"David G. Johnston" <david.g.johnston@xxxxxxxxx> writes: > If one runs vacuum on a table (small or otherwise) that is currently > choosing an index scan as its best plan how likely is it that post-vacuum > an index-only plan would be chosen if the index type and column presence > conditions are met? Offhand I think it would always prefer IOS over regular indexscan if the table is mostly all-visible. The problem in this example was that other choices dominate both. > Also, I recall discussion that select statements will touch the visibility > map (hence causing write I/O even in a read-only query) but [1] indicates > that only vacuum will set them ddl will clear them. Hm, I don't recall that, but I've not been involved in the last few rounds of hacking on that mechanism. regards, tom lane
