Question

What is speculative execution?

Answer 1

If a node is executing a task slower then the master node. Then there is needs to redundantly execute one more instance of the same task on another node. So the task finishes first will be accepted and the other one likely to be killed. This process is known as “speculative execution.”

Answer 2

Speculative execution is one type of feature that is available in MapReduce, which provides the feature of allowing the launch of several tasks on different kinds of nodes. Sometimes, even some multiple copies were also made by the speculative execution. Generally, duplicate copies of the task will be created using this feature if one task takes a long time to process or get completed.

Answer 3

Hadoop run the process in commodity hardware, so it’s possible to fail the systems also has low memory. So if system failed, process also failed, it’s not recommendable.Speculative execution is a process performance optimization technique.Computation/logic distribute to the multiple systems and execute which system execute quickly. By default this value is true. Now even the system crashed, not a problem, framework choose logic from other systems.

Eg: logic distributed on A, B, C, D systems, completed within a time.

System A, System B, System C, System D systems executed 10 min, 8 mins, 9 mins 12 mins simultaneously. So consider system B and kill remaining system processes, framework take care to kill the other system process.