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https://issues.apache.org/jira/browse/KAFKA-642?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jay Kreps updated KAFKA-642:
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Attachment: KAFKA-642-v2.patch
I should clarify that my goal here is to make the most minimal change that
fixes the client protocol for at least the user-facing apis. I also wussed out
on trying to generalize offsetrequest/response. Basically I think trying those
things at these point would just take and we are trying to stabalize and
release.
So I made some of the changes you recommend, but some I think are bigger, and
my hope was to hold off on those.
For example my goal is not to implement correlation id, just add it to the
protocol. To properly handle correlation id we need to make it so that we have
a single counter across all requests on a single connection which is hard to do
right now. I have some thoughts on generalizing some of our serialization and
request handling stuff which I started to discuss in KAFKA-643. All I want to
do now is fix as much of the protocol as I can while breaking as little as
possible in the process.
1. Agreed, fixed.
2. Ack, I missed the correlation id in OffsetResponse. I had intended to leave
it out of the non-public apis since this was meant to be a minimal change, but
it is easy to add so i will do so. This should simplify future upgrades.
3.1 Yeah, but see above comment.
3.2 I mean properly speaking having a default correlation id doesn't really
make sense does it? Anything other than a per-connection counter is basically a
bug...
4. No, it is a signed int so it should be fine for it to roll over every 4
billion requests per connection, that will take a while.
5. Good point.
6. Done
7. See above comment on correlationId
8. Did it for DefaultEventHandler as that is easy, cowardly not attempting for
consumer.
9.1 Done.
9.2 Deleted, should not duplicate protocol docs.
9.3 I chickened out on this. We will have to do it as a follow-up post 0.8 item.
10.1 Agreed, but this is several weeks of work I think. This is a pretty big
refactoring. Some thoughts on KAFKA-643.
11. Yeah, I mean basically that constructor shouldn't exist at all since it
isn't setting client id either.
> 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, KAFKA-642-v2.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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