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From "Jay Kreps (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (KAFKA-642) Protocol tweaks for 0.8
Date Mon, 03 Dec 2012 18:55:58 GMT

     [ https://issues.apache.org/jira/browse/KAFKA-642?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jay Kreps updated KAFKA-642:
----------------------------

    Priority: Blocker  (was: Major)
    
> Protocol tweaks for 0.8
> -----------------------
>
>                 Key: KAFKA-642
>                 URL: https://issues.apache.org/jira/browse/KAFKA-642
>             Project: Kafka
>          Issue Type: Bug
>            Reporter: Jay Kreps
>            Priority: Blocker
>         Attachments: KAFKA-642-v1.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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