Speculative execution should be allowed for reducers only
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Key: HADOOP-2131
URL: https://issues.apache.org/jira/browse/HADOOP-2131
Project: Hadoop
Issue Type: Improvement
Components: mapred
Environment: Hadoop job, map fetches data from external systems
Reporter: Srikanth Kakani
Priority: Critical
Fix For: 0.15.0
Consider hadoop jobs where maps fetch data from external systems, and emit the
data. The reducers in this are identity reducers. The data processed by these
jobs is huge. There could be slow nodes in this cluster and some of the
reducers run twice as slow as their counterparts. This could result in a long
tail. Speculative execution would help greatly in such cases. However given the
current hadoop, we have to select speculative execution for both maps and
reducers. In this case hurting the map performance as they are fetching data
from external systems thereby overloading the external systems.
Speculative execution only on reducers would be a great way to solve this
problem.
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