Postgres 18 Changelog (#56)

* Mount postgres volumes at /var/lib/postgresql

This is to resolve errors like the following, now that postgres:latest
resolves to the v18 image by default.

```quote
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 docker-library/postgres#1259

Counter to that, there appears to be PostgreSQL data in:
  /var/lib/postgresql/data (unused mount/volume)

This is usually the result of upgrading the Docker image without
upgrading the underlying database using "pg_upgrade" (which requires both
versions).

The suggested container configuration for 18+ is to place a single mount
at /var/lib/postgresql which will then place PostgreSQL data in a
subdirectory, allowing usage of "pg_upgrade --link" without mount point
boundary issues.

See docker-library/postgres#37 for a (long)
discussion around this process, and suggestions for how to do so.
```

* Limit version to Postgres 18. Add Changelog entry.

---------

Co-authored-by: Matt Gallagher <mjg1992@hotmail.co.uk>

Author: stevensJourney

CHANGELOG.md

@@ -1,5 +1,29 @@
 # PowerSync Self Hosted Example
 
+## 2025-11-25
+
+### Postgres 18 Upgrade
+
+Updated Postgres demos for Postgres 18 compatibility. Postgres 18 contains breaking changes for Docker volume mount points. First time demo runners should be able to start the demo using the standard `docker compose up` commands.
+
+Users with existing configurations should either:
+
+#### Start from a clean slate
+
+With the relevant demo directory as the current working directory, run:
+
+```bash
+# Clear previous data (this deletes Docker volumes)
+docker compose down --volumes
+
+# Run the demo
+docker compose up
+```
+
+#### Migrate existing data
+
+See https://github.com/docker-library/postgres/issues/37 for options.
+
 ## 2025-05-13
 
 - Updated YAML config files to use published schema

demos/nodejs-postgres-bucket-storage/docker-compose.yaml

@@ -27,7 +27,7 @@ services:
       - ../nodejs/init-scripts:/docker-entrypoint-initdb.d
 
   pg-storage:
-    image: postgres:latest
+    image: postgres:18
     restart: always
     environment:
       - POSTGRES_USER=${PG_STORAGE_DATABASE_USER}
@@ -39,7 +39,11 @@ services:
     ports:
       - "${PG_STORAGE_DATABASE_PORT}:${PG_STORAGE_DATABASE_PORT}"
     healthcheck:
-      test: ["CMD-SHELL", "pg_isready -U ${PG_STORAGE_DATABASE_USER} -d ${PG_STORAGE_DATABASE_NAME}"]
+      test:
+        [
+          "CMD-SHELL",
+          "pg_isready -U ${PG_STORAGE_DATABASE_USER} -d ${PG_STORAGE_DATABASE_NAME}",
+        ]
       interval: 5s
       timeout: 5s
       retries: 5

services/postgres.yaml

@@ -1,6 +1,6 @@
 services:
   pg-db:
-    image: postgres:latest
+    image: postgres:18
     restart: always
     environment:
       - POSTGRES_USER=${PG_DATABASE_USER}