Chen Liang created HDFS-11907:
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Summary: NameNodeResourceChecker should avoid calling
df.getAvailable too frequently
Key: HDFS-11907
URL: https://issues.apache.org/jira/browse/HDFS-11907
Project: Hadoop HDFS
Issue Type: Improvement
Reporter: Chen Liang
Assignee: Chen Liang
Currently, {{HealthMonitor#doHealthChecks}} invokes {{NameNode#monitorHealth}}
which ends up invoking {{NameNodeResourceChecker#isResourceAvailable}}, at the
frequency of once per second by default. And
NameNodeResourceChecker#isResourceAvailable invokes {{df.getAvailable();}}
every time it is called. Which can be a potentially very expensive operation.
Since available space information should rarely be changing dramatically at the
pace of per second. A cached value should be sufficient. i.e. only try to get
the updated value when the cached value is too old. otherwise simply return the
cached value. This way df.getAvailable() gets invoked less.
Thanks [~arpitagarwal] for the offline discussion.
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