deadlock detected with capybara-webkit

Question

I'm trying to pass this spec : ``` scenario "Edit a service", js: true do service = create_service_for(provider, title: "First service") fill_edit_service_form(service) expect(page).to have_css('#price', text: '10,00 $') end ``` This is a standard rails spec using capybara. I am using capybara-webkit for all scenario with javascript. When I'm trying to pass it, sometimes it works, sometimes it mark than there is a missing record in the database and sometime I have this error : ``` Run options: include {:locations=>{"./spec/acceptances/provider_services_spec.rb"=>[31]}} [K 1) Provider Services Edit a service Failure/Error: Unable to find matching line from backtrace ActiveRecord::StatementInvalid: PG::TRDeadlockDetected: ERROR: deadlock detected DETAIL: Process 24164 waits for AccessExclusiveLock on relation 3446991 of database 3446538; blocked by process 24184. Process 24184 waits for AccessShareLock on relation 3446902 of database 3446538; blocked by process 24164. HINT: See server l…

Accepted Answer

This is happening because you have two threads, the test and the request, modifying the database asynchronously. It looks like you've rightly been experimenting with different configurations in your spec_helper. I've spend a fair amount of time struggling with this same issue, and have come up with this:

```
# adapted from https://gist.github.com/moonfly/4950750

require 'database_cleaner'

RSpec.configure do |config|

config.use_transactional_fixtures = false

config.before( :suite ) do
    DatabaseCleaner.clean_with :truncation
    DatabaseCleaner.strategy = :transaction
  end

config.around( :each ) do |spec|
    if spec.metadata[:js]
      # JS => doesn't share connections => can't use transactions
      spec.run
      DatabaseCleaner.clean_with :deletion
    else
      # No JS/Devise => run with Rack::Test => transactions are ok
      DatabaseCleaner.start
      spec.run
      DatabaseCleaner.clean

# see https://github.com/bmabey/database_cleaner/issues/99
      begin
        ActiveRecord::Base.connection.send :rollback_transaction_records, true
      rescue
      end
    end
  end

end
```

I keep it all in support/database_cleaner_configuration.rb, which would work for you, as well, or you can simply replace what you've got in your spec_helper. If this doesn't work, let me know - I have a few other ideas, but they're kookier, and not worth getting into if this works, which it probably will...

Note:

It might be worth mentioning that Rails 5.1+ solves the database problem. Eileen Uchitelle on the Rails team made the changes necessary to run ensure test threads and the Rails server can run in the same process by sharing the database connection.

deadlock detected with capybara-webkit

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