Sorry if this is a dumb question. Feel free to just point me to a doc.
I've read a little about Postgres replication and the concept of a
master and one or more slaves. If one db is down then you just switch
to one that's still running. There's even additional software like
pgpool to make the switch easy. But I want to know more about how to
resume normal operating mode.
For example, I take it that if the master is unavailable then you
switch to a slave. The former slave becomes the current master. When
the original "master" is ready to run and network accessible then do
you bring it online in slave mode and it syncs automatically with the
current master? At which time you're almost back to normal. Once they
are back in sync do people typically switch the roles back to the
original designation of who's a slave and who's a master? It's not
clear to me if the last step is necessary.
Well, that's assuming that the master comes back online with all the
data it had when it went offline. If it comes back but all data was
lost (a worst case scenario) then I assume I have to take the current
master offline and use it to repopulate the recovering master from
scratch, correct? But... if I have additional slaves then I could just
take one of the current slaves offline, use it to rebuild the original
master, and then bring both the slave and the reconstructed master
(now also a slave) back online and both will sync with the current
master.
John