I have a production database setup with a primary server and a standby server. The database is currently running on PostgreSQL 15.0, and I plan to upgrade both servers to 15.9.
I have the following questions regarding the upgrade and replication process:
Upgrade and Replication Compatibility:
My plan is to perform a failover, promote the standby server (currently 15.0) to primary, and then upgrade the old primary server to version 15.9.
Try to replicate from old->new version, because bug fixes in newer versions might have broken something in new->old replication.
If you really can't tolerate any downtime, then shutdown and upgrade the Secondary server from 15.0 to 15.10. Once you start it back up, replication from the still-15.0 primary will catch back up to the now-patched Secondary.
Fail over to the Secondary (now new-Primary), and then patch old-Primary to 15.10.
After upgrading the old primary server to version 15.9, I want to configure it as a standby server and set up streaming replication with the new primary server, which will still be running version 15.0.
Is it possible to establish streaming replication between these two versions (15.0 as primary and 15.9 as standby)?
Efficient Replication Setup:
The production database is around 1TB in size, and creating replication using pg_basebackup is taking more than 2–3 hours to complete.
Is there an alternative method to set up replication without taking a full backup of the entire cluster but instead using only the WAL files that have changed on both servers?
pg_rewind is probably what you want. I've never used it, though.
