Trivial Description
The constructor for IndexRowToBaseRowResultSet
takes a bitset describing the columns coming from the heap and a
bitset describing the columns coming from the index. But in every
IndexRowToBaseRowResultSet one also has to compute all referenced
columns (union of heap and index bitsets), and frequently also those
columns only coming from the heap (set difference between heap and
index).
But the value of these "set products" seem only to depend on objects
that are fixed at compile time (in IndexToBaseRowNode), so it would be
cleaner (and possibly more efficient) to compute these products there.