Updated on 2022-09-15 GMT+08:00

Speculative Execution

Scenario

If a cluster has hundreds or thousands of nodes, the hardware or software fault of a node may prolong the execution time of the entire task (as most tasks are already completed, the system is still waiting for the task running on the faulty node). Speculative execution allows a task to be executed on multiple machines. You can disable speculative execution for small clusters.

Procedure

Navigation path for setting parameters:

On the All Configurations page of the Yarn service, enter a parameter name in the search box. For details, see Modifying Cluster Service Configuration Parameters.

Parameter

Description

Default Value

mapreduce.map.speculative

Sets whether to execute multiple instances of some map tasks concurrently. true indicates that speculative execution is enabled.

false

mapreduce.reduce.speculative

Sets whether to execute multiple instances of some reduce tasks concurrently. true indicates that speculative execution is enabled.

false