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From "Eric Caspole (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-2243) DataXceiver per accept seems to be a bottleneck in HBase/YCSB test
Date Tue, 23 Aug 2011 15:43:29 GMT

     [ https://issues.apache.org/jira/browse/HDFS-2243?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Eric Caspole updated HDFS-2243:
-------------------------------

    Attachment: HDFS-2234-branch-0.20-append.patch

Here is a thread pool patch based on branch-0.20-append, since that is what is documented
to work with HBase 0.90.3. I reused the dfs.datanode.max.xcievers to indicate the thread pool
size, which is probably cheating.
I tested this patch with YCSB workloadb on 3 AMD and 2 Intel systems I have handy. It gives
at least equal if not better response times and reduces cpu consumption of the datanode process
by 5-10% depending on the system and load.
Is this a viable approach? If so, I'll forward port it to 0.23 and I can retest if I can find
out which HBase works with 0.23 hdfs.

> DataXceiver per accept seems to be a bottleneck in HBase/YCSB test
> ------------------------------------------------------------------
>
>                 Key: HDFS-2243
>                 URL: https://issues.apache.org/jira/browse/HDFS-2243
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node
>    Affects Versions: 0.23.0
>         Environment: Using Fedora 14 on a quad core phenom system
>            Reporter: Eric Caspole
>            Priority: Minor
>         Attachments: HDFS-2234-branch-0.20-append.patch, datanode-perf-110808.gif
>
>
> I am running the YCSB benchmark against HBase, sometimes against a single node, sometimes
against a cluster of 6 systems. As the load increases into thousands of TPS, especially on
the single node, I can see that the datanode runs very high system time and seems to be bottlenecked
by how fast it can create the threads to handle the new connections in DataXceiverServer.run.
By "perf top" I can see the process spends about 12% of all its time in pthread_create, and
in hprof profiles I can see there are tens of thousands of threads created in just a few minutes
of test execution.
> Does anyone else observe this bottleneck? Is there a major challenge to using a thread
pool of DataXceivers in this situation?

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