On Thu, Feb 25, 2010 at 3:59 PM, Gokulakannan Somasundaram
<gokul007@gmail.com> wrote:
I disagree with that, Gokul -- if the ordering operators are volatile or just incorrect, during DELETE, you could set xmax in the wrong IndexTuple. Then there will be another IndexTuple that says it's visible, but it points to a non-visible heap tuple. I think you should follow the pointers to the heap before you decide to let an index tuple remain in the index during vacuum. This would ensure that all references from an index to a heap tuple are removed before vacuuming the heap tuple. I would be worried about what might break if this invariant doesn't hold.
First of all, volatility is not the only issue. The ordering ops could also be incorrect, e.g., violate the transitivity property. there is no reliable way to determine if a function is volatile and/or incorrectly specified.
Of course, PG can't "support" indexing with incorrect functions. However, it's worthwhile to guard against too much damage being done if the user's function has a bug. Maybe I'm wrong? Maybe an index tuple with a dangling pointer is actually harmless?
Karl
