mehakmeet opened a new pull request, #4639:
URL: https://github.com/apache/hadoop/pull/4639

   This adds a thread-level collector of IOStatistics, IOStatisticsContext,
   which can be:
   * Retrieved for a thread and cached for access from other
     threads.
   * reset() to record new statistics.
   * Queried for live statistics through the
     IOStatisticsSource.getIOStatistics() method.
   * Queries for a statistics aggregator for use in instrumented
     classes.
   * Asked to create a serializable copy in snapshot()
   
   The goal is to make it possible for applications with multiple
   threads performing different work items simultaneously
   to be able to collect statistics on the individual threads,
   and so generate aggregate reports on the total work performed
   for a specific job, query or similar unit of work.
   
   Some changes in IOStatistics-gathering classes are needed for 
   this feature
   * Caching the active context's aggregator in the object's
     constructor
   * Updating it in close()
   
   Slightly more work is needed in multithreaded code,
   such as the S3A committers, which collect statistics across
   all threads used in task and job commit operations.
   
   Currently the IOStatisticsContext-aware classes are:
   * The S3A input stream, output stream and list iterators.
   * RawLocalFileSystem's input and output streams.
   * The S3A committers.
   * The TaskPool class in hadoop-common, which propagates
     the active context into scheduled worker threads.
   
   Collection of statistics in the IOStatisticsContext
   is disabled process-wide by default until the feature 
   is considered stable.
   
   To enable the collection, set the option
   fs.thread.level.iostatistics.enabled
   to "true" in core-site.xml;
        
   Contributed by Mehakmeet Singh and Steve Loughran
   
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   ### Description of PR
   
   
   ### How was this patch tested?
   Region: `ap-south-1`
   All tests ran successfully.
   
   ### For code changes:
   
   - [X] Does the title or this PR starts with the corresponding JIRA issue id 
(e.g. 'HADOOP-17799. Your PR title ...')?
   - [X] Object storage: have the integration tests been executed and the 
endpoint declared according to the connector-specific documentation?
   - [X] If adding new dependencies to the code, are these dependencies 
licensed in a way that is compatible for inclusion under [ASF 
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