When I use airbyte to ingest say a BigQuery/Postgres table and define a cursor field on it to fetch incremental records every 5min. Does airbyte scan the entire table to identify new records ? Is it on me to define an index on the cursor table so that airbyte can quickly identify the new records ?

No it will send a query only to select new records

@Marcos Marx (Airbyte) thanks for the response. I understand the query will only select new records, but the execution of the query will run over all records right? So if I have a billion rows with new rows being constantly added in bigquery. I have to pay the cost of scanning the entire big query table every 5 min? Am I missing something? Or will this be prohibitively expensive?