Improve your data upload time when using the external data API by loading CSV files incrementally. By registering data faster, you can bring in more data to your existing datasets without causing the overall run time to grow exponentially.
Where: This change applies to CRM Analytics in Lightning Experience and Salesforce Classic. CRM Analytics is available in Developer Edition and for an extra cost in Enterprise, Performance, and Unlimited editions.
How: When using the Analytics External Data API to load data, set the mode to incremental.
Append Data Faster with Incremental Uploads (Generally Available) (salesforce.com)