Note that on the Github repo for this benchmark, the README mentions that: "... later versions will include a complete range of workloads (including deleting,

Note that on the Github repo for this benchmark, the README mentions that: "... later versions will include a complete range of workloads (including deleting, updating, appending, and complex select operations) and they will also evaluate multi-server configurations." Any update in PostgreSQL will result in a new tuple being inserted, whether it contains json, hstore or anything else; that's the basis of multi-version concurrency control. It'll be the same deal with jsonb. Not only that, the delta to update the page to contain the new tuple, and a copy of the full page the tuple is being written to (if it's the first change to that page in that checkpoint cycle) are written to the write-ahead log.