Re: Which SET TYPE don't actually require a rewrite

On Fri, Jul 17, 2020 at 11:26:56AM -0400, Tom Lane wrote:
> Magnus Hagander <magnus@hagander.net> writes:
> > As Amit mentions it is also triggered by some store parameter changes. But
> > not all. So looking at it the other way, the part that the end user really
> > cares about it "which ALTER TABLE operations will rewrite the table and
> > which will not". Maybe what we need is a section specifically on this that
> > summarizes all the different ways that it can happen.
> 
> No, what we need is EXPLAIN for DDL ;-).  Trying to keep such
> documentation in sync with the actual code behavior would be impossible.
> (For one thing, some aspects can be affected by extension datatype
> behaviors.)

I know Tom put a wink on that, but I actually do feel that the only
clean way to do this is to give users a way to issue the query in a
non-executing way that will report if a rewrite is going to happen.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

  The usefulness of a cup is in its emptiness, Bruce Lee