Re: Rename of triggers for partitioned tables

From: Arne Roland <A(dot)Roland(at)index(dot)de>
To: David Steele <david(at)pgmasters(dot)net>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Cc: Pg Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Rename of triggers for partitioned tables
Date: 2021-03-29 07:37:53
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David Steele wrote:
> Arne, thoughts on Álvaro's comments?
> Marking this patch as Waiting for Author.

Thank you for the reminder. I was to absorbed by other tasks. I should be more present in the upcoming weeks.

> I think you did not register the patch in commitfest, so I did that for
> you:

Thank you! I should have done that.

> As you say, triggers on children don't necessarily have to have the same
> name as on parent; this already happens when the trigger is renamed in
> the child table but not on parent. In that situation the search on the
> child will fail, which will cause the whole thing to fail I think.
> We now have the column pg_trigger.tgparentid, and I think it would be
> better (more reliable) to search for the trigger in the child by the
> tgparentid column instead, rather than by name.

The last patch already checks tgparentid and errors out if either of those do not match.
The reasoning behind that was, that I don't see a clear reasonable way to handle this scenario.
If the user choose to rename the child trigger, I am at a loss what to do.
I thought to pass it back to the user to solve the situation instead of simply ignoring the users earlier rename.
Silently renaming sounded a bit presumptuous to me, even though I don't care that much either way.

Do you think silently renaming is better than yielding an error?

> Also, I think it would be good to have
> to avoid recursing to children. This seems mostly pointless, but since
> we've allowed changing the name of the trigger in children thus far,
> then we've implicitly made it supported to have triggers that are named
> differently. (And it's not entirely academic, since the trigger name
> determines firing order.)

If it would be entirely academic, I wouldn't have noticed the whole thing in the first place.

The on only variant sounds like a good idea to me. Even though hardly worth any efford, it seems simple enough. I will work on that.

> Alternatively to this last point, we could decide to disallow renaming
> of triggers on children (i.e. if trigger has tgparentid set, then
> renaming is disallowed). I don't have a problem with that, but it would
> have to be an explicit decision to take.

I rejected that idea, because I was unsure what to do with migrations. If we would be discussing this a few years back, this would have been likely my vote, but I don't see it happening now.


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