def stats(type = nil)
      type = nil unless ALLOWED_STAT_KEYS.include? type
      values = {}
      ring.servers.each do |server|
        values[server.name.to_s] = server.alive? ? server.request(:stats, type.to_s) : nil
      end
      values
    end
#
Collect the stats for each server.
You can optionally pass a type including :items, :slabs or :settings to get specific stats
Returns a hash like { 'hostname:port' => { 'stat1' => 'value1', ... }, 'hostname2:port' => { ... } }