Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> [ ... a large amount of analysis based on exactly one test case ... ]
I think you are putting too much emphasis on fixing one case and not
enough on considering what may happen in other cases ...
In general, estimating n-distinct from a sample is just plain a hard
problem, and it's probably foolish to suppose we'll ever be able to
do it robustly. What we need is to minimize the impact when we get
it wrong. So I agree with the comment that we need to finish the
unfinished project of making HashAggregate tables expansible, but
I'm dubious about the rest of this.
regards, tom lane