Final answer:
A Task instance in Hadoop is a single unit of work that forms part of a larger job, which is executed by TaskTracker daemons on nodes within a Hadoop cluster. It can be either a Map task or a Reduce task, running in its own JVM process.
Step-by-step explanation:
In the context of Hadoop, a Task instance refers to a single unit of work that Hadoop can assign and execute as a part of a larger job typically within a Hadoop cluster. When a job is submitted to Hadoop, the job is divided into smaller pieces, each of which is a Task instance. These Task instances are executed by TaskTracker daemons that run on the cluster's nodes (DataNodes). Specifically, there are two types of task instances in Hadoop:
- Map tasks: These tasks deal with processing one block of data and achieve the mapping part of the MapReduce paradigm. A Map task is responsible for reading data from HDFS, processing it, and producing intermediate, serialized data.
- Reduce tasks: Once the Map tasks have finished processing the data, the Reduce tasks aggregate the results to derive a final output. These tasks work on the outputs of the Map tasks, combining the intermediate data into a smaller, often sorted set that represents the final result.
Every Task instance runs in its own JVM process to ensure that a single failing Task instance doesn't affect the other running tasks. This architecture aids in improving the robustness and scalability of the Hadoop cluster.