clear_stale_cached_connections!

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 206
      def clear_stale_cached_connections!
        keys = @reserved_connections.keys - Thread.list.find_all { |t|
          t.alive?
        }.map { |thread| thread.object_id }
        keys.each do |key|
          conn = @reserved_connections[key]
          ActiveSupport::Deprecation.warn(Database connections will not be closed automatically, please close yourdatabase connection at the end of the thread by calling `close` on yourconnection.  For example: ActiveRecord::Base.connection.close) if conn.in_use?
          checkin conn
          @reserved_connections.delete(key)
        end
      end