Mapper and TableMapper performance is poor with large output records #1620
Description
When there are lots of identical mappings and/or constant values, each row iterated is processed one field at a time, which is inefficient and slow
Furthermore the bulk insert / upsert capabilities of TableMapper are much slower due to the fact that each row and each field must be processed individually.
see: https://docs.google.com/spreadsheets/d/1pTsV3mXZ6M0EUlszswMUdEdWEtiaEgxrwXmLQ7VM65A/edit#gid=0