Stephen Frost <sfrost@xxxxxxxxxxx> writes: > I do wonder if we are maybe missing a bet at times though, considering > that I'm pretty sure we'll always go through the index in order, and > therefore randomly, even when we don't actually need the results in > order..? Has there been much consideration for just opening an index > and sequentially scanning it in cases like this where we have to go > through all of the index anyway and don't need the results in order? As I recall, it's unsafe to do so because of consistency considerations, specifically there's a risk of missing or double-visiting some entries due to concurrent index page splits. VACUUM has some way around that, but it doesn't work for regular data-fetching cases. (nbtree/README has more about this, but I don't feel like looking it up for you.) My guess based on your results is that the OP's table *isn't* all-visible, or at least the planner doesn't know it is. regards, tom lane
