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From Joey Echeverria <j...@cloudera.com>
Subject Re: Hadoop--store a sequence file in distributed cache?
Date Fri, 12 Aug 2011 10:28:00 GMT
You can use any kind of format for files in the distributed cache, so
yes you can use sequence files. They should be faster to parse than
most text formats.


On Fri, Aug 12, 2011 at 4:56 AM, Sofia Georgiakaki
<geosofie_tuc@yahoo.com> wrote:
> Thank you for the reply!
> In each map(), I need to open-read-close these files (more than 2 in the general case,
and maybe up to 20 or more), in order to make some checks. Considering the huge amount of
data in the input, making all these file operations on HDFS will kill the performance!!! So
I think it would be better to store these files in distributed Cache, so that the whole process
would be more efficient -I guess this is the point of using Distributed Cache in the first
> My question is, if I can store sequence files in distributed Cache and handle them using
e.g. the SequenceFile.Reader class, or if I should only keep regular text files in distributed
Cache and handle them using the usual java API.
> Thank you very much
> Sofia
> PS: The files have small size, a few KB to few MB maximum.
> ________________________________
> From: Dino Kečo <dino.keco@gmail.com>
> To: common-user@hadoop.apache.org; Sofia Georgiakaki <geosofie_tuc@yahoo.com>
> Sent: Friday, August 12, 2011 11:30 AM
> Subject: Re: Hadoop--store a sequence file in distributed cache?
> Hi Sofia,
> I assume that output of first job is stored on HDFS. In that case I would
> directly read file from Mappers without using distributed cache. If you put
> file into distributed cache that would add one more copy operation into your
> process.
> Thanks,
> dino
> On Fri, Aug 12, 2011 at 9:53 AM, Sofia Georgiakaki
> <geosofie_tuc@yahoo.com>wrote:
>> Good morning,
>> I would like to store some files in the distributed cache, in order to be
>> opened and read from the mappers.
>> The files are produced by an other Job and are sequence files.
>> I am not sure if that format is proper for the distributed cache, as the
>> files in distr.cache are stored and read locally. Should I change the format
>> of the files in the previous Job and make them Text Files maybe and read
>> them from the Distr.Cache using tha simple Java API?
>> Or can I still handle them with the usual way we use sequence files, even
>> if they reside in the local directory? Performance is extremely important
>> for my project, so I don't know what the best solution would be.
>> Thank you in advance,
>> Sofia Georgiakaki

Joseph Echeverria
Cloudera, Inc.

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