Re: Adding a stored generated column without long-lived locks

On Fri Apr 24, 2026 at 2:10 AM PDT, Alberto Piai wrote:
> On Tue Apr 7, 2026 at 5:02 PM +08, Alberto Piai wrote:
>> On Tue Mar 17, 2026 at 5:31 PM +07, Alberto Piai wrote:
>>
>>> I recently needed to add a stored generated column to a table of
>>> nontrivial size, and realized that currently there is no way to do
>>> that without rewriting the table under an AccessExclusiveLock.

The attached v4 is a rebase against current master, plus:

- I moved the call to RememberAllDependentForRebuilding before the
  update to pg_attribute, since it provides checks for some
  invalid/unsupported invocations it seems more useful to do it before
  changing anything.

- I hadn't noticed before that AddRelationNewConstraints returns the new
  (cooked) default definitions, so we can use those instead of building
  them again.

- cleaned up some includes I had added by mistake, and moved some tests
  around between the two commits

A while back I also posted a fix for the issue of DROP EXPRESSION not
working with subpartitions [1], this patch isn't ajusted yet to match, I
would do that if the bugfix would be committed first.

I am still hoping to get a reviewer for the in-person commitfest at the
upcoming pgconf.dev :)

It's my first contribution, but the change is pretty self-contained and
hopefully not terribly complex to review. I'm trying to address a real
world use case, it would be fantastic to make some progress with this
patch.

Anyone's motivated? :)


Regards,

Alberto


[1] https://www.postgresql.org/message-id/DHMT78XOD8BK.341V3H87KZ7NO%40gmail.com


-- 
Alberto Piai
Sensational AG
Zürich, Switzerland