On 2018-02-27 16:58:11 -0500, Tom Lane wrote: > > 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. I'm fairly certain that only vacuum and table rewrites like cluster sets all-visible, and that there was never any released code that did so during SELECT. I think there were a few patches debating whether we could change that, but they never really got anywhere afair. Greetings, Andres Freund
