What locks are taken during statistic operations in SQL Server?
AFAIK, the only real X lock that is taken is on the 'statistics resource'.  The rest of the locks can be read around and don't block.


  That is a resource that only statistics operations care about. It
  exists to limit the number of stats operations in progress on a single
  table to one at a time. Auto-statistics operations do not wait for it
  but just abort if they cannot get it. Manual statistics operations do
  wait for the resource.


https://connect.microsoft.com/SQLServer/feedback/details/174619/update-statistics-holding-exclusive-lock-and-blocking