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https://issues.apache.org/jira/browse/HADOOP-16268?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16911818#comment-16911818
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CR Hota commented on HADOOP-16268:
----------------------------------

[~xkrogen] Thanks for the comments. Your point is valid. 

Uploaded 002.patch. Added failover trigger in FairCallQueue#add to allow other 
use cases to evolve in the future if needed.
Also added ipc.<port> as the namespace.

[~jojochuang] Thanks for the comments.
There is no faircall queue defaults in hdfs-default, have skipped adding this 
for now too. May be we can create a new jira to update overall documentation 
page itself that explains what this config does.

> Allow custom wrapped exception to be thrown by server if RPC call queue is 
> filled up
> ------------------------------------------------------------------------------------
>
>                 Key: HADOOP-16268
>                 URL: https://issues.apache.org/jira/browse/HADOOP-16268
>             Project: Hadoop Common
>          Issue Type: Improvement
>            Reporter: CR Hota
>            Assignee: CR Hota
>            Priority: Major
>         Attachments: HADOOP-16268.001.patch, HADOOP-16268.002.patch
>
>
> In the current implementation of callqueue manager, 
> "CallQueueOverflowException" exceptions are always wrapping 
> "RetriableException". Through configs servers should be allowed to throw 
> custom exceptions based on new use cases.
> In CallQueueManager.java for backoff the below is done 
> {code:java}
>   // ideally this behavior should be controllable too.
>   private void throwBackoff() throws IllegalStateException {
>     throw CallQueueOverflowException.DISCONNECT;
>   }
> {code}
> Since CallQueueOverflowException only wraps RetriableException clients would 
> end up hitting the same server for retries. In use cases that router supports 
> these overflowed requests could be handled by another router that shares the 
> same state thus distributing load across a cluster of routers better. In the 
> absence of any custom exception, current behavior should be supported.
> In CallQueueOverflowException class a new Standby exception wrap should be 
> created. Something like the below
> {code:java}
>    static final CallQueueOverflowException KEEPALIVE =
>         new CallQueueOverflowException(
>             new RetriableException(TOO_BUSY),
>             RpcStatusProto.ERROR);
>     static final CallQueueOverflowException DISCONNECT =
>         new CallQueueOverflowException(
>             new RetriableException(TOO_BUSY + " - disconnecting"),
>             RpcStatusProto.FATAL);
>     static final CallQueueOverflowException DISCONNECT2 =
>         new CallQueueOverflowException(
>             new StandbyException(TOO_BUSY + " - disconnecting"),
>             RpcStatusProto.FATAL);
> {code}
>  



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