Task

This is the most granular unit of task execution in Storm. Each task is an instance of a spout or bolt. When defining a Storm topology, you can specify the number of tasks for each spout and bolt. Once defined, the number of tasks cannot be changed for a component at runtime. Each task can be executed alone or with another task of the same type, or another instance of the same spout or bolt.

The following diagram depicts the relationship between a worker process, executors, and tasks. In the following diagram, there are two executors for each component, with each hosting a different number of tasks.

Also, as you can see, there are two executors and eight tasks defined for one component (each executor is hosting four tasks). If you are not getting enough performance out of this configuration, you can easily change the number of executors for the component to four or eight to increase performance and the tasks will be uniformly distributed between all executors of that component. The following diagrams show the relationship between executor, task, and worker: