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From Jan Algermissen <jan.algermis...@nordsc.com>
Subject Hadoop/Cassandra for data transformation (rather than analysis)?
Date Sat, 10 Aug 2013 08:15:04 GMT
Hi,

I have a specific use case to address with Cassandra and I can't get my head around whether
using Hadoop on top creates any significant benefit or not.

Situation:

I have product data and each product 'contains' a number of articles (<100 / product),
representing individual colors/sizes etc.

My plan is to store each product in cassandra as a wide row, containing all the  articles
per product. I choose this design because sometimes I need to work with all the articles in
a product and sometimes I just need to pick one of them per product.

My understanding is that picking a certain 'row' from all the 'rows' in a wide row is nice
(because it works on a per-row basis) and that any other approach would require a scan over
essentially all the rows (not good).

So, after selecting one or  some or all of the 'rows' (articles) from every single wide row
(product) the input to my data processing is essentially a bunch articles.

The final output of the overall processing will be and export file (XML or CSV) containing
one line (or element) per article. There is no 'cross article' analysis going on, it is really
sort of one-in/on-out.

I am looking a Hadoop because I see MapReduce as a nice fit given the independence of the
per-article transformation into an output 'line'.

What I am worried about is whether Hadoop will actually give me a real benefit: While there
will be processing (mostly string operations) going on to vreate lines from articles, the
output still needs to be pulled over the wire to some place to create the single output file.


I wonder whether it would not work equally well to per-article pull the necessary data from
Cassandra and create the output file in a single process (in my case Java Web app). As I do
not have Billions of input records (but a max of 10 Milllion) the added benefit of scaling
out the per-line processing is probably not worth the additional setup and operations effort
of Hadoop. 

Any idea how I could make a judgement call here?

Another question: I read in a C* 1.1 related slidedeck that Hadoop output to CFS is only possible
with DSE and not with DSC - that with DSC the Hadoop output would be HDFS. Is that correct?
 For homogeneity, I would certainly want to store the output files in CFS, too.

Sorry, that this was a bit of a longer question/explanation.

Jan







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