スキーマ: Terms
    ...
    schema.create_table("Terms",
                        :type => :patricia_trie,
                        :key_type => "ShortText",
                        :default_tokenizer => "TokenBigram",
                        :key_normalize => true) do |table|
      table.index("Messages.subject")
      table.index("Messages.body")
    end
  end