[jira] [Created] (HADOOP-13695) S3A to use a thread pool for async path operations

["Steve Loughran (JIRA)" <ji...@apache.org>]

Steve Loughran created HADOOP-13695:
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             Summary: S3A to use a thread pool for async path operations
                 Key: HADOOP-13695
                 URL: https://issues.apache.org/jira/browse/HADOOP-13695
             Project: Hadoop Common
          Issue Type: Sub-task
          Components: fs/s3
    Affects Versions: 2.8.0
            Reporter: Steve Loughran


S3A path operations are often slow due to directory scanning, mock directory create/delete, etc. Many of these can be done asynchronously

* because deletion is eventually consistent, deleting parent dirs after an operation has returned doesn't alter the behaviour, except in the special case of : operation failure.
* scanning for paths/parents of a file in the create operation only needs to complete before the close() operation instantiates the object, no need to block create().
* parallelized COPY calls would permit asynchronous rename.

We could either use the thread pool used for block writes, or somehow isolate low cost path ops (GET, DELETE) from the more expensive calls (COPY, PUT) so that a thread doing basic IO doesn't block for the duration of the long op. Maybe also use {{Semaphore.tryAcquire()}} and only start async work if there actually is an idle thread, doing it synchronously if not. Maybe it depends on the operation. path query/cleanup before/after a write is something which could be scheduled as just more futures to schedule in the block write.



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