On Tue, Dec 19, 2017 at 11:14 PM, Greg Stark <stark@mit.edu> wrote:
> You're not the first to propose something like that. I think an
> EXPLAIN ALTER TABLE would also be very handy -- it's currently
> impossible to tell without carefully reading the source code whether a
> given DDL change will require a full table scan, a full table rewrite,
> or just a quick meta data update (and even in that case what strength
> lock will be required). I think there are other utility statements
> that make interesting heuristic decisions that would be nice to be
> able to have some visibility into -- CLUSTER comes to mind.
An application of such things is attempting to estimate the amount of
disk space needed when doing a schema upgrade, so that could be handy.
--
Michael