Re: Postgres upgrade 12 - issues with OIDs

On Mon, 28 Nov 2022 at 12:46, Venkata B Nagothi <nag1010(at)gmail(dot)com> wrote:
> Coming back to this thread after a while.. we have to remove OID on a 6 TB (5 TB of indexes) table and ALTER TABLE is gonna block the table and is gonna take hours...

You may want to look into exploiting table inheritance for this.
Something like:

create table tab (a int, b int) with oids; -- the existing table

begin; -- do make the following atomic
alter table tab rename to old_tab;
create table tab (a int, b int) without oids; -- new version of the
table, without oids
alter table old_tab inherit tab; -- make it so querying the new table
also gets rows from the old table.
commit;

-- do this a bunch of times over the course of a few days until
old_tab is empty.
with del as (delete from old_tab where a in (select a from old_tab
limit 1000) returning *) insert into tab select * from del;

you can then drop the old table.

You'll need to think carefully about unique constraints and any other
constraints which are on the table in question. You'll want to do a
lot of testing before committing to doing this too.

David