Hands-On Reactive Programming in Spring 5

上QQ阅读APP看书，第一时间看更新

Bounded drop queue

Alternatively, to avoid a memory overflow, we may employ a queue that may ignore incoming messages if it is full. The following marble diagram depicts a queue that has a size of 2 elements and is characterized by dropping elements on overflow (Diagram 3.5):

Diagram 3.5. Example of Drop Queue with a capacity of two items

In general, this technique respects the resources' limitations and makes it possible to configure the capacity of the queue based on the resources' capacities. In turn, embracing this kind of queue is a common practice when the importance of the message is low. An example of a business case may be a stream of dataset-changed events. In turn, each event triggers some statistical recalculation which uses the entire dataset aggregation and takes a significant amount of time in comparison with the incoming events quantity. In that case, the only important thing is the fact that the data set changed; it is not vital to known which data has been affected.

Th e preceding mentioned example considers the simplest strategy for dropping the newest element. In general, there are a few strategies for choosing the element to drop. For example, dropping by priority, dropping the oldest, and so on.