Re: Resync second slave to new master

On Tue, Mar 06, 2018 at 04:45:10AM +0000, Dylan Luong wrote:
> After a failover (promote) to the Slave1,  is it easily resync the
> Slave2 to the new master (old slave1)? Do we need to do  full rebuild
> of the Slave2 from new master everytime we failover to Slave1 from
> Master? Can we use pg_rewind on Slave2 to resyn it with new master
> (old slave1)?

After promoting slave 1, it could be possible that some records have
slipped to slave 2 from the primary.  In this case, a rewind would be
recommended.  You should be careful that your slave 2 has not received
WAL to a position newer than where WAL has forked because of the
promotion.  If that happened, then a rewind would be necessary before
replugging slave 2 to the newly-promoted server.  Be very careful with
your failover flow here.  pg_rewind also would not run if it finds that
the target server does not need a rewind, so you could stop the slave 2,
and run pg_rewind unconditionally to keep things simple.
--
Michael