On Thu, Oct 21, 2021 at 4:29 PM Joe Conway <m...@joeconway.com> wrote: > meh -- the people who expect this to be impossibly fast don't typically > need or expect it to be exactly correct, and there is no way to make it > "exactly correct" in someone's snapshot without doing all the work.
I think it could actually be WAY faster than it is if, as Andres says, we had the ability to push the count operation inside the heap AM. I believe we have a tendency to attribute complaints like this to people have unreasonable expectations, but here I'm not sure the expectation is unreasonable. I vaguely recall writing a special-purpose code to count the number of tuples in relation years ago, and IIRC it was blazingly fast compared to letting our executor do it. I agree, however, that an approximation can be faster still. > That is why I didn't suggest making it the default. If you flip the > switch, you would get a very fast approximation. If you care about > accuracy, you accept it has to be slow. I'm not really here to take a position on the proposal. It doesn't excite me, because I have not run across any users in the combination of circumstances you mention: query can't be changed, exact answer not actually required, whole table being counted. But I am not here to call you a liar either. If you run across users in that situation all the time, then you do. -- Robert Haas EDB: http://www.enterprisedb.com
