Re: pgsql: Prevent tuples to be marked as dead in subtransactions on standb

On Tue, Dec 19, 2023 at 03:15:42PM -0500, Robert Haas wrote:
> I don't think this is a good commit message. It's totally unclear what
> it means, and when I opened up the diff to try to see what was
> changed, it looked nothing like what I expected.

(Not my intention to ignore you here, my head has been underwater for
some time.)

> I think a better message would have been something like
> "startedInRecovery flag must be propagated to subtransactions".

You are right, sorry about that.  Something like "Propagate properly
startedInRecovery in subtransactions started during recovery" would
have been better than what I used.

> And I
> think there should have been some analysis in the commit message or
> the comments within the commit itself of whether it was intended that
> this be propagated to subtransactions or not. It's hard to understand
> why the flag would have been placed in the TransactionState if it
> applied globally to the transaction and all subtransactions, but maybe
> that's what happened.

Alvaro has mentioned something like that on the original thread where
we could use comments when a transaction state is pushed to a
subtransaction to track better the fields used and/or not used.
Documenting more all that at the top of TransactionStateData is
something we should do.

> Instead of discussing that issue, your commit message focuses in the
> user-visible consequences, but in a sort of baffling way. The
> statement that "Dead tuples are ignored and are not marked as dead
> during recovery," for example, is clearly false on its face. If
> recovery didn't mark dead tuples as dead, it would be completely
> broken.

Rather than "dead" tuples, I implied "killed" tuples in this sentence.
Killed tuples are ignored during recovery.
--
Michael