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https://issues.apache.org/jira/browse/KAFKA-208?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13152122#comment-13152122
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Jay Kreps commented on KAFKA-208:
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Ah, I see, now. So if I understand your need you actually have a very large
number of topics (say a thousand) so the reason for splitting the register and
poll calls is to avoid sending the topic names each time. I think the problem
with a separate register call is how to manage that metadata on the server. I
would be concerned about something that had to be manually deallocated because
it is possible for the client to leak server resources. Presumably with enough
support it could somehow be tied to the life of the socket that created it...so
maybe each socket could only register at most one interest set and that would
be deallocated if that socket closed.
> Efficient polling mechanism for many topics
> -------------------------------------------
>
> Key: KAFKA-208
> URL: https://issues.apache.org/jira/browse/KAFKA-208
> Project: Kafka
> Issue Type: New Feature
> Reporter: Taylor Gautier
>
> Currently, the way to poll many topics is to submit a request for each one in
> turn, and read the responses. Especially if there are few messages delivered
> on many topics, the network overhead to implement this scheme can far
> outweigh the bandwidth of the actual messages delivered.
> Effectively, for topics A, B, C the request/response scheme is the following:
> -> Request A offset a
> -> Request B offset b
> -> Request C offset c
> <- no messages
> <- 1 message offset b
> <- no messages
> -> Request A offset a
> -> Request B offset b'
> -> Request C offset c
> <- no messages
> <- no messages
> <- no messages
> etc.
> I propose a more efficient mechanism which works a bit like epoll in that the
> client can register interest in a particular topic. There are many options
> for the implementation, but the one I suggest goes like so:
> -> Register interest A offset a
> -> Register interest B offset b
> -> Register interest C offset c
> -> Next message (null)
> <- messages for B (1 message)
> -> Next message (topic B offset b')
> <- no messages
> -> Unregister Interest C
> ...
> It is possible to implement the "Next Message" request as either blocking or
> non-blocking. I suggest that the request format include space for the
> timeout, which if set to 0 will be a nonblocking response, and if set to
> anything other than 0, will block for at most timeout ms.
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