[badave]

When they come out with new algorithms for searching, they are completely replacing their old engine, correct? Are they rewriting the core? Or is this more like v1 was PageRank, v2 was Caffeine, and Hummingbird is v3? Is a lot of the code is just being refactored or is everything getting rewritten?

[phy6]

It's more likely that they stand up several current versions in parallel, and progressively route more traffic to the new algorithms/services. At least that's what I'd do, if I had no technical, infrastructure or monetary budget.

[simcop2387]

I'd be surprised if that's not how they do it. Less for budgetary reasons and more for testing, doing it this way would let them see if they get the results they are after in aggregate for more useful queries