Hi, On 2026-04-29 10:07:04 +0200, Hannu Krosing wrote: > On Wed, Apr 29, 2026 at 5:39 AM Dilip Kumar <[email protected]> wrote: > > > I am trying to understand your idea. If we are trying to deparse from > > an actual system table using a snapshot, why don't we just use the > > WAL? I mean, the WAL should contain the actual catalog modifications > > it has made. > > We have the full data in the catalog and we would likely need catalog > queries for any change, even when de-parsing the tree. > > And we should not add the extra load on the original DDL side, just as > we don't for DML.
That can't be a relevant cost compared to everything else. > At most we could just serialize the statement tree into the WAL, > though even that may be an overkill if we can get the change from > existing records. > > - insert new row in pg_class --> extract the CREATE TABLE (or INDEX, or ...) > - update row in pg_class or insert, update or delete a row in > pg_attribute --> extract ALTER TABLE > - except when it just updates relfilenod --> extract TRUNCATE > - delete row in pg_class --> DROP TABLE > - dml on pg_constraint --> ALTER TABLE > > ... etc That doesn't work in the general case, think of ALTER TABLE ... ALTER COLUMN ... TYPE foo USING (...) There's a big difference between USING(foo::int8) and USING (pg_size_bytes(foo)) but it's nowhere visible in the WAL. Greetings, Andres Freund
