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From "Siddharth Seth (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MAPREDUCE-2349) speed up list[located]status calls from input formats
Date Wed, 19 Mar 2014 23:15:48 GMT

     [ https://issues.apache.org/jira/browse/MAPREDUCE-2349?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Siddharth Seth updated MAPREDUCE-2349:
--------------------------------------

    Attachment: MAPREDUCE-2349.5.txt

Thanks for the review. Updated patch attached.

bq. Add the configs to mapred-default.xml as documentation?
Done.
bq. LIST_STATUS_NUM_THREADS_DEFAULT -> DEFAULT_LIST_STATUS_NUM_THREADS
Done.
bq. oldListStatus() -> singleThreadedListStatus()
Done
bq. Can you add a bit of javadoc to all the new classes and methods in LocatedFileStatusFetcher?
Also to the main LocatedFileStatusFetcher class itself.
Done
bq. Synchronization needed for ProcessInitialInputPathResult.addError()?
Not required. It's local to the specific instance.
bq. Can you group the callable, result and call-back for each type of operation together in
two classes?
Moved the Result into the callable. The CallbackHandler is non static - so moving that requires
a fair amount of change, and additional parameters. Have left that as is.
bq. The 'result' variable doesn't need to be a class field of ProcessInputDirCallable. Similarly
the one in ProcessInitialInputPathCallable.
Made this local to the method.

Also fixed a typo in one of the log messages

> speed up list[located]status calls from input formats
> -----------------------------------------------------
>
>                 Key: MAPREDUCE-2349
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2349
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: task
>            Reporter: Joydeep Sen Sarma
>            Assignee: Siddharth Seth
>         Attachments: MAPREDUCE-2349.1.wip.txt, MAPREDUCE-2349.2.txt, MAPREDUCE-2349.3.txt,
MAPREDUCE-2349.4.txt, MAPREDUCE-2349.5.txt
>
>
> when a job has many input paths - listStatus - or the improved listLocatedStatus - calls
(invoked from the getSplits() method) can take a long time. Most of the time is spent waiting
for the previous call to complete and then dispatching the next call. 
> This can be greatly speeded up by dispatching multiple calls at once (via executors).
If the same filesystem client is used - then the calls are much better pipelined (since calls
are serialized) and don't impose extra burden on the namenode while at the same time greatly
reducing the latency to the client. In a simple test on non-peak hours, this resulted in the
getSplits() time reducing from about 3s to about 0.5s.



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