On Tue, Dec 19, 2017 at 11:14 PM, Greg Stark <stark@xxxxxxx> 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
