There are two approaches to refresh an Extract-> Full Refresh and Incremental Refresh
Full Refresh->
As the name says the Extract will be fully refreshed. All the data/rows in the Extract will be completely replaced by the new data/rows from the data source.
This is the default refresh.
Depending on the number of records we fetch, it may sometime be expensive on the data source and may take long time.
Incremental Refresh->
Rather than refreshing the entire extract, we can set it up to only add the rows that are new since the last time we extracted data. For example, we may have a data source that is updated daily with new sales transactions. Rather than rebuild the entire extract each day, we can just add the new transactions that occurred that day. (Then once a week you may want to do a full refresh just to be sure you have the most up to date data.)
But before configuring Incremental refresh we need to check following->
a) Does the data always gets inserted and never gets updated / Deleted ?
b) Does the data set have a unique key (A integer serial number which always increase or a date that always increase)?
If answer to both these questions in "Yes" then only we should configure Incremental Refresh or else we have to go for Full Refresh.
Reference:
https://community.tableau.com/thread/204061
