[tarantool-patches] Re: [PATCH] replication: display correct status at upstream

[Konstantin Osipov <kostja@tarantool.org>]

* Konstantin Osipov <kostja@tarantool.org> [18/04/28 23:30]:

> * Konstantin Belyavskiy <k.belyavskiy@tarantool.org> [18/04/27 13:43]:
> > This fix improves 'box.info.replication' output.
> > If downstream fails and thus disconnects from upstream, improve
> > logging by printing 'status: disconnected'.
> > Add relay_state { NONE, CONNECTED, DISCONNECTED } to track replica
> > presence, once connected it either CONNECTED or DISCONNECTED until
> > master is reset.
> > 
> > Closes #3365
> 
> Hi,
> 
> the patch is very good, almost ready to push, but I would like to
> request  more work.
> 
> First, a very minor reason why I'm not pushing it right away is
> that I believe relay states should be matched with applier states.
> 
> The matching applier states are OFF, FOLLOW and STOPPED. 
> I think it would be easier for users if we don't invent new states
> on relay side. 
> 
> Second, we allocate relay object on stack; this seems to be a historical
> artifact, we have had struct relay before we got struct replica.
> Relay has a diagnostics area, so by keeping the relay around we
> will be able to display the last error in a way similar to
> applier. 
> 
> I'm not talking about pushing the message back from the applier to
> relay - this seems to be an unnecessary hassle and will complicate
> things quite a bit.

One more thing. As I wrote earlier, it is difficult or impossible
to reliable deliver the error message from applier to the relay.
But what we could do at the relay side, if we see that state is
"stopped" and there is no message in relay->diag, we could set a
helper error ER_RELAY_STOPPED "Please check peer upstream status
fin box.info.replication for reason". This would direct users
towards finding the cause of the problem.

-- 
Konstantin Osipov, Moscow, Russia, +7 903 626 22 32
http://tarantool.io - www.twitter.com/kostja_osipov