Comment by pradn

Graphs are inherently "chatty" because there are more shapes in which you could store them. The same goes for querying. Similar to "degrees of freedom".

Even storing a graph in memory, you're going to have load a lot more cache lines to traverse/query its structure. For remote graphs, this translates into more network calls.

The smart thing Netflix did here is finding the minimal abstraction that supports their online querying needs. Turns out that they need a few things above a bare KV store:

1) Idempotency keys allow multiple reads/writes without reordering issues. You can use them to do request hedging, which greatly helps w/ tail latency, at the cost of higher resource usage.

2) KV, with the value being a map. A little more structure, which can use the backing store's native structure.

3) Passing client/server parameters back and forth in a handshake. This allows clear request policy propagation, so the whole path behaves the way the client op wants it to.

4) Filtering/selection - to reduce the set of items returned, on the server side. So the network + client don't have to bear the extra burden.

The summary is: "minimal viable structure", "maximal chances to hedge requests / reduce data movement".