Serial data types and replication keys
You can use a serial data type as a replication key, but you must ensure that the values are unique across all replication servers.
If you plan to use serial data types (SERIAL, SERIAL8, or BIGSERIAL) as the replication key for a table, the same serial value might be generated on two servers at the same time. Use the CDR_SERIAL configuration parameter to generate non-overlapping values for serial columns across all database servers in your replication environment. Set CDR_SERIAL in the onconfig file for each primary source database server in the replication system.
You do not need to set the CDR_SERIAL configuration parameter if your replication key has multiple columns and the other columns identify the server on which each row is created.