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https://issues.apache.org/jira/browse/KAFKA-642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13511549#comment-13511549
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Jun Rao commented on KAFKA-642:
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60. What you said makes sense. But from IDE, that call maps to the following api
def map[B, That](f: (A) ⇒ B)(implicit bf: CanBuildFrom[Repr, B, That]): That
instead of
def map[B](f: (A) ⇒ B): Traversable[B]
So, it seems that some soft of implicit conversion is happening. We can keep
the code as it as, as long as we understand how this conversion works.
> Protocol tweaks for 0.8
> -----------------------
>
> Key: KAFKA-642
> URL: https://issues.apache.org/jira/browse/KAFKA-642
> Project: Kafka
> Issue Type: Bug
> Components: core
> Affects Versions: 0.8
> Reporter: Jay Kreps
> Assignee: Jay Kreps
> Priority: Blocker
> Attachments: KAFKA-642-v1.patch, KAFKA-642-v2.patch,
> KAFKA-642-v3.patch, KAFKA-642-v4.patch, KAFKA-642-v6.patch
>
>
> There are a couple of things in the protocol that are not idea. It would be
> good to tweak these for 0.8 so we start clean.
> Here is a set of problems and proposals:
> Problems:
> 1. Correlation id is not used across all the requests. I don't think it can
> work as intended because of this.
> 2. On reflection I am not sure that we need a correlation id field. I think
> that since we need to guarantee that processing is sequential on any
> particular socket we can correlate with a simple queue. (e.g. as the client
> sends messages it adds them to a queue and as it receives responses it just
> correlates to whatever is at the head of the queue).
> 3. The metadata response seems to have a number of problems. Among them is
> that it weirdly repeats all the broker information many times. The response
> includes the ISR, leader (maybe), and the replicas. Each of these repeat all
> the broker information. This is super weird. I think what we should be doing
> here is including all broker information for all brokers and then just having
> the appropriate ids for the isr, leader, and replicas.
> 4. For topic discovery I think we need to support the case where no topics
> are specified in the metadata request and for this return information about
> all topics. I don't think we do this now.
> 5. I don't understand what the creator id is.
> 6. The offset request and response is not fully thought through and should be
> generalized.
> Proposals:
> 1, 2. Correlation id. This is not strictly speaking needed, but it is maybe
> useful for debugging to be able to trace a particular request from client to
> server. So we will extend this across all the requests.
> 3. For metadata response I will try to fix this up by normalizing out the
> broker list and having the isr, replicas, and leader field just have the node
> id.
> 4. This should be uncontroversial and easy to add.
> 5. Let's remove creator id, it isn't used.
> 6. Let's generalize offset request. My proposal is below:
> Rename TopicMetadata API to ClusterMetadata, as this will contain all the
> data that is known cluster-wide. Then let's generalize the offset request to
> be PartitionMetadata--namely stuff about a particular partition on a
> particular server.
> The format of PartitionMetdata would be the following:
> PartitionMetadataRequest => [TopicName [PartitionId MinSegmentTime
> MaxSegmentInfos]]
> TopicName => string
> PartitionId => uint32
> MinSegmentTime => uint64
> MaxSegmentInfos => int32
> PartitionMetadataResponse => [TopicName [PartitionMetadata]]
> TopicName => string
> PartitionMetadata => PartitionId LogSize NumberOfSegments LogEndOffset
> HighwaterMark [SegmentData]
> SegmentData => StartOffset LastModifiedTime
> LogSize => uint64
> NumberOfSegments => int32
> LogEndOffset => int64
> HighwaterMark => int64
> This would be general enough that we could continue to add to it for any new
> pieces of data we need.
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