Re: Streaming replication failover/failback

On Nov 16, 2016, at 4:24 PM, Adrian Klaver <adrian.klaver@aklaver.com> wrote:

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
-----------------------------------------------

-- 
Adrian Klaver
adrian.klaver@aklaver.com


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