By virtualization I meant also not loading entire dataset to memory, but being able to work only on a constrained view of the data. For example, database has 1TB dataset, I only view 100 MB, further columns/sections are loaded when I scroll.

It is virtual in the sense that it does not realize the entire dataset in the JS side of the WebAssembly bridge - this is a performance optimization but entirely in-memory. While you can run the engine in node.js and use it to efficiently stream updates to a symmetric engine in the browser, we do not currently implement server-virtualized views.

Though, we have quite alot of experience doing this in the past - and the design of Perspective is very much a reaction to what we learned, at lesat in regards to the typical financial dataset which is much smaller than 1TB.

Is there a way to drill down a node dynamically, by clicking on row header during pivoting, and then see its children?

Not through the UI yet, only in the engine API - but the pivoting itself is quite fast, so should still be suitable for drilling down "on the fly" so to stpeak