I've recently open sourced this template for managing state for PostgreSQL: https://github.com/compose/governor
Take a test drive around it. As long as the old Leader is verifiably dead or stopped at the forked WAL log point, I've not had issues with inserting a `recovery.conf` to tail the new Leader. On Tue, Apr 7, 2015 at 5:16 PM, Jim Nasby <jim.na...@bluetreble.com> wrote: > On 3/11/15 5:27 AM, Deole, Pushkar (Pushkar) wrote: > >> Hi, >> >> I am new to postgresql and evaluating the streaming replication for my >> use case. My use case is: >> >> 1.Need to replicate data from primary database (master) to secondary >> database (slave) asynchronously. >> >> 2.If master goes down, the slave should automatically be promoted to >> master. >> >> 3.Later, when the original primary server (original master) is brought >> up again, it should obtain back its master role and the new master >> should assume the slave again as it was with original setup. >> >> For #1, the streaming replication of postgresql is good enough. >> >> For #2, we need to create the trigger file. How can we do this >> automatically? >> > > You'll need to use something else to figure out that the master node died. > But that's not the big problem... the big problem is you need to be careful > to ensure you don't get into a 'split brain' state. > > Say you promoted the slave, so now it's responding to all queries. Now the > master suddenly starts. Not only is the master missing data that's been > written to the slave, but if you have a load balancer now *both* databases > are acting as if they're the master. > > That's bad. :) > > Typically, you want some way to "Shoot The Other Node In The Head" before > you promote the slave. For example, you could modify the configuration of > something in your network so it's no longer possible to reach the old > master. > > For #3, this seems to be quite complicated. Is this even possible using >> streaming replication? If yes, how can this be achieved? >> > > You basically need to replace the master with a new replica built off the > new master. There's been some recent work to make this easier/faster to do, > but it's not terribly trivial, and you have to be careful to do it > correctly. > -- > Jim Nasby, Data Architect, Blue Treble Consulting > Data in Trouble? Get it in Treble! http://BlueTreble.com > > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general >
