On Fri, 2008-12-12 at 13:18 -0500, Tom Lane wrote: > I seem to recall Greg suggesting that there were ways to estimate > ndistinct without sorting, but short of a fundamental algorithm change > there's not going to be a win here.
Hash table? Haas Stokes suggests a Bloom filter. Why not keep the random algorithm we have now, but scan the block into a separate hash table for ndistinct estimation. That way we keep the correct random rows for other purposes. > > Right now we may as well use a random number generator. > > Could we skip the hyperbole please? Some of the ndistinct values are very badly off, and in the common cases I cited previously, consistently so. Once I'm certain the rescue helicopter has seen me, I'll stop waving my arms. (But yes, OK). -- Simon Riggs www.2ndQuadrant.com PostgreSQL Training, Services and Support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
