message: [docs] CONTRIBUTING.md - how to setup SQL Lab in async mode
diff: @@ -52,6 +52,7 @@ little bit helps, and credit will always be given.
  - [Creating a new visualization type](#creating-a-new-visualization-type)
  - [Adding a DB migration](#adding-a-db-migration)
  - [Merging DB migrations](#merging-db-migrations)
  + - [SQL Lab Async](#sql-lab-async)
  ## Types of Contributions
  @@ -686,3 +687,29 @@ To fix it:
  ```bash
  superset db upgrade
  ```
  +
  +### SQL Lab Async
  +
  +It's possible to configure a local database to operate in `async` mode,
  +to work on `async` related features.
  +
  +To do this, you'll need to:
  +* Add an additional database entry. We recommend you copy the connection
  + string from the database labeled `main`, and then enable `SQL Lab` and the
  + features you want to use. Don't forget to check the `Async` box
  +* Configure a results backend, here's a local `FileSystemCache` example,
  + not recommended for production,
  + but perfect for testing (stores cache in `/tmp`)
  + ```python
  + from werkzeug.contrib.cache import FileSystemCache
  + RESULTS_BACKEND = FileSystemCache('/tmp/sqllab')
  + ```
  +
  +Note that:
  +* for changes that affect the worker logic, you'll have to
  + restart the `celery worker` process for the changes to be reflected.
  +* The message queue used is a `sqlite` database using the `SQLAlchemy`
  + experimental broker. Ok for testing, but not recommended in production
  +* In some cases, you may want to create a context that is more aligned
  + to your production environment, and use the similar broker as well as
  + results backend configuration
  