Tianyin Xu created YARN-4499:
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Summary: Bad config values of "scheduler.maximum-allocation-vcores"
Key: YARN-4499
URL: https://issues.apache.org/jira/browse/YARN-4499
Project: Hadoop YARN
Issue Type: Bug
Components: scheduler
Affects Versions: 2.6.2, 2.7.1
Reporter: Tianyin Xu
Currently, the default value of {{yarn.scheduler.maximum-allocation-vcores}} is
{{4}}, according to {{YarnConfiguration.java}}
{code}
public static final String RM_SCHEDULER_MAXIMUM_ALLOCATION_VCORES =
YARN_PREFIX + "scheduler.maximum-allocation-vcores";
public static final int DEFAULT_RM_SCHEDULER_MAXIMUM_ALLOCATION_VCORES = 4;
{code}
However, according to
[yarn-default.xml|https://hadoop.apache.org/docs/r2.7.1/hadoop-yarn/hadoop-yarn-common/yarn-default.xml],
this value should be {{32}}.
Yes, this seems to be a doc error, but I feel that the default value should be
the same as {{yarn.nodemanager.resource.cpu-vcores}} ---if we have {{8}} cores
for scheduling, there's few reason we only allow the maximum of {{4}}...
The Cloudera's article on [Tuning the Cluster for MapReduce v2 (YARN)
|http://www.cloudera.com/content/www/en-us/documentation/enterprise/5-3-x/topics/cdh_ig_yarn_tuning.html]
also suggests that "the maximum value (of
{{yarn.nodemanager.resource.cpu-vcores}}) is usually equal to
{{yarn.nodemanager.resource.cpu-vcores}}..."
The doc error is pretty bad. A simple search on the Internet shows some ppl are
confused by this error, for example,
https://community.cloudera.com/t5/Cloudera-Manager-Installation/yarn-nodemanager-resource-cpu-vcores-and-yarn-scheduler-maximum/td-p/31098
(seriously, I think we should have an automatic default which is equal to the
number of cores on the machine...)
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