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From Gy├Ârgy Balogh <bogyo...@gmail.com>
Subject Poor performance on word count test on a 10 node cluster.
Date Mon, 16 May 2011 07:15:26 GMT

I have a 10 node cluster (IBM blade servers, 48GB RAM, 2x500GB Disk, 16 HT

I've uploaded 10 files to HDFS. Each file is 10GB. I used the streaming jar
with 'wc -l' as mapper and 'cat' as reducer.

I use 64MB block size and the default replication (3).

The wc on the 100 GB took about 220 seconds which translates to about 3.5
Gbit/sec processing speed. One disk can do sequential read with 1Gbit/sec so
i would expect someting around 20 GBit/sec (minus some overhead), and I'm
getting only 3.5.

Is my expectaion valid?

I checked the jobtracked and it seems all nodes are working, each reading
the right blocks. I have not played with the number of mapper and reducers
yet. It seems the number of mappers is the same as the number of blocks and
the number of reducers is 20 (there are 20 disks). This looks ok for me.

Thank you,

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