> > * Is this feature useful? Is there a possibility it will be accepted? > > I think adding such information to EXPLAIN outputs is useful because it will > help users > confirm the effect of a multicolumn index on a certain query and decide to > whether > leave, drop, or recreate the index, and so on.
Thank you for your comments and for empathizing with the utility of the approach. > > * Are there any other ideas for determining if multicolumn indexes are > > > > being used efficiently? Although I considered calculating the > > efficiency using > > > > pg_statio_all_indexes.idx_blks_read and > > pg_stat_all_indexes.idx_tup_read, > > > > I believe improving the EXPLAIN output is better because it can be > > output > > > > per query and it's more user-friendly. > > It seems for me improving EXPLAIN is a natural way to show information on > query > optimization like index scans. OK, I'll proceed with the way. > > * Is "Index Bound Cond" the proper term?I also considered changing > > > > "Index Cond" to only show quals for the boundary condition and adding > > > > a new term "Index Filter". > > "Index Bound Cond" seems not intuitive for me because I could not find > description > explaining what this means from the documentation. I like "Index Filter" that > implies the > index has to be scanned. OK, I think you are right. Even at this point, there are things like ‘Filter’ and ‘Rows Removed by Filter’, so it seems natural to align with them. I described a new output example in the previous email, how about that? > > * Would it be better to add new interfaces to Index AM? Is there any > > case > > > > to output the EXPLAIN for each index context? At least, I think it's > > worth > > > > considering whether it's good for amcostestimate() to modify the > > > > IndexPath directly as the PoC patch does. > > I am not sure it is the best way to modify IndexPath in amcostestimate(), but > I don't > have better ideas for now. OK, I’ll consider what the best way to change is. In addition, if we add "Rows Removed by Index Filter", we might need to consider a method to receive the number of filtered tuples at execution time from Index AM. Regards, -- Masahiro Ikeda NTT DATA CORPORATION
