Alvaro Herrera <alvhe...@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 -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers