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From MONTMORY Alain <alain.montm...@thalesgroup.com>
Subject How to count records in FileInputFormat (MapFile, SequenceFile ?)
Date Thu, 08 Sep 2011 08:58:07 GMT
Hi everyBody,

In my application the treatment of the whole dataset (that we called CycleWorkflow) may have
a duration of several weeks and we want (mandatory) to split the CycleWorkflow into multiple
The actual system use a traditionnal RDBMS approach and use SQL OFFSET LIMIT to split the
dataset (potentially 80 billions rows in  one table) into smaller datasets. We are actually
(re)designing the application using Hadoop/Cascading/HDFS and we try to found a feature to
split MapFile in input (with 80 billions key) according to the number of record.
CycleDataset = 10000 <key,value> record
Split1 = 0 <key,value>  to 1000<key,value>    = Dataset for DayWorkflow1
Split2 = 2000 <key,value>  to 3000<key,value>   = Dataset for DayWorkflow2
Split3 = 3000 <key,value>  to 4000<key,value>   = Dataset for DayWorkflow3
We expect to use MapFile  (is it a good choice? or is there another existing file format?
(HFile?) more suitable for this usage...).
The progress  monitoring (bargraph in a GUI) of DayWorkflowX are currently done with the number
of record already processed by this workflow.

In MapFile class i don't find API to count record efficiently.. am I missing something ? (probably
Which solution do you suggest to split Input Dataset according to the number of <key,value>
record ?

Thank you for your response..


(we are using Hadoop 0.20.xx version)


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