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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9640) RPC Congestion Control with FairCallQueue
Date Fri, 24 Jan 2014 21:11:38 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9640?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13881428#comment-13881428
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Kihwal Lee commented on HADOOP-9640:
------------------------------------

Can low priority requests starve higher priority requests? If a low priority call queue is
full and all reader threads are blocked on put() for adding calls belonging to that queue,
newly arriving higher priority requests won't get processed even if their corresponding queue
is not full.  If the request rate stays greater than service rate for some time in this state,
the listen queue will likely overflow and all types of requests will suffer regardless of
priority. 

> RPC Congestion Control with FairCallQueue
> -----------------------------------------
>
>                 Key: HADOOP-9640
>                 URL: https://issues.apache.org/jira/browse/HADOOP-9640
>             Project: Hadoop Common
>          Issue Type: Improvement
>    Affects Versions: 3.0.0, 2.2.0
>            Reporter: Xiaobo Peng
>              Labels: hdfs, qos, rpc
>         Attachments: MinorityMajorityPerformance.pdf, NN-denial-of-service-updated-plan.pdf,
faircallqueue.patch, faircallqueue2.patch, faircallqueue3.patch, faircallqueue4.patch, faircallqueue5.patch,
faircallqueue6.patch, faircallqueue7_with_runtime_swapping.patch, rpc-congestion-control-draft-plan.pdf
>
>
> Several production Hadoop cluster incidents occurred where the Namenode was overloaded
and failed to respond. 
> We can improve quality of service for users during namenode peak loads by replacing the
FIFO call queue with a [Fair Call Queue|https://issues.apache.org/jira/secure/attachment/12616864/NN-denial-of-service-updated-plan.pdf].
(this plan supersedes rpc-congestion-control-draft-plan).
> Excerpted from the communication of one incident, “The map task of a user was creating
huge number of small files in the user directory. Due to the heavy load on NN, the JT also
was unable to communicate with NN...The cluster became responsive only once the job was killed.”
> Excerpted from the communication of another incident, “Namenode was overloaded by GetBlockLocation
requests (Correction: should be getFileInfo requests. the job had a bug that called getFileInfo
for a nonexistent file in an endless loop). All other requests to namenode were also affected
by this and hence all jobs slowed down. Cluster almost came to a grinding halt…Eventually
killed jobtracker to kill all jobs that are running.”
> Excerpted from HDFS-945, “We've seen defective applications cause havoc on the NameNode,
for e.g. by doing 100k+ 'listStatus' on very large directories (60k files) etc.”



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