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From Jean-Marc Spaggiari <jean-m...@spaggiari.org>
Subject Re: confused info about region-regionserver locality
Date Thu, 04 Apr 2013 18:24:43 GMT
>Isn't this done via pipelining anyway?
Yes, it's the way it's done.

>So there's no notion of ordering with respect 1st, 2nd, and 3rd block, either all writes
go through the pipeline or none are.
Still correct.

> 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?
Not necessary. There might not be any additional copy on a different
machine on the same rack. BUT.. As you said, who cares ;) As long as
we have the local copy and some replicas.

I have updated the documentation already. I will open the JIRA and
submit. I have also added subsequent replicas in case replication
factor is > 3.

JM

2013/4/4 lars hofhansl <larsh@apache.org>:
> 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


>
> Hi,
>
> 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?
>
> JM
>
> 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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