It does both. It's going to compute in real-time, unless you pre-compute by using a GenericUserSimilarity to precompute from a UserSimilarity implementation. Using a CachingUserSimilarity wrapper might be a smarter way to go.
Yes, this might be essential to respectable performance depending on your algorithm, DataModel, and data size. 2011/2/22 王世森 <[email protected]>: > Hi all, > > > > I`m a beginner in building recommendation system. I have a very simple > question, when we use mahout to do a CF recommendation, for example we use > the basic user-based recommendation, is the similarity between 2 users(or > the neighbourhood of one user) pre-computed or computed when the specific > recommendation is performed? > I found when I run the examples in mahout, the recommendation seems to be > performed in the latter way which makes it quite ineffective. Since I`m > doing a CF recommendation project, in which millions of users is involved so > I hope I can make the CF recommendation in a more effective way. > >
