Hi, Josh, Josh Berkus wrote:
> Yes, actually. We need 3 different estimation methods: > 1 for tables where we can sample a large % of pages (say, >= 0.1) > 1 for tables where we sample a small % of pages but are "easily estimated" > 1 for tables which are not easily estimated by we can't afford to sample a > large % of pages. > > If we're doing sampling-based estimation, I really don't want people to lose > sight of the fact that page-based random sampling is much less expensive than > row-based random sampling. We should really be focusing on methods which > are page-based. Would it make sense to have a sample method that scans indices? I think that, at least for tree based indices (btree, gist), rather good estimates could be derived. And the presence of a unique index should lead to 100% distinct values estimation without any scan at all. Markus ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
