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From Marko Dinic <marko.di...@nissatech.com>
Subject Re: Large number of small files
Date Fri, 24 Apr 2015 09:47:59 GMT

Thank you very much for the clarification. Can you please explain how 
would I be able to add new files to the parquet file? Since the files 
today won't be the same as the files that were used yesterday, since 
new files are added since yesterday?


On Fri 24 Apr 2015 11:33:03 AM CEST, Chandra Mohan, Ananda Vel Murugan 
> Marko,
> Parquet file would be created once when you load the data. You don’t
> have to store your small files in HDFS just for the reason of
> subseting the data by time range. You can store data and metadata in
> same Parquet file. As already pointed out, parquet files work well
> other tools in Hadoop ecosystem. Apart from performance of your map
> reduce jobs, other aspect is storage efficiency. Serialization formats
> like Avro and Parquet provide better compression and hence data
> occupies less space.
> Regards,
> Anand
> *From:*Alexander Alten-Lorenz [mailto:wget.null@gmail.com]
> *Sent:* Friday, April 24, 2015 2:49 PM
> *To:* user@hadoop.apache.org
> *Subject:* Re: Large number of small files
> Marko,
> Cassandra is an noSQL DB like HBase for Hadoop is. Pro and cons
> wouldn't be discussed here.
> Parquet is an columnar based storage format. It is - high level - a
> bit like a NoSQL DB, but on the storage level. it allows users to
> "query" the data with MR, Pig or similar tools. Additionally, Parquet
> works perfectly with Hive and Cloudera Impala as well as Apache Dremel.
> https://parquet.incubator.apache.org/documentation/latest/
> http://www.cloudera.com/content/cloudera/en/documentation/cloudera-impala/v2-0-x/topics/impala_parquet.html
> https://zoomdata.zendesk.com/hc/en-us/articles/200865073-Loading-My-CSV-Data-into-Impala-as-a-Parquet-Table
> --
> Alexander Alten-Lorenz
> m: wget.null@gmail.com <mailto:wget.null@gmail.com>
> b: mapredit.blogspot.com <http://mapredit.blogspot.com>
>     On Apr 24, 2015, at 11:10 AM, Marko Dinic
>     <marko.dinic@nissatech.com <mailto:marko.dinic@nissatech.com>> wrote:
>     Anand,
>     Thank you for your answer, but wouldn't that mean that I would
>     have to serialize the files each time I need to run the job? And I
>     would still need to save the original files, so the NameNode still
>     needs to take care of them?
>     Please correct me if I'm missing something, I'm not very
>     experienced with Hadoop.
>     What do you think about using Cassandra?
>     Thanks
>     On Fri 24 Apr 2015 11:03:19 AM CEST, Chandra Mohan, Ananda Vel
>     Murugan wrote:
>     Apart from databases like Cassandra, you may check serialization
>     formats like Avro or Parquet
>     Regards,
>     Anand
>     -----Original Message-----
>     From: Marko Dinic [mailto:marko.dinic@nissatech.com]
>     Sent: Friday, April 24, 2015 2:23 PM
>     To: user@hadoop.apache.org <mailto:user@hadoop.apache.org>
>     Subject: Large number of small files
>     Hello,
>     I'm not sure if this is the place to ask this question, but I'm
>     still hopping for an answer/advice.
>     Large number of small files are uploaded, about 8KB. I am aware
>     that this is not something that you're hopping for when working
>     with Hadoop.
>     I was thinking about using HAR files and combined input, or
>     sequence files. The problem is, files are timestamped, and I need
>     different subset in different time, for example - one job needs to
>     run on files that are uploaded during last 3 months, while next
>     job might consider last 6 months. Naturally, as time passes
>     different subset of files is needed.
>     This means that I would need to make a sequence file (or a HAR)
>     each time I run a job, to have smaller number of mappers. On the
>     other hand, I need the original files so I could subset them. This
>     means that DataNode is at constant pressure, saving all of this in
>     its memory.
>     How can I solve this problem?
>     I was also considering using Cassandra, or something like that,
>     and to save the file content inside of it, instead of saving it to
>     files on HDFS. FIle content is actually some measurement, that is,
>     a vector of numbers, with some metadata.
>     Thanks

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