On Mon, May 11, 2020 at 5:23 PM Alvaro Herrera <alvhe...@2ndquadrant.com> wrote:
> On 2020-May-11, Michel Pelletier wrote: > > > Is this asymmetry a bug? I realize these event trigger functions are > > typically written in C, but I'd like to keep this idea contained to a > > plpgsql function and cover as many reversible changes as I can. > > Sadly, you cannot obtain all the necessary details using only plpgsql. > The only way is to compile a C extension. There's a very rough, > incomplete skeleton to show how to do this in > src/test/modules/test_ddl_deparse. A much more complete approach, which > was not completed, was used to produce JSON output from the C > structures -- see > https://www.postgresql.org/message-id/20150409161419.gc4...@alvh.no-ip.org Ah thank you, test_ddl_deparse gives me a good idea what's going on now. Very interesting thread, thanks for your work on this. Keep in mind ALTER TABLE is a very sophisticated; you can do things like > ALTER TABLE one ADD COLUMN two INT, DROP COLUMN three, ADD COLUMN four > text; > (i.e. do several things in one command) so if you were to use a > simplistic approach, you might end up missing things. > This is a support feature for some users so they are encouraged to write down scripts. The idea being the tool would spit one out and they'll be advised to use it as a starting point for the actual post-hoc down script, so catching CREATE TABLE/INDEX is a good start. As this ddl deparsing feature evolves in the future, I can add more complex cases. Thanks again! -Michel > -- > Álvaro Herrera https://www.2ndQuadrant.com/ > PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services >
