[pgpool-general: 5634] Question about pgpool upgrade procedure

[Thomas Delacotte]

Hi everyone,

I need to upgrade a two-nodes PostgreSQL cluster with streaming 
replication. The cluster is running PostgreSQL 9.5.4 and PGpool 3.5.4 is 
deployed on each node. The OS used is Ubuntu 16.04.

After the upgrade I will end up with the following versions (using 
postgres apt repositories):

- PostgreSQL 9.5.7

- Pgpool 3.6.4

Although I'm quite confident with the PostgreSQL version switching, I'm 
more concerned about switching Pgpool from 3.5.4 to 3.6.4. I couldn't 
find any specific documentation related to upgrade procedures so I came 
up with following one, trying to minimize downtime:

- First, upgrade the standby node

- Check that replication is up and running and that the upgraded pgpool 
can communicate with the other pgpool instance

- Failover on the upgraded standby node so it becomes the new master

- Upgrade the old master and make it join the cluster as standby node

- Get back to "normal" state with the first node becoming the master 
again (although it's not really mandatory)


Now here comes my questions

- In your opinion, does this procedure seem accurate ?

- Can different versions of pgpool actually communicate with each other 
without any issues (obsolete configuration params, changes in 
communication protocols, etc...) ? Release notes from 3.5.4 to 3.6.4 
don't show any BC breaks but I'd like a confirmation.

Regards,

Thomas