On Wed, Feb 29, 2012 at 1:40 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: >> I am having trouble >> constructing an example, but I feel like there might be cases where >> it's possible to have path A, not parameterized, path B, parameterized >> by R, and path C, parameterized by S, and maybe also path D, >> parameterized by both R and S. In that case, I feel like paths B and >> C are incomparable. > > Indeed, and the code already knows that. However, in this example, path > A is capable of dominating the other three (being strictly less > parameterized than them), and B and C are each capable of dominating D. > The problem is just that I'd neglected to consider that rowcount now > also becomes a figure of merit.
In theory, yes, but in practice, won't it nearly always be the case that a less parameterized path generates more rows, and a more parameterized path generates less rows, so that neither dominates the other? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
