By default, tasks are grouped by node. However, task execution in elasticsearch can be quite complex and an individual task that runs on a coordinating node can have many subtasks running on other nodes in the cluster. This commit makes it possible to list task grouped by common parents instead of by node. When this option is enabled all subtask are grouped under the coordinating node task that started all subtasks in the group. To group tasks by common parents, use the following syntax:
GET /tasks?group_by=parents
Igor Motov