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From Akash Ashok <thehellma...@gmail.com>
Subject Re: How can HBase return the metadata to the client?
Date Sat, 08 Oct 2011 12:23:42 GMT
Hi,
The catalog regions .META. and -ROOT-  belong to the HBase cluster but are
not hosted by Master.

.META and -ROOT are hosted by region servers themselves but the state
information like, on which node the --ROOT- region resides is stored in
Zookeeper cluster under the znode "/hbase/root-region-server".

So essentially client contacts the zookeeper cluster and fetches the
information for /hbase/root-region-server, the address of the RegionServer
hosting -ROOT- region and then queries the ROOT region in turn which holds
the location of the .META. region and so on

Master on the other hand neither hosts any user nor the catalog tables.
Master mostly provides administrative functions like modification of the
tables, Region lifecycle management etc..

For more information you could refer to

http://ofps.oreilly.com/titles/9781449396107/architecture.html#archregionlifecycle

Cheers,
Akash A


On Sat, Oct 8, 2011 at 3:49 PM, yonghu <yongyong313@gmail.com> wrote:

> Hello,
>
> I read the blog
> http://www.larsgeorge.com/2009/10/hbase-architecture-101-storage.html and
> tried to understand the architecture of the HBase. There is one thing that
> makes me confusing. If I understand right, the client must connect the
> Zookeeper cluster to get the metadata of particular table information and
> then use this information to retrieve the table.
> My question is the node which hosts the  ".META. table" and "-ROOT- region"
> is the node which belongs to HBase cluster or Zookeeper cluster? If they
> belongs to the Zookeeper cluster, what is the functionality of the Master
> node in the HBase cluster, only assigning the work node when starting the
> HBase? In my point of view, the Master node will maintain the ".META.
> table"
> and "-ROOT- region" information.
>
> Thanks!
>
> Yong
>

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