[tremon]

That's true, but now you have moved the goalposts. The original claim upthread was "it takes just as much work to delete a row as it takes to insert a row", not "it's hard to predict the performance of a delete with cascade effects". And the obvious rebuttal to that is that it's equally hard to provide an upper bound for the runtime of a single insert: an application cannot control the other processes running on the database, some of which may delay, interfere with or even invalidate your query and you must account for that. A delete operation is just as much "it might fail and you can retry" as an insert, or the database you're working with isn't ACID-compliant.

[fidotron]

> And the obvious rebuttal to that is that it's equally hard to provide an upper bound for the runtime of a single insert

This is precisely where you're going wrong. The insert is upper boundable in advance (you know the set of everything you might potentially have to insert), the delete isn't because you don't know what's in the db until you look.

I strongly recommend poking around with Foundation for this, because it becomes clear that this problem is the defining flaw with the way they tried to architect with layers, to the point they have a queuing system for processing large jobs of this type.

[ElectricalUnion]

> The insert is upper boundable in advance

A concurrent DML happening then suddenly your MERGE INTO WHEN NOT MATCHED INSERT/INSERT INTO SELECT is way larger that you thought? I thought "some workloads can suddenly be way larger that I expected" was supposed to be a thing in all non-trivial DML.