Ruby on Rails solid cache, cable, queue with mulitple database on Heroku

Running Rails 8 Solid Cache, Queue & Cable on Heroku with Multiple Databases

Rails 8 ships with the Solid trifecta:

Solid Cache durable, DB-backed cache store
Solid Queue jobs without Redis
Solid Cable Action Cable on Postgres

Together, they let you drop Redis entirely and run your whole stack on Postgres. Perfect for Heroku… but there are a few gotchas if you want to isolate each component into its own database.

This article shows how I set up Rails 8 + Heroku with:

Primary DB → app data + jobs (Solid Queue) + websockets (Solid Cable)
Cache DB → Solid Cache (kept separate to avoid bloat) (but you can run on 3 different DB)

Why multiple databases?

Solid’s docs suggest splitting out Cache/Queue/Cable into separate DBs. On Heroku you can start simple (1 DB for everything), but caches tend to churn. If you expect lots of API hits or domain-level caching, isolating Solid Cache is cheap insurance:

Primary stays lean → your schema/migrations aren’t slowed by millions of cache rows.
Cache is disposable → you can drop & recreate it without touching app data.
Scaling knobs → you can upgrade just the cache DB if needed.

Database.yml setup

Rails already wires up multi-DB. In production, switch to url: so Heroku env vars work:

production:
  primary:
    <<: *default
    url: <%= ENV["DATABASE_URL"] %>

  cache:
    <<: *default
    url: <%= ENV["CACHE_DATABASE_URL"] || ENV["DATABASE_URL"] %>
    migrations_paths: db/cache_migrate

  queue:
    <<: *default
    url: <%= ENV["DATABASE_URL"] %>
    migrations_paths: db/queue_migrate

  cable:
    <<: *default
    url: <%= ENV["DATABASE_URL"] %>
    migrations_paths: db/cable_migrate

Cache.yml

Rails tells Solid Cache which DB to use via config/cache.yml:

production:
  database: cache
  store_options:
    namespace: production

Don’t duplicate the config in production.rb. Just:

# config/environments/production.rb
config.cache_store = :solid_cache_store

That’s it. Solid will pick up the cache connection from cache.yml.

Installing the schemas

Solid creates db/cache_schema.rb, db/queue_schema.rb, db/cable_schema.rb.

Put each into its own migration folder:

db/cache_migrate/init_solid_cache.rb
db/queue_migrate/init_solid_queue.rb
db/cable_migrate/init_solid_cable.rb

Each migration just loads the schema:

class InitSolidCache < ActiveRecord::Migration[8.0]
  def up
    load Rails.root.join("db/cache_schema.rb")
  end
  def down = raise ActiveRecord::IrreversibleMigration
end

Rails knows which DB to run it against based on the folder.

Run once:

bin/rails db:migrate

All four DBs (primary + cache + queue + cable) will be created and seeded.

Heroku setup

Provision two Postgres add-ons:

heroku addons:create heroku-postgresql:essential-0   # primary
heroku addons:create heroku-postgresql:essential-0        # cache

Alias the second one:

heroku config:set CACHE_DATABASE_URL=$(heroku config:get HEROKU_POSTGRESQL_BLUE_URL)

Deploy + migrate:

git push heroku main
heroku run rails db:migrate

Smoke tests

Cache write/read in your heroku console

Rails.cache.write("smoke:key","ok",expires_in:60)
puts Rails.cache.read("smoke:key")

Queue enqueue:
ApplicationJob.perform_later("smoke") # should see the job run (if SOLID_QUEUE_IN_PUMA=1)

Cleanup job (recommended)

Caches grow. Add a nightly cleanup to delete expired entries

Lessons learned

Don’t duplicate config: pick cache.yml or production.rb for Solid Cache, not both.
Each schema file lives in its own db/*_migrate folder → Rails handles connections.
Add test.cache/queue/cable entries in database.yml to avoid KeyErrors in dev.
Start with 1 DB if you’re unsure. Splitting out cache is a 5-minute change later.

Pricing
each DB costs 10$/month on Heroku so make sure you need it ;)

#solid cable 🇬🇧

Ruby on Rails solid cache, cable, queue with mulitple database on Heroku

Running Rails 8 Solid Cache, Queue & Cable on Heroku with Multiple Databases

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