This is detail! How often Google updates and what happens to the data in the index during the not-insignificant time that an update is taking place

Google Dance

The Google search engine pulls its results from more than 10,000 servers which are which are simple Linux PCs that are used by Google for reasons of cost. Naturally, an index update cannot be proceeded on all those servers at the same time. One server after the other has to be updated with the new index.