zhu, Joshua <jzhu(at)vormetric(dot)com> wrote:
> Database oid is used in both bdr.bdr_nodes, as node_dboid, and
> bdr.bdr_connections, as conn_dboid, also used in construction of replication
> slot names.

Correct. However, it's used in conjunction with the sysid and node timeline ID.

> I noticed that when trying to join a bdr group, if the database oid on the
> new node happens to be the same as that of an node already in the bdr group,
> the join would fail, and the only way to resolve the conflict that I was
> able to come up with has been to retry with dropping/recreating the database
> until the dboid does not conflict with any node already in the group.

That is extremely surprising. In our regression tests the database
oids should be the same quite often, as we do various tests where we
create multiple instances. More importantly, every time you
bdr_init_copy, you get a clone with the same database oid, and that
works fine.

There's no detail here to work from, so I cannot guess what's actually
happening, but I can confidently say it's not a database oid conflict.
Nowhere in BDR should the database oid be considered without the rest
of the (sysid,timeline,dboid) tuple.

--
Craig Ringer http://www.2ndQuadrant.com/
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