Suppose I have a table and index: create table t(x int, y varchar, primary key(x)); and that the only updates are "update t set y = ... where x = ?". I understand that updating a row of t generates a new row version, and that different transactions may see different versions of the same row. How does versioning work for the index? - The update above does not update the index key. Does the index get updated at all? - If not, then how can an index lookup return the correct version of selected rows? This aspect of versioning has never been clear to me. Now there's a cost issue involved, as I need to update every row in a large table, never updating the index key. Will this run faster if I drop the index? (Yes, I can run the experiment, but I'd like to understand the fundamentals better.) Jack Orenstein
