Hello Ashwath,

First Paralle queries are simply the allowance of more than one connection from the Tableau Server to a specific data source at a time. These limits can be set and modified as outlined here: Configuring Parallel Queries in Tableau Desktop | Tableau Software

I will do my best to provide as many resources about the above:

For data engine vectorization I found:

What is "Data Engine Vectorization"?

For Parallel aggregation:

What is "Parallel aggregation"?

A little more information on external query caching can be found here:

https://tableaulove.com/tableau-server-caching-exactly-refresh-less-often-mean/

Finally some additinoal information query fusion can be found here:

Tableau Query Fusion, you had me at hello. | Tableau Love

Hope these resources help!

Cheers,

Byrne, Patrick