On Sat, Mar 28, 2020 at 8:02 PM James Coleman <jtc...@gmail.com> wrote: > > On Fri, Mar 27, 2020 at 9:24 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > Yeah, I also see this information could be useful. It seems Tom Lane > > is not entirely convinced of this. I am not sure if this is the right > > time to seek more opinions as we are already near the end of CF. So, > > we should either decide to move this to the next CF if we think of > > getting the opinion of others or simply reject it and see a better way > > for EXPLAIN to identify an index-only BMS. > > I'm curious if Tom's objection is mostly on the grounds that we should > be consistent in what's displayed, or that he thinks the information > is likely to be useless. >
Yeah, it would be good if he clarifies his position. > If consistency is the goal you might e.g., do something that just > changes the node type output, but in favor of changing that, it seems > to me that showing "how well did the optimization" is actually more > valuable than "did we do the optimization at all". Additionally I > think showing it as an optimization of an existing node is actually > likely less confusing anyway. > > One other thing: my understanding is that this actually matches the > underlying code split too. For the index only scan case, we actually > have a separate node (it's not just an optimization of the standard > index scan). There are discussions about whether that's a good thing, > but it's what we have. In contrast, the bitmap scan actually has it as > a pure optimization of the existing bitmap heap scan node. > I personally see those as valid points. Does anybody else want to weigh in here, so that we can reach to some conclusion and move ahead with this CF entry? -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com