Dear Rakesh - Let me tell you, this forum is not for preparing for interview.
To answer your question in one line -- TDE (Tableau Data Extract) can't be created real-time.
Tableau can read data from 100 different sources and writes them into a columnar file that stores only unique values and pointers called TDE. While accessing the file, based on the Column fetched, only those columns gets loaded into memory. In memory processing is always fast, so any measure column in Tableau TDE files can be can be aggregated at lightning fast speed.
If your data is mission critical (Live Sensex, Fraud detection etc.) then you have to use Live connection only. Refreshing TDE will take time, based on the Number of rows and columns it will vary, but it will take atleast a minute to refresh, so Live TDE is practically not possible and not the Use Case Tableau wanted to solve through TDE. You can schedule a job that will full / incrementally refresh TDE based on an interval.
What should we do if we have millions of rows in live data, what is the approach we need to follow to increase the dashboard performance
what i am guessing is the RAM size or database capacity . or do we need to increase the server capacity. Any furhter information
can you provide on working with large live data sets.
As I have suggested in my previous post that you can have incremental refresh of your Extract. If your database is satisfying following three condition then you can implement incremental refresh, that won't take much time.
Condition 1: You need to have a database Key (Preferably an integer which will ever increasing or a time which will never decrease). You can use this as key to implement incremental refresh of Tableau
Condition 2: Your data should never get deleted / updated from backend. New data should always get added
Condition 3: Your data relationship shouldn't get changed.
If the above conditions met then you can implement incremental refresh and believe me, incremental refresh is really fast.
Your source query should be tuned. Btw, you always have Live option if nothing works.
Hope you get your answer.