Test Speed: ActiveRecord use_transactional_fixtures vs. DatabaseCleaner.strategy = :transaction
I spent a little time comparing the two on a mid-sized codebase that makes extensive use of ActiveRecord fixtures. When I switched it to use DatabaseCleaner instead of use_transactional_fixtures, the model specs started taking about twice the time.
After making the same comparisons you did, I realized that there are two things that use_transactional_fixtures controls:
- Whether each spec is wrapped in a transaction
- Where in the process the fixture data is loaded by ActiveRecord
- When
use_transactional_fixturesis true, the fixture data is loaded once, before the first test - When it is false, the fixture data is loaded before each spec
- When
DatabaseCleaner's transaction strategy can substitute for (1). But the downside is that your suite will repeatedly load the same fixture data.
So, if you don't use AR fixtures (or only use a couple), use_transactional_fixtures and DatabaseCleaner's transaction strategy will have similar performance. But if you use a lot of AR fixtures, turning use_transactional_fixtures off will have a big performance impact.