I just did a clean install of OSX Mavericks, after migrated important via Migration Assistant, the mdworker on OSX Mavericks is busy indexing stuff.
You will see a bunch of mdworker(s) doing their work in Activity Monitor
If you want to find out what are mdworker(s) working on, can try this command in the terminal
$ sudo fs_usage -w -f filesys mdworker
If you found out there are folders you don’t want Spotlight to index, can add it into Privacy tab on Spotlight’s preference.
Enjoy!