Re: A thought on Index Organized Tables

On Thu, Feb 25, 2010 at 3:59 PM, Gokulakannan Somasundaram <
gokul007(at)gmail(dot)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.
>>
>
> Well, Karl, if we have to support function based indexes/IOT, one thing is
> for sure. We can't support them for volatile functions / broken data types.
> Everyone agrees with that. But the question is how we identify something is
> not a volatile function. Only way currently is to let the user make the
> decision( Or we should consult some mathematician ). So we need not consult
> the heaptuple.
>
>
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