Primary index in Teradata - forum topic by Sunikutty

I am a beginner in teradata.
I read that PI is used in data distribution in teradata and unline Primary key value in PI column can be udpated.If columns in which PI is defined gets updated  then wont that result in data re-distribution across AMPS, which might make my update query run long?
If PI is defined on multiple columns hash value to decide on AMP number will be applied on both columns on which PI is defined is it?