On 19 December 2017 at 10:00, Oleksandr Shulgin <oleksandr.shulgin@xxxxxxxxxx> wrote: > If there would be an option in the database itself to provide those > estimation, we wouldn't even need to figure out estimation queries. > "EXPLAIN CREATE INDEX" anyone? 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. I'm not clear how you would determine how much memory is needed to sort a table without actually doing the sort though. So that would be more of an EXPLAIN ANALYZE wouldn't it? -- greg
