[examples / demo] Examples/demo Docker configuration

[andyatkinson]

I have found when running Postgres 18+ in Docker the PGDATA directory has changed to include a major version in it. For example when I cd examples/demo and run docker compose up now, Postgres 18 has its volume and PGDATA configured with /var/lib/postgresql/data which produces the following error when starting up:

Error: in 18+, these Docker images are configured to store database data in a
       format which is compatible with "pg_ctlcluster" (specifically, using
       major-version-specific directory names).  This better reflects how
       PostgreSQL itself works, and how upgrades are to be performed.

       See also https://github.com/docker-library/postgres/pull/1259

When I change it to /var/lib/postgresql then docker compose up works as expected.

--- a/examples/demo/docker-compose.yml
+++ b/examples/demo/docker-compose.yml
@@ -6,7 +6,7 @@ services:
     ports:
       - 6000:5432
     volumes:
-      - shard_0:/var/lib/postgresql/data
+      - shard_0:/var/lib/postgresql

Is the example at examples/demo supported? Do you want a small PR with the above change in each spot?

Thanks.

[levkk]

Please. The demo is pretty old / not maintained and could use some love.