The fetch methods for row blocks are _fetch_into_extfn and _fetch_block_extfn. These methods are part of the a_v4_extfn_table_func structure.
When producing data, if the table UDF or TPF builds its own row block, the UDF must provide the fetch_block API method. If the UDF does not build its own row block, the UDF must provide the fetch_into API method.
When consuming data, if the TPF builds its own row block, the UDF calls the fetch_into method on the producer. If the TPF does not build its own row block, the TPF must call the fetch_block method on the producer.
The UDF can select which fetch method to use for data production and consumption. In general, these guidelines apply: