This will increase performance since the data is in extract mode.
On Thursday, October 29, 2015, CHEN Junxian <
Hi Benjamin, there is no clear cut answer to this I'm afraid, it is very dependent on data volume and complexity, the speed of your data base and the power of your Tableau Server. The only answer is to test it and see!
What Peter said... I can say from my own deployment that using an extract (built from Custom SQL using lots of joins with multiple subqueries on an MS Access database) is 10 to 100+x faster than the live custom SQL.
As others have stated above, using an EXTRACT (Built from a Custom SQL Statement) will be faster than using a Live Connection (The exception to this being highly indexed database systems [Others have reported Live Connections to Redshift are faster than Extracts - Or the they see no visible impact]).
As far as the EXTRACT process, (From personal experience) using a DB VIEW was faster than using CUSTOM SQL. Though I am not sure why....I am not a DB Admin LOL.