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From Jean-Daniel Cryans <jdcry...@apache.org>
Subject Re: Regarding design of HDFS
Date Thu, 25 Aug 2011 16:45:41 GMT
In order to have an answer to that sort of question, you first must
prove that you did your own homework eg write down what you think the
answer is based on your observations and readings, then I'm sure
someone will be happy to help you.


On Thu, Aug 25, 2011 at 1:04 AM, Sesha Kumar <sesha911@gmail.com> wrote:
> Hi all,
> I am trying to get a good understanding of how Hadoop works, for my
> undergraduate project. I have the following questions/doubts :
> 1. Why does namenode store the blockmap (block to datanode mapping) in the
> main memory for all the files, even those that are not used?
> 2. Why cant namenode move out a part of the blockmap from main memory to a
> secondary storage device, when free space in main memory becomes scarce (
> due to large number of files) ?
> 3. Why cant the blockmap be constructed when a file is requested (by a
> client) and then be cached for later accesses?

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