[jira] [Created] (HADOOP-17461) Add thread-level IOStatistics Context

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[jira] [Created] (HADOOP-17461) Add thread-level IOStatistics Context

Steve Loughran (Jira)
Steve Loughran created HADOOP-17461:

             Summary: Add thread-level IOStatistics Context
                 Key: HADOOP-17461
                 URL: https://issues.apache.org/jira/browse/HADOOP-17461
             Project: Hadoop Common
          Issue Type: Sub-task
          Components: fs, fs/azure, fs/s3
    Affects Versions: 3.3.1
            Reporter: Steve Loughran

For effective reporting of the iostatistics of individual worker threads, we need a thread-level context which IO components update.

* this contact needs to be passed in two background thread forming work on behalf of a task.
* IO Components (streams, iterators, filesystems) need to update this context statistics as they perform work
* Without double counting anything.

I imagine a ThreadLocal IOStatisticContext which will be updated in the FileSystem API Calls. This context MUST be passed into the background threads used by a task, so that IO is correctly aggregated.

I don't want streams, listIterators &c to do the updating as there is more risk of double counting. However, we need to see their statistics if we want to know things like "bytes discarded in backwards seeks". And I don't want to be updating a shared context object on every read() call.
If all we want is store IO (HEAD, GET, DELETE, list performance etc) then the FS is sufficient.
If we do want the stream-specific detail, then I propose
* caching the context in the constructor
* updating it only in close() or unbuffer() (as we do from S3AInputStream to S3AInstrumenation)
* excluding those we know the FS already collects.

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