@ben.sless If you really need to optimize fetching stuff to the point that you can't use map->SomeRecordType, have you considered just writing your own low-level code to fetch the rows from the ResultSet in this case? I think that would be a little easier and faster than the big macro to reify RowBuilder and ResultSetBuilder. If you know what columns are coming back you can avoid the overhead of having to programatically figure that out via the ResultSetMetaData, the calls to read-column-by-index, etc. e.g.

(defrecord Person [id name])

(defn reducible-people-results [^java.sql.ResultSet rs]
  (reify
    clojure.lang.IReduceInit
    (reduce [_ rf init]
      (loop [acc init]
        (cond
          (reduced? acc) acc
          (.next rs)     (recur (rf acc (->Person
                                         (.getInt rs "id")
                                         (.getString rs "name"))))
          :else          acc)))))

(toucan2.conn/with-connection [conn :test/postgres]
  (with-open [stmt (.prepareStatement conn "SELECT id, name FROM people;")
              rset (.executeQuery stmt)]
    (reduce
     conj
     []
     (reducible-people-results rset))))
;; ->
[#Person{:id 1, :name "Cam"}
 #Person{:id 2, :name "Sam"}
 #Person{:id 3, :name "Pam"}
 #Person{:id 4, :name "Tam"}]