…may be symptoms after upgrading to a new Mac OS. It is usually related to Spotlight indexing your Mac and may take several hours (the older your Mac, the longer it takes). If you’re getting nervous, open Activity Monitor (in the Utilities folder) and check the CPU load (select all processes). If “mds” and “mdworker” are the ones causing the work load everything is fine. Let them be! If not, follow this hint.