On Tue, Feb 12, 2019 at 11:58 AM Jeff Janes <jeff.ja...@gmail.com> wrote:
> > On Tue, Feb 12, 2019 at 10:42 AM Tom Lane <t...@sss.pgh.pa.us> wrote: > >> >> Hm. blcostestimate is using the default cost calculation, except for >> >> /* We have to visit all index tuples anyway */ >> costs.numIndexTuples = index->tuples; >> >> which essentially tells genericcostestimate to assume that every index >> tuple will be visited. This obviously is going to increase the cost >> estimate; maybe there's something wrong with that? >> > > I assumed (without investigating yet) that genericcostestimate is applying > a cpu_operator_cost (or a few of them) on each index tuple, while the > premise of a bloom index is that you do very fast bit-fiddling, not more > expense SQL operators, for each tuple and then do the recheck only on what > survives to the table tuple part. > In order for bloom (or any other users of CREATE ACCESS METHOD, if there are any) to have a fighting chance to do better, I think many of selfuncs.c currently private functions would have to be declared in some header file, perhaps utils/selfuncs.h. But that then requires a cascade of other inclusions. Perhaps that is why it was not done. Cheers, Jeff >
