FAQ
Hi,

(1) I declared a global variable in my hadoop mainClass which gets initialized in the 'run' function of this mainClass. When I try to access this global static variable from the MapperClass, it appears to be uninitialized.

Why is that? Is it because of the parallel execution of Hadoop functions ? but , isn't the 'run' function supposed to be the one to run first and prepare all the job configurations before the Maps even start?

(2) Fig 4.5 in http://developer.yahoo.com/hadoop/tutorial/module4.html shows the inputFormat to be the one running before the maps. My question is in which node? The JobTracker node?

Thank you,
Maha

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  • Li ping at Dec 31, 2010 at 2:13 am

    On Fri, Dec 31, 2010 at 9:28 AM, maha wrote:

    Hi,

    (1) I declared a global variable in my hadoop mainClass which gets
    initialized in the 'run' function of this mainClass. When I try to access
    this global static variable from the MapperClass, it appears to be
    uninitialized.

    Why is that? Is it because of the parallel execution of Hadoop
    functions ? but , isn't the 'run' function supposed to be the one to run
    first and prepare all the job configurations before the Maps even start?
    The Mapper will run on a remote machine, in other JVM, so the variable you
    set in Main class can not be shared with other VM.
    (2) Fig 4.5 in http://developer.yahoo.com/hadoop/tutorial/module4.html shows the inputFormat to be the one running before the maps. My question is
    in which node? The JobTracker node?
    I think it should run on JobTracker, The inputFormat will split the file
    and the map function will read the every splited file.
    Thank you,
    Maha



    --
    -----李平
  • Maha at Dec 31, 2010 at 4:59 am
    Very helpful :) thanks Ping.

    Maha
    On Dec 30, 2010, at 6:13 PM, li ping wrote:
    On Fri, Dec 31, 2010 at 9:28 AM, maha wrote:

    Hi,

    (1) I declared a global variable in my hadoop mainClass which gets
    initialized in the 'run' function of this mainClass. When I try to access
    this global static variable from the MapperClass, it appears to be
    uninitialized.

    Why is that? Is it because of the parallel execution of Hadoop
    functions ? but , isn't the 'run' function supposed to be the one to run
    first and prepare all the job configurations before the Maps even start?
    The Mapper will run on a remote machine, in other JVM, so the variable you
    set in Main class can not be shared with other VM.
    (2) Fig 4.5 in http://developer.yahoo.com/hadoop/tutorial/module4.html shows the inputFormat to be the one running before the maps. My question is
    in which node? The JobTracker node?
    I think it should run on JobTracker, The inputFormat will split the file
    and the map function will read the every splited file.
    Thank you,
    Maha



    --
    -----李平

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postedDec 31, '10 at 1:28a
activeDec 31, '10 at 4:59a
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