> What's the verdict on relaxing the "live tuple's ctid doesn't 
> change rule"? If we did allow that within a page, what would 
> we need to change?

I already said this, but why would this need to be visible from the
outside ?

A few assumptions:
        no back pointers
        indexes only point at slots marked as roots (and non hot tuples)

During vacuum, you swap the tuples and keep a stub at the slot that the
user's ctid might be pointing at. You mark the stub to detect this
When a select/update by ctid comes along it needs to do one step to the
and use that tuple instead.

It needs a second vacuum (or a per page vacuum during update) to remove
extra stub when it is dead and not recently dead. 

I fail to see the hole.


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