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https://issues.apache.org/jira/browse/HDFS-14090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16855129#comment-16855129
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Erik Krogen commented on HDFS-14090:
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[~crh], I took a look at the design document and think your approach is very
sensible. One issue I considered was that if many clients start posting
requests to subcluster A, the call queue on the router may become full of A
requests thus causing decreased service to subcluster B, but it should continue
to drain quickly as there will still be cluster B handlers available to read
the requests and throw {{StandbyException}} to them. So it would seem this
should not be an issue.
One thing I would prefer to see is an exception used besides
{{StandbyException}}; though practically it accomplishes the correct purpose,
it is semantically incorrect. Really a backoff exception is closer to the
correct semantics.
> RBF: Improved isolation for downstream name nodes.
> --------------------------------------------------
>
> Key: HDFS-14090
> URL: https://issues.apache.org/jira/browse/HDFS-14090
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: CR Hota
> Assignee: CR Hota
> Priority: Major
> Attachments: HDFS-14090-HDFS-13891.001.patch, RBF_ Isolation
> design.pdf
>
>
> Router is a gateway to underlying name nodes. Gateway architectures, should
> help minimize impact of clients connecting to healthy clusters vs unhealthy
> clusters.
> For example - If there are 2 name nodes downstream, and one of them is
> heavily loaded with calls spiking rpc queue times, due to back pressure the
> same with start reflecting on the router. As a result of this, clients
> connecting to healthy/faster name nodes will also slow down as same rpc queue
> is maintained for all calls at the router layer. Essentially the same IPC
> thread pool is used by router to connect to all name nodes.
> Currently router uses one single rpc queue for all calls. Lets discuss how we
> can change the architecture and add some throttling logic for
> unhealthy/slow/overloaded name nodes.
> One way could be to read from current call queue, immediately identify
> downstream name node and maintain a separate queue for each underlying name
> node. Another simpler way is to maintain some sort of rate limiter configured
> for each name node and let routers drop/reject/send error requests after
> certain threshold.
> This won’t be a simple change as router’s ‘Server’ layer would need redesign
> and implementation. Currently this layer is the same as name node.
> Opening this ticket to discuss, design and implement this feature.
>
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