Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> Amit Kapila wrote:
>> Will the column store obey snapshot model similar to current heap tuples,
>> if so will it derive the transaction information from heap tuple?
> Yes, visibility will be tied to the heap tuple -- a value is accessed
> only when its corresponding heap row has already been determined to be
> visible. One interesting point that raises from this is about vacuum:
> when are we able to remove a value from the store? I have some
> not-completely-formed ideas about this.
Hm. This seems not terribly ambitious --- mightn't a column store
extension wish to store tables *entirely* in the column store, rather
than tying them to a perhaps-vestigial heap table? Perhaps that's a
necessary restriction to get to something implementable, but considering
that the proposal mentions pluggable column stores I should think you'd
not want to tie it down that much.
I can't help thinking that this could tie in with the storage level API
that I was waving my arms about last year. Or maybe not --- the goals
are substantially different --- but I think we ought to reflect on that
rather than just doing a narrow hack for column stores used in the
particular way you're describing here.
regards, tom lane
