Robert Haas <robertmh...@gmail.com> writes: > I don't object to the feature, but I think it's real-world utility > will be more limited than we might hope. When covering indexes are > not in play, someone might choose to index only, say, the primary key. > And maybe the primary key doesn't change very often, so HOT still > applies to nearly all updates. But then when they try to make a > covering index, they're now indexing columns that they *do* update > pretty regularly. Now the gain from index-only scans is fighting with > the loss from some updates no longer being HOT. I think in many cases > losing the benefit of HOT will cost more than the covering index > gains, at least in 9.2. I hope we'll be able to improve it in future > releases.
Well, if the table is getting enough update traffic that it matters much whether your updates are HOT or not, then index-only scans are probably a dead letter anyhow, because too small a fraction of the pages will be all-visible. I think the IOS feature is only good for something on read-mostly tables. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers