Jeff Janes <jeff.ja...@gmail.com> writes: > So even though it knows that 6952 values have been shoved in the bottom, it > thinks only 200 are going to come out of the aggregation. This seems like > a really lousy estimate. In more complex queries than the example one > given it leads to poor planning choices.
> Is the size of the input list not available to the planner at the point > where it estimates the distinct size of the input list? I'm assuming that > if it is available to EXPLAIN than it is available to the planner. Does it > know how large the input list is, but just throw up its hands and use 200 > as the distinct size anyway? It does know it, what it doesn't know is how many duplicates there are. If we do what I think you're suggesting, which is assume the entries are all distinct, I'm afraid we'll just move the estimation problems somewhere else. I recall some talk of actually running an ANALYZE-like process on the elements of a VALUES list, but it seemed like overkill at the time and still does. regards, tom lane -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers