Solid Cable

Solid Cable is a database-backed Action Cable adapter that keeps messages in a table and continously polls for updates. This makes it possible to drop the common dependency on Redis, if it isn't needed for any other purpose. Despite polling, the performance of Solid Cable is comparable to Redis in most situations. And in all circumstances, it makes it easier to deploy Rails when Redis is no longer a required dependency for Action Cable functionality.

Installation

Solid Cable is configured by default in new Rails 8 applications. But if you're running an earlier version, you can add it manually following these steps:

1. bundle add solid_cable
2. bin/rails solid_cable:install

This will configure Solid Cable as the production cable adapter by overwritting config/cable.yml and create db/cable_schema.rb.

You will then have to add the configuration for the cable database in config/database.yml. If you're using SQLite, it'll look like this:

production:
  primary:
    <<: *default
    database: storage/production.sqlite3
  cable:
    <<: *default
    database: storage/production_cable.sqlite3
    migrations_paths: db/cable_migrate

...or if you're using MySQL/PostgreSQL/Trilogy:

production:
  primary: &primary_production
    <<: *default
    database: app_production
    username: app
    password: <%= ENV["APP_DATABASE_PASSWORD"] %>
  cable:
    <<: *primary_production
    database: app_production_cable
    migrations_paths: db/cable_migrate

Note

Calling bin/rails solid_cable:install will automatically setup config/cable.yml, so no additional configuration is needed there (although you must make sure that you use the cable name in database.yml for this to match!). But if you want to use Solid Cable in a different environment (like staging or even development), you'll have to manually add that connects_to block to the respective environment in the config/cable.yml file. And, as always, make sure that the name you're using for the database in config/cable.yml matches the name you define in config/database.yml.

Then run db:prepare in production to ensure the database is created and the schema is loaded.

If you have already installed Solid Cable, run solid_cable:update to get the latest changes to migrations.

Configuration

All configuration is managed via the config/cable.yml file. By default, it'll be configured like this:

production:
  adapter: solid_cable
  connects_to:
    database:
      writing: cable
  polling_interval: 0.1.seconds
  message_retention: 1.day

The options are:

• connects_to - set the Active Record database configuration for the Solid Cable models. All options available in Active Record can be used here.
• polling_interval - sets the frequency of the polling interval. (Defaults to 0.1.seconds)
• message_retention - sets the retention time for messages kept in the database. Used as the cut-off when trimming is performed. (Defaults to 1.day)
• autotrim - sets wether you want Solid Cable to handle autotrimming messages. (Defaults to true)
• silence_polling - whether to silence Active Record logs emitted when polling (Defaults to true)
• use_skip_locked - whether to use FOR UPDATE SKIP LOCKED when performing trimming. This will be automatically detected in the future, and for now, you'd only need to set this to false if your database doesn't support it. For MySQL, that'd be versions < 8, and for PostgreSQL, versions < 9.5. If you use SQLite, this has no effect, as writes are sequential. (Defaults to true)
• trim_batch_size - the batch size to use when deleting old records (default: 100)

Trimming

Messages are autotrimmed based upon the message_retention setting to determine how long messages are to be kept around. If no message_retention is given or parsing fails, it defaults to 1.day. Messages are trimmed when a subscriber unsubscribes.

Autotrimming can negatively impact performance depending on your workload because it is doing a delete on ubsubscribe. If you would prefer, you can disable autotrimming by setting autotrim: false and you can manually enqueue the job later, SolidCable::TrimJob.perform_later, or run it on a recurring interval out of band.

License

The gem is available as open source under the terms of the MIT License.