With combined point/range key iteration, we often find ourselves checking for changes to the range key by comparing the bounds to a previous range key, and then caching the range key stack. Something like:

if hasPoint, hasRange := iter.HasPointAndRange(); hasRange {
	if rangeBounds := iter.RangeBounds(); !rangeBounds.Key.Equal(rangeStart) {
		rangeStart = append(rangeStart[:0], rangeBounds.Key...)
		iter.RangeKeys().CloneInfo(&rangeKeys)

These constant key comparisons are expensive. Furthermore, it would be nice if it was safe to reuse the range key stack as long as the keys didn't change, so we wouldn't have to clone it.

This depends on cockroachdb/pebble#1775.

Jira issue: CRDB-17624

Epic CRDB-2624