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NodeGroup Performance Issues

Babak Behzad explains potential Hadoop NodeGroup performance bottlenecks:

As can be seen in the logs, the localityWaitFactor value is 1, but the delay that this code causes grows linearly with the number of required containers. Since our DFSIO-large benchmark creates 1,024 files, each 1 GB in size, it requests 1,024 YARN containers. Therefore, the code has to miss at least 1,024 scheduling opportunities until it schedules containers on this (wrongly assumed) OFF_SWITCH node.

But why is this delay enforced? This idea falls into a big area of scheduling research. The Delay Scheduling algorithm was introduced by Matei Zaharia’s EuroSys ’10 paper titled “Delay Scheduling: A Simple Technique for Achieving Locality and Fairness in Cluster Scheduling”.

That post is a bit deeper than my Hadoop administration comfort level, but if you’re given the task of performance tuning a cluster, this might be one place to look.