You have already been informed. PG, as yet, does not allow incremental refresh of a MV. It allows online refresh of a MV, but that it does by doing a full table scan of the base table and rebuilding the MV.
Materialized view log is one of the feature in oracle. It creates a log in which the changes made to the table are recorded. This log is required for an asynchronous materialized view that is refreshed incrementally.
I read in the below link about incrementally refreshing the materialized view in postgresql: