Parametric Search Appliance
The default Rewalk Type, a New walk behaves just like the initial walk.
The Parametric Search Appliance creates a new database and does a complete walk of
everything, starting with the Base URLs. A New walk does not disturb the
existing database during the walk.
New walks - New walks are useful when
first setting up a profile and changing walk settings, as you're guaranteed to
see your setting changes reflected in each document when a walk finishes. If
you later make significant walk setting changes, it is recommended to do a
New walk to make sure your indexed data reflects your new settings.
Once your settings are established, though, fully processing every URL on every walk can be inefficient, and a different walk type may be more appropriate.