The current IteratorStats count seeks and steps. There is a desire to also include the total bytes encountered, since rows can be big. We could expose two things:

• [A] Cumulative key+value size for each position the Iterator was at (this could be calculated by the caller, but probably better in the lower layer).
• [B] Cumulative bytes in blocks that were loaded using sstable.Reader.readBlock.

This desire is mentioned

• as a bullet in storage: track iteration stats per engine.Iterator cockroach#59069 (comment)
• implied in an internal conversation with @andreimatei "if anyone ends up doing more work in the area, I've got a feature request for ya - I want data on the size of the skipped garbage".
  • Pebble is not concerned with what is "skipped" by the MVCC layer, but by exposing A and B, we can know that B-A was wasted. Though such waste may not have been costly if it hit the block cache.