Kafka clients in Hadoop ecosystem, Flume, Spark, etc, have found it really difficult to cope up with Kafka releases as they want to support users on different Kafka versions. Capability to retrieve protocol version will go a long way to ease out those pain points. I will be happy to help out with the work on this KIP. @Magnus, thanks for driving this, is it OK if I carry forward the work from here. It will be ideal to have this in 0.10.0.0.
On Mon, Oct 12, 2015 at 9:29 PM, Jay Kreps <j...@confluent.io> wrote: > I wonder if we need to solve the error problem? I think this KIP gives a > descent work around. > > Probably we should have included an error in the response header, but we > debated it at the time decided not to and now it is pretty hard to add > because the headers aren't versioned (d'oh). > > It seems like any other solution is going to be kind of a hack, right? > Sending malformed responses back seems like not a clean solution... > > (Not sure if I was pro- having a top-level error or not, but in any case > the rationale for the decision was that so many of the requests were > per-partition or per-topic or whatever and hence fail or succeed at that > level and this makes it hard to know what the right top-level error code is > and hard for the client to figure out what to do with the top level error > if some of the partitions succeed but there is a top-level error). > > I think actually this new API actually gives a way to handle this > gracefully on the client side by just having clients that want to be > graceful check for support for their version. Clients that do that will > have a graceful message. > > At some point if we're ever reworking the headers we should really consider > (a) versioning them and (b) adding a top-level error code in the response. > But given this would be a big breaking change and this is really just to > give a nicer error message seems like it probably isn't worth it to try to > do something now. > > -Jay > > > > On Mon, Oct 12, 2015 at 8:11 PM, Jiangjie Qin <j...@linkedin.com.invalid> > wrote: > > > I am thinking instead of returning an empty response, it would be better > to > > return an explicit UnsupportedVersionException code. > > > > Today KafkaApis handles the error in the following way: > > 1. For requests/responses using old Scala classes, KafkaApis uses > > RequestOrResponse.handleError() to return an error response. > > 2. For requests/response using Java classes (only JoinGroupRequest and > > Heartbeat now), KafkaApis calls AbstractRequest.getErrorResponse() to > > return an error response. > > > > In KAFKA-2512, I am returning an UnsupportedVersionException for case [1] > > when see an unsupported version. This will put the error code per topic > or > > partition for most of the requests, but might not work all the time. e.g. > > TopicMetadataRequest with an empty topic set. > > > > Case [2] does not quite work for unsupported version, because we will > > thrown an uncaught exception when version is not recognized (BTW this is > a > > bug). Part of the reason is that for some response types, error code is > not > > part of the response level field. > > > > Maybe it worth checking how each response is dealing with error code > today. > > A scan of the response formats gives the following result: > > 1. TopicMetadataResponse - per topic error code, does not work when the > > topic set is empty in the request. > > 2. ProduceResonse - per partition error code. > > 3. OffsetCommitResponse - per partition. > > 4. OffsetFetchResponse - per partition. > > 5. OffsetResponse - per partition. > > 6. FetchResponse - per partition > > 7. ConsumerMetadataResponse - response level > > 8. ControlledShutdownResponse - response level > > 9. JoinGroupResponse - response level > > 10. HearbeatResponse - response level > > 11. LeaderAndIsrResponse - response level > > 12. StopReplicaResponse - response level > > 13. UpdateMetadataResponse - response level > > > > So from the list above it looks for each response we are actually able to > > return an error code, as long as we make sure the topic or partition > won't > > be empty when the error code is at topic or partition level. Luckily in > the > > above list we only need to worry about TopicMetadataResponse. > > > > Maybe error handling is out of the scope of this KIP, but I prefer we > think > > through how to deal with error code for the requests, because there are > > more request types to be added in KAFKA-2464 and future patches. > > > > Thanks, > > > > Jiangjie (Becket) Qin > > > > On Mon, Oct 12, 2015 at 6:04 PM, Jay Kreps <j...@confluent.io> wrote: > > > > > Two quick pieces of feedback: > > > 1. The use of a version of -1 as magical entry dividing between > > deprecated > > > versions is a bit hacky. What about instead having an array of > supported > > > versions and a separate array of deprecated versions. The deprecated > > > versions would always be a subset of the supported versions. Or, > > > alternately, since deprecation has no functional impact and is just a > > > message to developers, we could just leave it out of the protocol and > > just > > > have it in release notes etc. > > > 2. I think including the api name may cause some problems. Currently > the > > > api key is the primary key that we keep consistent but we have actually > > > evolved the english description of the apis as they have changed. The > > only > > > use I can think of for the name would be if people used the logical > name > > > and tried to resolve the api key, but that would be wrong. Not sure if > we > > > actually need the english name, if there is a use case I guess we'll > just > > > have to be very clear that the name is just documentation and can > change > > > any time. > > > > > > -Jay > > > > > > On Fri, Sep 25, 2015 at 2:53 PM, Magnus Edenhill <mag...@edenhill.se> > > > wrote: > > > > > > > Good evening, > > > > > > > > KIP-35 was created to address current and future broker-client > > > > compatibility. > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-35+-+Retrieving+protocol+version > > > > > > > > Summary: > > > > * allow clients to retrieve the broker's protocol version > > > > * make broker handle unknown protocol requests gracefully > > > > > > > > Feedback and comments welcome! > > > > > > > > Regards, > > > > Magnus > > > > > > > > > > -- Regards, Ashish
