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https://issues.apache.org/jira/browse/HADOOP-16268?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16911496#comment-16911496
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Erik Krogen commented on HADOOP-16268:
--------------------------------------
Thanks for the explanation [~crh]. I thought that {{throwBackoff()}} was only
called when {{shouldBackoff()}} returned true, but did not notice this code
block which catches the {{IllegalStateException}}:
{code}
try {
return putRef.get().add(e);
} catch (CallQueueOverflowException ex) {
// queue provided a custom exception that may control if the client
// should be disconnected.
throw ex;
} catch (IllegalStateException ise) {
throwBackoff();
}
{code}
I still think it makes sense to update {{FairCallQueue#add()}} as well. Even if
the feature is primarily intended for use by the router, it should be
consistent across different queue implementations. This may become useful when
reading from standby nodes as well.
> 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
>
>
> 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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