1. A method, performed by one or more computing devices, for snapshot consistency, the method comprising: storing, in persistent storage, graph data that includes a first graph that is stored in a first format and that comprises a first plurality of nodes and a first plurality of edges between the first plurality of nodes; reading, into volatile memory, a first instance of the first graph, wherein reading comprises processing the first graph to generate the first instance that is stored in a second format that is different than the first format; wherein the first instance represents a read-only snapshot of the first graph at a particular point in time; while storing the first instance in the volatile memory, receiving a first set of updates to the first graph, wherein the first instance is not modified by the first set of updates; wherein the first set of updates includes one or more of: an addition of a first node to the first plurality of nodes, a deletion of a second node from the first plurality of nodes, an addition of a first edge to the first plurality of edges, or a deletion of a second edge from the first plurality of edges; in response to receiving the first set of updates, storing the first set of updates in the persistent storage; after storing the first set of updates in the persistent storage and without updating the first instance, performing one or more first graph analysis operations on the first instance representing the read-only snapshot that has not been modified based on any update in the first set of updates.