Re: Switching timeline over streaming replication

On 19.12.2012 04:57, Josh Berkus wrote:
> Heikki,
>
> I ran into an unexpected issue while testing. I just wanted to fire up
> a chain of 5 replicas to see if I could connect them in a loop.
> However, I ran into a weird issue when starting up "r3": it refused to
> come out of "the database is starting up" mode until I did a write on
> the master. Then it came up fine.
>
> master-->r1-->r2-->r3-->r4
>
> I tried doing the full replication sequence (basebackup, startup, test)
> with it twice and got the exact same results each time.
>
> This is very strange because I did not encounter the same issues with r2
> or r4. Nor have I seen this before in my tests.

Ok.. I'm going to need some more details on how to reproduce this, I'm
not seeing that when I set up four standbys.

> I'm also seeing Thom's spurious error message now. Each of r2, r3 and
> r4 have the following message once in their logs:
>
> LOG: database system was interrupted while in recovery at log time
> 2012-12-19 02:49:34 GMT
> HINT: If this has occurred more than once some data might be corrupted
> and you might need to choose an earlier recovery target.
>
> This message doesn't seem to signify anything.

Yep. You get that message when you start up the system from a base
backup that was taken from a standby server. It's just noise, it would
be nice if we could dial it down somehow.

In general, streaming replication and backups tend to be awfully noisy.
I've been meaning to go through all the messages that get printed during
normal operation and think carefully which ones are really necessary,
which ones could perhaps be merged into more compact messages. But
haven't gotten around to it; that would be a great project for someone
who actually sets up these systems regularly in production.

- Heikki