Re: Streaming replication failover/failback

On 11/16/2016 04:51 PM, Israel Brewster wrote:
> I've been playing around with streaming replication, and discovered that
> the following series of steps *appears* to work without complaint:
>
> - Start with master on server A, slave on server B, replicating via
> streaming replication with replication slots.
> - Shut down master on A
> - Promote slave on B to master
> - Create recovery.conf on A pointing to B
> - Start (as slave) on A, streaming from B
>
> After those steps, A comes up as a streaming replica of B, and works as
> expected. In my testing I can go back and forth between the two servers
> all day using the above steps.
>
> My understanding from my initial research, however, is that this
> shouldn't be possible - I should need to perform a new basebackup from B
> to A after promoting B to master before I can restart A as a slave. Is
> the observed behavior then just a "lucky fluke" that I shouldn't rely

You don't say how active the database is, but I going to say it is not
active enough for the WAL files on B to go out for scope for A in the
time it takes you to do the switch over.

> on? Or is it expected behavior and my understanding about the need for a
> new basebackup is simply off? Does the new pg_rewind feature of 9.5
> change things? If so, how?
>
> Thanks for your time!
> -----------------------------------------------
> Israel Brewster
> Systems Analyst II
> Ravn Alaska
> 5245 Airport Industrial Rd
> Fairbanks, AK 99709
> (907) 450-7293
> -----------------------------------------------
>
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--
Adrian Klaver
adrian.klaver@aklaver.com