On Mon, 10 Dec 2018 at 16:14, Alvaro Herrera <alvhe...@2ndquadrant.com> wrote:
> Hi Greg > > On 2018-Dec-07, Greg Stark wrote: > > > I'm thinking I should try to move all these decisions to phase 1 as > > much as possible but I'm not sure how feasible it will be to get the > > results exactly correct. Of course the cases where it's hardest to > > predict are precisely where users would most like to know what's going > > to happen... > > Maybe you can move some of these decisions to phase 1, but I'm not sure > it can be done for all of them. Another possible plan is to add a flag > "dry run" so that phases 2/3 do whatever analysis they need to report > for your EXPLAIN, but not actually carry out their tasks. (I see two > options to implement this, one is a global flag and the other is a new > argument to all those routines.) > You need to take a table lock to find out things about the table. EXPLAIN seems like the wrong place for this. I suggest ALTER TABLE should respond to a parameter setting of ddl_dry_run = on, so the whole world doesn't need to rewrite its syntax to support the new option. -- Simon Riggs http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
