Re: Document atthasmissing default optimization avoids verification table scan

Robert Haas <robertmhaas@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