Re: Cost estimates for parameterized paths

Robert Haas <robertmhaas@gmail.com> writes:
> On Fri, Sep 3, 2010 at 2:04 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> On reflection I think that for parameterized paths the problem won't be
>> too bad, because (a) we'll ignore parameterized paths except when
>> considering a join to the right outer rel, so their presence in the
>> rel's pathlist won't cost much otherwise,

> Hmm.  Maybe they should go into a separate path list, and perhaps we
> could do the min/max calculations only with that pathlist (at least
> for now), thus avoiding taking a generalized penalty to handle this
> specific case.  IIUC, a parameterized path should never cause an
> unparamaterized path to be thrown out,

Yeah, but the converse isn't true.  I had considered the idea of keeping
parameterized paths in a separate list, but you'd still have to examine
the main list to look for unparameterized paths that might dominate them.
        regards, tom lane