[Proposal]: postgres 18 and major version

[widowild1]

Proposal Summary

update a documentation and docker-compose.yaml for postgres 18

Motivation and Context

Hello,
I have just reported that since Postgres 18 has changed the path of a folder under Docker, this should be added to the documentation and a switchover should be planned in docker-compose.yaml

Changing from postgres =< postgres 17
foo:/var/lib/postgresql/data

To >= postgres 18

foo:/var/lib/postgresql/MAJOR/docker

For example, for version 19, we get:

foo:/var/lib/postgresql/19/docker

tianon/docker-postgres-upgrade#120
docker-library/postgres#1259
https://hub.docker.com/_/postgres/

Proposed Solution

Changing from postgres =< postgres 17
foo:/var/lib/postgresql/data

To >= postgres 18

foo:/var/lib/postgresql/MAJOR/docker

For example, for version 19, we get:

foo:/var/lib/postgresql/19/docker

tianon/docker-postgres-upgrade#120
docker-library/postgres#1259
https://hub.docker.com/_/postgres/

Alternatives Considered

No response

Impact and Risks

Confusion during major Postgres updates

Additional Context or References

No response

Checklist

• I have reviewed existing proposals to ensure this change hasn't been proposed before.
• I agree to provide follow-up updates and maintain discussion on this proposal.
• I agree to follow the project's contribution guidelines.

[widowild1]

Add sources:

docker-library/postgres#1259
docker-library/postgres#37

[Momi-V]

This also changes the VOLUME to /var/lib/postgresql, which should be more reasonable, and make the docker-library/postgres#37 more obvious.
source

Those sources explicitly state to set the volume/bind to foo:/var/lib/postgres NOT foo:/var/lib/postgres/MAJOR/docker The container will store it's data in /var/lib/postgres/MAJOR/docker, but that mustn't be the exact path mounted since it completely breaks upgrades and could lead to the new container storing the data after an upgrade/import outside of the volume (like on 18->19 upgrade shuffling data from /var/lib/postgres/18 (persistent) to /var/lib/postgres/19 (ephemeral) unless the compose is extended by a second volume prior to the upgrade) leading to potential data loss.

Using a single volume mount to /var/lib/postgres sidesteps all those issues, letting the different postgres versions just use their respective subdirectories. This also enables the use of --link during the upgrade since both data locations are now part of the same mount point, significantly improving upgrade speed.