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Re: External db
Hi Kishore,
   you are comparing apples and oranges. HDFS is a file system (you read
and write files to it). The NoSQL datastores are more like
a database. You can query and depending on the type of NoSQL database
the querying can be more or less sophisticated e.g. "Give
me a document that contains a sub-document xyz".  You could write a
MapReduce program to do the querying (that is how Hive works
for example) but HDFS itself just stores files. Some NoSQL datastores
like HBase and Accumulo use HDFS as the underlying
file system just as a MySQL database might be using a WIndows NTFS file
system or Linux ext4 system to store the data.
Chris
On 12/15/2013 8:21 AM, Kishore wrote:
> Hi experts,
>
> What exactly needed the nosql database like Cassandra, hbase and mongodb when we have hdfs, ofcourse
> It supports oltp, are we storing the results from hdfs and reanalysing in nosql?
>
> Sent from my iPhone.
>