"Kevin Grittner" <kevin.gritt...@wicourts.gov> writes: > Robert Haas <robertmh...@gmail.com> wrote: >> The trouble is, AFAICS, that you can't bound M very well without >> scanning the whole table. I mean, it's bounded by theoretical >> limit, but that's it. > What would the theoretical limit be? (black size - page header size > - minimum size of one tuple) / item pointer size? So, on an 8KB > page, somewhere in the neighborhood of 1350?
Your math is off --- I get something less than 300, even if the tuples are assumed to be empty of data. (Header size 24 bytes, plus 4-byte line pointer, so at least 28 bytes per tuple, so at most 292 on an 8K page.) But you still end up probing just about every page for a 1% sample. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers