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From Juhani Connolly <juhani_conno...@cyberagent.co.jp>
Subject Re: 0.92 and Read/writes not scaling
Date Thu, 05 Apr 2012 01:45:26 GMT
another quick update on stuff:

since moving back to hdfs 0.20.2 (with hbase still at 0.92), we found 
that while we made significant gains in throughput, that most of our 
regionservers IPC threads were stuck somewhere in HWal.append(out of 50, 
42 were in append, of which 20 were in sync), limiting throughput 
despite significant free hardware resources.

Because the WAL writes of a single  RS all go sequentially to one HDFS 
file, we assumed that we could improve throughput by separating writes 
to more WAL files and more HDs. To do this we ran multiple region 
servers on each node.

The scaling  wasn't linear(we were in no way increasing hardware, just 
the number of regionservers), but we are now getting significantly more 
throughput.
I would personally not say that this is a great approach to have to 
take, it would generally be better to build more smaller servers which 
will thus not limit themselves by trying to put a lot of data per server 
through a single WAL file.

Of course there may be another solution to this that I'm not aware of? 
If so I'd love to hear it.

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