在YARN中，如何控制和监控map/reduce的并发数

配置建议：

1.
    In MR1, the mapred.tasktracker.map.tasks.maximum and mapred.tasktracker.reduce.tasks.maximum properties dictated how many map and reduce slots each TaskTracker had.

    These properties no longer exist in YARN. Instead, YARN uses yarn.nodemanager.resource.memory-mb and yarn.nodemanager.resource.cpu-vcores, which control the amount of memory and CPU on each node, both available to both maps and reduces

    Essentially:
YARN has no TaskTrackers, but just generic NodeManagers. Hence, there's no more Map slots and Reduce slots separation. Everything depends on the amount of memory in use/demanded

2.

Using the web UI you can get lot of monitoring/admin kind of info:

NameNode - http://:50070/ 
Resource Manager - http://:8088/

其他配置参考：

1. There is a good guide on YARN configuration from Hortonworks
2. You may analyze your job in Job History server. It usually may be found on port 19888. Ambari andGanglia are also very good for cluster utilization measurement.