Let’s go through the diagram piece by piece. * (A)—All new data is sent to both the batch layer and the speed layer. In the batch layer, new data is appended to the master dataset. In the speed layer, the new data is consumed to do incremental updates of the realtime views. * (B)—The master dataset is an immutable, append-only set of data. The master dataset only contains the rawest information that is not derived from any other information you have. * (C)—The batch layer precomputes query functions from scratch. The results of the batch layer are called batch views. The batch layer runs in a while(true) loop and continuously recomputes the batch views from scratch. The strength of the batch layer is its ability to compute arbitrary functions on arbitrary data. This gives it the power to support any application. * (D)—The serving layer indexes the batch views produced by the batch layer and makes it possible to get particular values out of a batch view very quickly. The serving layer is a scalable database that swaps in new batch views as they’re made available. Because of the latency of the batch layer, the results available from the serving layer are always out of date by a few hours. * (E)—The speed layer compensates for the high latency of updates to the serving layer. It uses fast incremental algorithms and read/write databases to produce realtime views that are always up to date. The speed layer only deals with recent data, because any data older than that has been absorbed into the batch layer and accounted for in the serving layer. The speed layer is significantly more complex than the batch and serving layers, but that complexity is compensated by the fact that the realtime views can be continuously discarded as data makes its way through the batch and serving layers. So, the potential negative impact of that complexity is greatly limited. * (F)—Queries are resolved by getting results from both the batch and realtime views and merging them together.