# File lib/innodb/index.rb, line 9
  def initialize(space, root_page_number, record_describer=nil)
    @space = space
    @record_describer = record_describer || space.record_describer

    @root = page(root_page_number)

    unless @root
      raise "Page #{root_page_number} couldn't be read"
    end

    # The root page should be an index page.
    unless @root.type == :INDEX
      raise "Page #{root_page_number} is a #{@root.type} page, not an INDEX page"
    end

    # The root page should be the only page at its level.
    unless @root.prev.nil? && @root.next.nil?
      raise "Page #{root_page_number} is a node page, but not appear to be the root; it has previous page and next page pointers"
    end
  end