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https://issues.apache.org/jira/browse/HDFS-13522?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16834021#comment-16834021
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CR Hota edited comment on HDFS-13522 at 5/6/19 5:28 PM:
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[~surendrasingh] Thanks for your comments.
For implementing a queue similar to FairCallQueue, Handlers have to understand
which downstream namenode a call is meant for and also whether its a
read/write. These aspects of a RPC can be inspected only once the call is
handled at the ClientProtocol implementation layer which callqueue won't have
any visibility into. Since we haven't yet finalized how to solve these, in the
interim we have taken a approach as shown in ShortTerm-Routers+Observer.png.
This short term approach segregates reads from writes and helps us serve
latency sensitive engines such as Presto better. We may try to see if this
could become a defacto model where we expose State of Router as read/write just
as Observer's are designed to do. This would solve read/write problem, and
leave us to focus on isolation of writes across various namenodes.
was (Author: crh):
[~surendrasingh] Thanks for your comments.
For implementing a queue similar to FairCallQueue, Handlers have to understand
which downstream namenode a call is meant for and also whether its a
read/write. These aspects of a RPC can be inspected only once the call is
handled at the ClientProtocol implementation layer which callqueue won't have
any visibility into. Since we haven't yet finalized how to solve these, in the
interim we have taken a approach as shown in ShortTerm-Routers+Observer.png.
> Support observer node from Router-Based Federation
> --------------------------------------------------
>
> Key: HDFS-13522
> URL: https://issues.apache.org/jira/browse/HDFS-13522
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: federation, namenode
> Reporter: Erik Krogen
> Assignee: Chao Sun
> Priority: Major
> Attachments: HDFS-13522.001.patch, Router+Observer RPC clogging.png,
> ShortTerm-Routers+Observer.png
>
>
> Changes will need to occur to the router to support the new observer node.
> One such change will be to make the router understand the observer state,
> e.g. {{FederationNamenodeServiceState}}.
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