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From lars hofhansl <la...@apache.org>
Subject Re: confused info about region-regionserver locality
Date Thu, 04 Apr 2013 18:04:45 GMT
Isn't this done via pipelining anyway?
So there's no notion of ordering with respect 1st, 2nd, and 3rd block, either all writes go
through the pipeline or none are.

When the write request returns to the client there will be a local copy, a copy on another
machine in the same, and a copy on a machine in a different rack, who cares about the ordering
inside the pipeline?

Seems it would also be inefficient to pipeline from the local rack to another another one
and then in the same pipeline back into the local rack (more load on the switch connecting
the racks with no benefit).

I'll double check.

-- Lars

 From: Jean-Marc Spaggiari <jean-marc@spaggiari.org>
To: user@hbase.apache.org 
Sent: Thursday, April 4, 2013 8:25 AM
Subject: Re: confused info about region-regionserver locality

I think you're right and documentation need to be updated.

The 3rd replica is written on a random node in the same rack as the
2nd replica. I will double check. Can you please open a JIRA so this
is updated?


2013/4/4 KIM JUN YOUNG <juneng603@me.com>:
> Hi All.
> There is confused understanding about region-regionser locality.
> from the current document ,
> http://hbase.apache.org/book/regions.arch.html
> 9.7.3. Region-RegionServer Locality
> Over time, Region-RegionServer locality is achieved via HDFS block replication. The HDFS
client does the following by default when choosing locations to write replicas:
> First replica is written to local node
> Second replica is written to another node in same rack
> Third replica is written to a node in another rack (if sufficient nodes)
> but, my understanding is different
> HDFS write blocks for replica
>         first, local node
>         second, another node in another rack
>         third, random another node in same rack
> need to be changed? or am I missing something?
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