On Fri, Mar 25, 2022 at 5:00 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > > Robert Haas <robertmh...@gmail.com> writes: > > I vote for rejecting both of these patches. > > I see what James is on about here, but I agree that these specific changes > don't help much. What would actually be desirable IMO is a separate > section somewhere explaining the performance characteristics of ALTER > TABLE. (We've also kicked around the idea of EXPLAIN for ALTER TABLE, > but that's a lot more work.) This could coalesce the parenthetical > remarks that exist in ddl.sgml as well as alter_table.sgml into > something a bit more unified and perhaps easier to follow. In particular, > it should start by defining what we mean by "table rewrite" and "table > scan". I don't recall at the moment whether we define those in multiple > places or not at all, but as things stand any such discussion would be > pretty fragmented. > > regards, tom lane
I think a unified area discussing pitfalls/performance of ALTER TABLE seems like a great idea. That being said: given that "as things stand" that "discussion [already is] pretty fragmented" is there a place for a simpler improvement (adding a short explanation of this particular hazard) in the meantime? I don't mean this specific v4 patch -- just in general (since the patch can be revised of course). Thanks, James Coleman
