On Thu, 17 Nov 2016 08:26:59 -0900
Israel Brewster <israel@ravnalaska.net> wrote:
> > 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.
>
> Yeah, not very - this was just in testing, so essentially no activity. So
> between your response and the one from Jehan-Guillaume de Rorthais, what I'm
> hearing is that my information about the basebackup being needed was
> obsoleted with the patch he linked to, and as long as I do a clean shutdown
> of the master, and don't do too much activity on the *new* master before
> bringing the old master up as a slave (such that WAL files are lost)
Just set up wal archiving to avoid this (and have PITR backup as a side effect).
