Re: Group-count estimation statistics

Manfred Koizar <mkoi-pg@aon.at> writes:
> On Fri, 28 Jan 2005 10:53:33 -0500, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> we should consider
>> something like "clamp to size of table / 10" instead.

> ... unless a *single* grouping column is estimated to have more than
> N/10 distinct values, which should be easy to check.

Already done that way.

            /*
             * Clamp to size of rel, or size of rel / 10 if multiple Vars.
             * The fudge factor is because the Vars are probably correlated
             * but we don't know by how much.
             */
            double        clamp = rel->tuples;

            if (relvarcount > 1)
                clamp *= 0.1;
            if (reldistinct > clamp)
                reldistinct = clamp;


            regards, tom lane