The Neo4j database's reactive drivers were introduced in version 4.0, enabling a gate between the client and server to control the flow of data and adjust it accordingly. This allows for efficient fetching of large amounts of data without overloading the client or server. The reactive drivers use operators such as bufferCount() and takeUntil(), which enable the client to define the size of results they can accept each time, and force the notifier to emit a value when the desired number of unique nodes is reached. This technique can be used for any data processing that requires size limitations on the client side.