When you create a Replication Agent instance, you can choose to enable supplemental logging of primary key (PK) and unique index (UI) columns at the table level.
Supplemental logging at database level is not essential for Replication Agent while replicating. Instead, you can enable supplemental logging of PK and UI columns at table level for the Oracle system tables and user tables that need to be replicated. After you enable supplemental logging of PK and UI columns at table level, Oracle writes the columns of PK and UI to the redo log file, whenever the table is updated. This reduces the size of redo log file compared to supplemental logging of PK and UI at database level. For a table whose supplemental logging is not enabled, Oracle writes columns of PK and UI to the redo log file, only when any column of PK or UI is updated.