On Fri, Apr 24, 2020 at 2:42 PM Andy Fan <zhihui.fan1...@gmail.com> wrote: >> >> >> > 3. I added the material path in a very hacked way, the if check just to >> > make >> > sure it take effect on my test statement only. If you want to test this >> > patch locally, >> > you need to change the oid for your case. >> > >> > + if (linitial_node(RangeTblEntry, root->parse->rtable)->relid == >> > 25634) >> > + best_path = (Path *) create_material_path(final_rel, >> > best_path); >> >> Can we just directly add the material path on top of the best path? I >> mean there are possibilities that we might not get any benefit of the >> material because there is no duplicate from the outer node but we are >> paying the cost of materialization right? The correct idea would be >> that we should select this based on the cost comparison. Basically, >> we can consider how many duplicates we have from the outer table >> variable no? > > > Thanks for interesting of it. Of course we can't add the material path on > best path, > that's why I say it is a very hacked way. and say "how to cost this > strategy is > challenge " (the part you striped when you reply the email).
Right, I see that now. Thanks for pointing it out. But we have to > test a path first (it must be helpful on some case at least) and the result > is correct, > then we think about how to cost it. The purpose of my writing is about the > first step > and see what people think about it. Ok > > As for how to cost it, I'm agreed with your suggestion, but we may need more > than that, like. (1, 2, 1) and (1, 1, 2) is same for your suggestion, but > they > are not different in this path. Valid point. -- Regards, Dilip Kumar EnterpriseDB: http://www.enterprisedb.com
