On Mon, Jun 13, 2011 at 8:16 AM, Robert Haas <robertmh...@gmail.com> wrote:
> If the data type is hashable, you could consider building a hash table > on the MCVs and then do a probe for each element in the array. I > think that's better than the other way around because there can't be > more than 10k MCVs, whereas the input constant could be arbitrarily > long. I'm not entirely sure whether this case is important enough to > be worth spending a lot of code on, but then again it might not be > that much code. > Unfortunately, most time consuming operation isn't related to elements comparison. It is caused by complex computations in calc_distr function. > Another option is to bound the number of operations you're willing to > perform to some reasonable limit, say, 10 * default_statistics_target. > Work out ceil((10 * default_statistics_target) / > number-of-elements-in-const) and consider at most that many MCVs. > When this limit kicks in you'll get a less-accurate selectivity > estimate, but that's a reasonable price to pay for not blowing out > planning time. Good option. I'm going to add such condition to my patch. ------ With best regards, Alexander Korotkov.
