[jira] Commented: (HADOOP-2144) Data node process consumes 180% cpu

["Raghu Angadi (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-2144?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12575479#action_12575479 ] 

Raghu Angadi commented on HADOOP-2144:
--------------------------------------

HADOOP-2758 has been committed. So DataNode cpu should be around 80 from 180 (more likely DataNode to client ratio goes to 4/10 from 9/10 for this test.).


> Data node process consumes 180% cpu 
> ------------------------------------
>
>                 Key: HADOOP-2144
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2144
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: Runping Qi
>            Assignee: Chris Douglas
>
> I did a test on DFS read throughput and found that the data node 
> process consumes up to 180% cpu when it is under heavi load. Here are the details:
> The cluster has 380+ machines, each with 3GB mem and 4 cpus and 4 disks.
> I copied a 10GB file to dfs from one machine with a data node running there.
> Based on the dfs block placement policy, that machine has one replica for each block of the file.
> then I run 4 of the following commands in parellel:
> hadoop dfs -cat thefile > /dev/null &
> Since all the blocks have a local replica, all the read requests went to the local data node.
> I observed that:
>     The data node process's cpu usage was around 180% for most of the time .
>     The clients's cpu usage was moderate (as it should be).
>     All the four disks were working concurrently with comparable read throughput.
>     The total read throughput was maxed at 90MB/Sec, about 60% of the expected total 
>     aggregated max read throughput of 4 disks (160MB/Sec). Thus disks were not a bottleneck
>     in this case.
> The data node's cpu usage seems unreasonably high.

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