How to show 1 million records in webgrid at mvc4?

You don't want to display all record at once. It would take forever and the browser might run out of memory... You'll have to use paging and display say 2000 pages of 500 records.

It does not make much sense to display more than a few thousand records at once in client/server architecture as there is too much data transfert.

Well, there might be a solution... use a grid control that supports virtualization and only load records around displayed data. For that, you will typically need client-side control like some kind of jQuery grid...

If you want to allows sorting, then you would also need indexes at the database level for such large data so that you can get only the required data in a reasonable amount of time.

Very large grid a generally considered as a bad design. At one million record it is very hard to navigate at a specific location as scrollabar are imprecise (it can move thousand of record for each pixel of movement) or very slow if you move one page at a time (assuming 50 visible records, it take 20 key press per thousand records)