# File lib/sup/ferret_index.rb, line 322
  def each_id query={}
    ferret_query = build_ferret_query query
    results = @index_mutex.synchronize { @index.search ferret_query, :limit => (query[:limit] || :all) }
    results.hits.map { |hit| yield @index[hit.doc][:message_id] }
  end