portsdb -Uu

[ke han]

I am using
portsnap fetch
portsnap update

to sync my ports tree on FreeBSd 6.1...it seems it maintains an index  
when I run update.

I am used to using:
portsversion and portsupdate to upgrade ports...in this method I have  
also used
portsdb -Uu
to rebuild an index anytime prior to running these commands...yes  
portsdb takes a while and I've always wondered if this is necessary  
prior to running any of these commands..

So my question is:  Is the index being maintained by portsnap the  
same or a replacement to that used by portupgrade?  Do I have to  
maintain both sets of indexes in order to use portsupdate??
What do other people do?

thanks, ke han