```ruby
require 'travis/config/heroku/url'

module Travis
  class Config
    class Heroku
      class Database < Struct.new(:options)
        include Helpers

        VARIABLES = { application_name: ENV['DYNO'] || $0, statement_timeout: 10_000 }
        DEFAULTS  = { adapter: 'postgresql', encoding: 'unicode', variables: VARIABLES }

        def config
          config = compact(Url.parse(url).to_h)
          config = deep_merge(DEFAULTS, config) unless config.empty?
          config[:pool] = pool.to_i if pool
          config
        end

        private

          def url
            env('DATABASE_URL').compact.first
          end

          def pool
            env('DATABASE_POOL_SIZE', 'DB_POOL').compact.first
          end

          def env(*keys)
            ENV.values_at(*keys.map { |key| prefix(key) }.flatten)
          end

          def prefix(key)
            key = [options[:prefix], key].compact.join('_').upcase
            ["TRAVIS_#{key}", key]
          end

          def options
            super || {}
          end
      end
    end
  end
end
```

Use PGBOUNCER_PREPARED_STATEMENTS env var to control prepared statements
user
```ruby
require 'travis/config/heroku/url'

module Travis
  class Config
    class Heroku
      class Database < Struct.new(:options)
        include Helpers

        VARIABLES = { application_name: ENV['DYNO'] || $0, statement_timeout: 10_000 }
        DEFAULTS  = { adapter: 'postgresql', encoding: 'unicode', variables: VARIABLES }

        def config
          config = compact(Url.parse(url).to_h)
          config = deep_merge(DEFAULTS, config) unless config.empty?
          config[:pool] = pool.to_i if pool
          config[:prepared_statements] = prepared_statements != 'false' if prepared_statements
          config
        end

        private

          def url
            env('DATABASE_URL').compact.first
          end

          def pool
            env('DATABASE_POOL_SIZE', 'DB_POOL').compact.first
          end
          
          def prepared_statements
            env('PGBOUNCER_PREPARED_STATEMENTS').compact.first
          end

          def env(*keys)
            ENV.values_at(*keys.map { |key| prefix(key) }.flatten)
          end

          def prefix(key)
            key = [options[:prefix], key].compact.join('_').upcase
            ["TRAVIS_#{key}", key]
          end

          def options
            super || {}
          end
      end
    end
  end
end
```
assistant