Fix People Picker is Very Slow in SharePoint 2010

Problem: In a SharePoint 2010 environment, People picker is very slow! It takes more than 30 seconds to resolve any given users names in person or group fields.

SharePoint 2010 People Picker is too slow resolving

Solution:
Instruct people picker to search only within given AD domains! Here is how:

Set People Picker SearchADForest domains:
stsadm -o setproperty -pn peoplepicker-searchadforests -pv "domain:crescent.com" -url "https://portal.crescent.com"

If you have multiple domains, add ; as separators in PV parameter. E.g. "domain:Apac.crescent.com;domain:crescent.com" in 2 way trusted domains.

To get People Picker SearchADForest value applied:
Stsadm -o getproperty -pn peoplepicker-searchadforests -url "https://portal.crescent.com/"

To Clear People Picker SearchADForest values if exist already:
Stsadm -o getproperty -pn peoplepicker-searchadforests -pv "" -url "https://portal.crescent.com/"