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From Bjorn Jonsson <bjorn...@gmail.com>
Subject Re: Distributed cache: how big is too big?
Date Tue, 09 Apr 2013 23:07:12 GMT
I think the correct question is why would you use distributed cache for a
large file that is read during map/reduce instead of plain hdfs? It does
not sound wise to shuffle GB of data onto all nodes on each job submission
and then just remove it when the job is done. I would think about picking
another "data strategy" and just use hdfs for the file. Its no problem to
make sure the file is available on every node.

Anyway...maybe someone with more knowledge on this will chip in :)


On Tue, Apr 9, 2013 at 7:56 AM, Jay Vyas <jayunit100@gmail.com> wrote:

> Hmmm.. maybe im missing something.. but (@bjorn) Why would you use hdfs as
> a replacement for the distributed cache?
>
> After all - the distributed cache is just a file with replication over the
> whole cluster, which isn't in hdfs.  Cant you Just make the cache size big
> and store the file there?
>
> What advantage is hdfs distribution of the file over all nodes  ?
>
> On Apr 9, 2013, at 6:49 AM, Bjorn Jonsson <bjornjon@gmail.com> wrote:
>
> Put it once on hdfs with a replication factor equal to the number of DN.
> No startup latency on job submission or max size and access it from
> anywhere with fs since it sticks around untill you replace it? Just a
> thought.
> On Apr 8, 2013 9:59 PM, "John Meza" <j_mezazap@hotmail.com> wrote:
>
>> I am researching a Hadoop solution for an existing application that
>> requires a directory structure full of data for processing.
>>
>> To make the Hadoop solution work I need to deploy the data directory to
>> each DN when the job is executed.
>> I know this isn't new and commonly done with a Distributed Cache.
>>
>> *Based on experience what are the common file sizes deployed in a
>> Distributed Cache?*
>> I know smaller is better, but how big is too big? the larger cache
>> deployed I have read there will be startup latency. I also assume there are
>> other factors that play into this.
>>
>> I know that->Default local.cache.size=10Gb
>>
>> -Range of desirable sizes for Distributed Cache= 10Kb - 1Gb??
>> -Distributed Cache is normally not used if larger than =____?
>>
>> *Another Option:* Put the data directories on each DN and provide
>> location to TaskTracker?
>>
>> thanks
>> John
>>
>>

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