wher can I find such infos about indices?
I am not exactly sure if this is special topic documented in the man pages or the admin guide but it was discussed multiple time here on this list, so you should be able to find it in the archives.
-Quanah
-- Quanah Gibson-Mount Principal Software Developer ITSS/Shared Services Stanford University GnuPG Public Key: http://www.stanford.edu/~quanah/pgp.html