> I hit an interestinhg paper on n_distinct calculation: > > http://www.pittsburgh.intel-research.net/people/gibbons/papers/distinct-values-chapter.pdf > > the PCSA algorithm described there requires O(1) calculation per > value. Page 22 describes what to do with updates streams. > > This I think (disclaimer: I know little about PG internals) means that > the n_distinct estimation can be done during vacuum time (it would > play well with the visibility map addon). > > What do You think? ok, if You think that calculating a has function of every data field for each insert or delete is prohibitive, just say so and don`t bother reading the paper :] Greetings Marcin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
