Re: benchmarking the query planner

>
>
> > Do you consider using hash tables?
>
> Doubt it's really worth it, unless there's some way to amortize the
> setup cost across multiple selectivity estimations; which would surely
> complicate life.
>
MCV lists are updated only during "analyze" phase, don't they? If the "setup
cost" is the cost of maintaining those "hash tables", it is not going to
hurt much.

>
> One thing that just now occurred to me is that as long as we maintain
> the convention that MCV lists are in decreasing frequency order, one can
> take any prefix of the list and it's a perfectly good MCV list of less
> resolution. So one way to reduce the time taken in eqjoinsel is to set
> an upper limit on the number of entries considered *by that routine*,
> whereas other estimator functions could use larger lists.

That makes sense, however, linear search for single item in the list of
10'000 elements could take a while. Hash lookup might be better choice.

Regards,
Vladimir Sitnikov