Improve error message on switchover

[Jan-M]

On a high load cluster, the shutdown of the master may take longer than patronictl waits.

This yields the following error:

Switchover failed, details: 503, Switchover status unknown

In fact at this state the master is still in shutdown mode and the switch over is still happening once shut down. Not yet sure what to write, but "failed" sounds like nothing is going to happen and master is fine.

[Wolfsrudel]

Which timeout is decisive for this and how can I adjust it?

[vinhnd20]

Can someone explain for me the mechanism of selecting candidate to promote master, pls?

[CyberDem0n]

@vinhnd20 I would recommend you to watch https://www.youtube.com/watch?v=SrFsInsK1ts.
Unfortunately translation isn't perfect, but it's better than nothing.
Slides are available here (slightly newer version): https://github.com/patroni-training/2019