Gwen, I didn't find this in answers above so apologies if this was discussed. It's about the way we would like to handle request versions.
As I understood from Jun's answer we generally should try using the same java object while evolving the request. I believe the only example of evolved request now - OffsetCommitRequest follows this approach. I'm trying to evolve MetadataRequest to the next version as part of KIP-4 and not sure current AbstractRequest api (which is a basis for ported to java requests) is sufficient. The problem is: in order to deserialize bytes into correct correct object you need to know it's version. Suppose KafkaApi serves OffsetCommitRequestV0 and V2 (current). For such cases OffsetCommitRequest class has two constructors: public static OffsetCommitRequest parse(ByteBuffer buffer, int versionId) AND public static OffsetCommitRequest parse(ByteBuffer buffer) The latter one will simply pick the "current" schema version. Now AbstractRequest.getRequest which is an entry point for deserializing request for KafkaApi matches only on RequestHeader.apiKey (and thus uses the second OffsetCommitRequest constructor) which is not sufficient because we also need RequestHeader.apiVersion in case old request version. The same problem appears in AbstractRequest.getErrorResponse(Throwable e) - to construct the right error response object we need to know to which apiVersion to respond. I think this can affect other tasks under KAFKA-1927 - replacing separate RQ/RP, so maybe it makes sense to decide/fix it once. Thanks, Andrii Bieltskyi On Wed, Mar 25, 2015 at 12:42 AM, Gwen Shapira <gshap...@cloudera.com> wrote: > OK, I posted a working patch on KAFKA-2044 and > https://reviews.apache.org/r/32459/diff/. > > There are few decisions there than can be up to discussion (factory method > on AbstractRequestResponse, the new handleErrors in request API), but as > far as support for o.a.k.common requests in core goes, it does what it > needs to do. > > Please review! > > Gwen > > > > On Tue, Mar 24, 2015 at 10:59 AM, Gwen Shapira <gshap...@cloudera.com> > wrote: > > > Hi, > > > > I uploaded a (very) preliminary patch with my idea. > > > > One thing thats missing: > > RequestResponse had handleError method that all requests implemented, > > typically generating appropriate error Response for the request and > sending > > it along. Its used by KafkaApis to handle all protocol errors for valid > > requests that are not handled elsewhere. > > AbstractRequestResponse doesn't have such method. > > > > I can, of course, add it. > > But before I jump into this, I'm wondering if there was another plan on > > handling Api errors. > > > > Gwen > > > > On Mon, Mar 23, 2015 at 6:16 PM, Jun Rao <j...@confluent.io> wrote: > > > >> I think what you are saying is that in RequestChannel, we can start > >> generating header/body for new request types and leave requestObj null. > >> For > >> existing requests, header/body will be null initially. Gradually, we can > >> migrate each type of requests by populating header/body, instead of > >> requestObj. This makes sense to me since it serves two purposes (1) not > >> polluting the code base with duplicated request/response objects for new > >> types of requests and (2) allowing the refactoring of existing requests > to > >> be done in smaller pieces. > >> > >> Could you try that approach and perhaps just migrate one existing > request > >> type (e.g. HeartBeatRequest) as an example? We probably need to rewind > the > >> buffer after reading the requestId when deserializing the header (since > >> the > >> header includes the request id). > >> > >> Thanks, > >> > >> Jun > >> > >> On Mon, Mar 23, 2015 at 4:52 PM, Gwen Shapira <gshap...@cloudera.com> > >> wrote: > >> > >> > I'm thinking of a different approach, that will not fix everything, > but > >> > will allow adding new requests without code duplication (and therefore > >> > unblock KIP-4): > >> > > >> > RequestChannel.request currently takes a buffer and parses it into an > >> "old" > >> > request object. Since the objects are byte-compatibly, we should be > >> able to > >> > parse existing requests into both old and new objects. New requests > will > >> > only be parsed into new objects. > >> > > >> > Basically: > >> > val requestId = buffer.getShort() > >> > if (requestId in keyToNameAndDeserializerMap) { > >> > requestObj = RequestKeys.deserializerForKey(requestId)(buffer) > >> > header: RequestHeader = RequestHeader.parse(buffer) > >> > body: Struct = > >> > > >> > ProtoUtils.currentRequestSchema(apiKey).read(buffer).asInstanceOf[Struct] > >> > } else { > >> > requestObj = null > >> > header: RequestHeader = RequestHeader.parse(buffer) > >> > body: Struct = > >> > > >> > ProtoUtils.currentRequestSchema(apiKey).read(buffer).asInstanceOf[Struct] > >> > } > >> > > >> > This way existing KafkaApis will keep working as normal. The new Apis > >> can > >> > implement just the new header/body requests. > >> > We'll do the same on the send-side: BoundedByteBufferSend can have a > >> > constructor that takes header/body instead of just a response object. > >> > > >> > Does that make sense? > >> > > >> > Once we have this in, we can move to: > >> > * Adding the missing request/response to the client code > >> > * Replacing requests that can be replaced > >> > > >> > It will also make life easier by having us review and tests smaller > >> chunks > >> > of work (the existing patch is *huge* , touches nearly every core > >> component > >> > and I'm not done yet...) > >> > > >> > Gwen > >> > > >> > > >> > > >> > > >> > On Sun, Mar 22, 2015 at 10:24 PM, Jay Kreps <jay.kr...@gmail.com> > >> wrote: > >> > > >> > > Ack, yeah, forgot about that. > >> > > > >> > > It's not just a difference of wrappers. The server side actually > sends > >> > the > >> > > bytes lazily using FileChannel.transferTo. We need to make it > >> possible to > >> > > carry over that optimization. In some sense what we want to be able > >> to do > >> > > is set a value to a Send instead of a ByteBuffer. > >> > > > >> > > Let me try to add that support to the protocol definition stuff, > will > >> > > probably take me a few days to free up time. > >> > > > >> > > -Jay > >> > > > >> > > On Sun, Mar 22, 2015 at 7:44 PM, Gwen Shapira < > gshap...@cloudera.com> > >> > > wrote: > >> > > > >> > > > In case anyone is still following this thread, I need a bit of > help > >> :) > >> > > > > >> > > > The old FetchResponse.PartitionData included a MessageSet object. > >> > > > The new FetchResponse.PartitionData includes a ByteBuffer. > >> > > > > >> > > > However, when we read from logs, we return a MessageSet, and as > far > >> as > >> > I > >> > > > can see, these can't be converted to ByteBuffers (at least not > >> without > >> > > > copying their data). > >> > > > > >> > > > Did anyone consider how to reconcile the MessageSets with the new > >> > > > FetchResponse objects? > >> > > > > >> > > > Gwen > >> > > > > >> > > > > >> > > > On Sat, Mar 21, 2015 at 6:54 PM, Gwen Shapira < > >> gshap...@cloudera.com> > >> > > > wrote: > >> > > > > >> > > > > Note: I'm also treating ZkUtils as if it was a public API (i.e. > >> > > > converting > >> > > > > objects that are returned into o.a.k.common equivalents but not > >> > > changing > >> > > > > ZkUtils itself). > >> > > > > I know its not public, but I suspect I'm not the only developer > >> here > >> > > who > >> > > > > has tons of external code that uses it. > >> > > > > > >> > > > > Gwen > >> > > > > > >> > > > > On Wed, Mar 18, 2015 at 5:48 PM, Gwen Shapira < > >> gshap...@cloudera.com > >> > > > >> > > > > wrote: > >> > > > > > >> > > > >> We can't rip them out completely, unfortunately - the > >> SimpleConsumer > >> > > > uses > >> > > > >> them. > >> > > > >> > >> > > > >> So we'll need conversion at some point. I'll try to make the > >> > > > >> conversion point "just before hitting a public API that we > can't > >> > > > >> modify", and hopefully it won't look too arbitrary. > >> > > > >> > >> > > > >> > >> > > > >> > >> > > > >> On Wed, Mar 18, 2015 at 5:24 PM, Jay Kreps < > jay.kr...@gmail.com> > >> > > wrote: > >> > > > >> > I think either approach is okay in the short term. However > our > >> > goal > >> > > > >> should > >> > > > >> > be to eventually get rid of that duplicate code, so if you > are > >> up > >> > > for > >> > > > >> just > >> > > > >> > ripping and cutting that may get us there sooner. > >> > > > >> > > >> > > > >> > -Jay > >> > > > >> > > >> > > > >> > On Wed, Mar 18, 2015 at 5:19 PM, Gwen Shapira < > >> > > gshap...@cloudera.com> > >> > > > >> wrote: > >> > > > >> > > >> > > > >> >> Thanks! > >> > > > >> >> > >> > > > >> >> Another clarification: > >> > > > >> >> The Common request/responses use slightly different > >> > infrastructure > >> > > > >> >> objects: Node instead of Broker, TopicPartition instead of > >> > > > >> >> TopicAndPartition and few more. > >> > > > >> >> > >> > > > >> >> I can write utilities to convert Node to Broker to minimize > >> the > >> > > scope > >> > > > >> >> of the change. > >> > > > >> >> Or I can start replacing Brokers with Nodes across the > board. > >> > > > >> >> > >> > > > >> >> I'm currently taking the second approach - i.e, if > >> > MetadataRequest > >> > > is > >> > > > >> >> now returning Node, I'm changing the entire line of > >> dependencies > >> > to > >> > > > >> >> use Nodes instead of broker. > >> > > > >> >> > >> > > > >> >> Is this acceptable, or do we want to take a more minimal > >> approach > >> > > for > >> > > > >> >> this patch and do a larger replacement as a follow up? > >> > > > >> >> > >> > > > >> >> Gwen > >> > > > >> >> > >> > > > >> >> > >> > > > >> >> > >> > > > >> >> > >> > > > >> >> On Wed, Mar 18, 2015 at 3:32 PM, Jay Kreps < > >> jay.kr...@gmail.com> > >> > > > >> wrote: > >> > > > >> >> > Great. > >> > > > >> >> > > >> > > > >> >> > For (3) yeah I think we should just think through the > >> > end-to-end > >> > > > >> pattern > >> > > > >> >> > for these versioned requests since it seems like we will > >> have a > >> > > > >> number of > >> > > > >> >> > them. The serialization code used as you described gets us > >> to > >> > the > >> > > > >> right > >> > > > >> >> > Struct which the user would then wrap in something like > >> > > > >> ProduceRequest. > >> > > > >> >> > Presumably there would just be one ProduceRequest that > would > >> > > > >> internally > >> > > > >> >> > fill in things like null or otherwise adapt the struct to > a > >> > > usable > >> > > > >> >> object. > >> > > > >> >> > On the response side we would have the version from the > >> request > >> > > to > >> > > > >> use > >> > > > >> >> for > >> > > > >> >> > correct versioning. On question is whether this is enough > or > >> > > > whether > >> > > > >> we > >> > > > >> >> > need to have switches in KafkaApis to do things like > >> > > > >> >> > if(produceRequest.version == 3) > >> > > > >> >> > // do something > >> > > > >> >> > else > >> > > > >> >> > // do something else > >> > > > >> >> > > >> > > > >> >> > Basically it would be good to be able to write a quick > wiki > >> > that > >> > > > was > >> > > > >> like > >> > > > >> >> > "how to add or modify a kafka api" that explained the > right > >> way > >> > > to > >> > > > >> do all > >> > > > >> >> > this. > >> > > > >> >> > > >> > > > >> >> > I don't think any of this necessarily blocks this ticket > >> since > >> > at > >> > > > the > >> > > > >> >> > moment we don't have tons of versions of requests out > there. > >> > > > >> >> > > >> > > > >> >> > -Jay > >> > > > >> >> > > >> > > > >> >> > On Wed, Mar 18, 2015 at 2:50 PM, Gwen Shapira < > >> > > > gshap...@cloudera.com > >> > > > >> > > >> > > > >> >> wrote: > >> > > > >> >> > > >> > > > >> >> >> See inline responses: > >> > > > >> >> >> > >> > > > >> >> >> On Wed, Mar 18, 2015 at 2:26 PM, Jay Kreps < > >> > jay.kr...@gmail.com > >> > > > > >> > > > >> wrote: > >> > > > >> >> >> > Hey Gwen, > >> > > > >> >> >> > > >> > > > >> >> >> > This makes sense to me. > >> > > > >> >> >> > > >> > > > >> >> >> > A couple of thoughts, mostly confirming what you said I > >> > think: > >> > > > >> >> >> > > >> > > > >> >> >> > 1. Ideally we would move completely over to the new > >> style > >> > > of > >> > > > >> >> request > >> > > > >> >> >> > definition for server-side processing, even for the > >> > > internal > >> > > > >> >> >> requests. This > >> > > > >> >> >> > way all requests would have the same header/body > >> struct > >> > > > stuff. > >> > > > >> As > >> > > > >> >> you > >> > > > >> >> >> say > >> > > > >> >> >> > for the internal requests we can just delete the > scala > >> > > code. > >> > > > >> For > >> > > > >> >> the > >> > > > >> >> >> old > >> > > > >> >> >> > clients they will continue to use their old request > >> > > > definitions > >> > > > >> >> until > >> > > > >> >> >> we > >> > > > >> >> >> > eol them. I would propose that new changes will go > >> only > >> > > into > >> > > > >> the > >> > > > >> >> new > >> > > > >> >> >> > request/response objects and the old scala ones will > >> be > >> > > > >> permanently > >> > > > >> >> >> stuck > >> > > > >> >> >> > on their current version until discontinued. So > after > >> > this > >> > > > >> change > >> > > > >> >> >> that old > >> > > > >> >> >> > scala code could be considered frozen. > >> > > > >> >> >> > >> > > > >> >> >> SimpleConsumer is obviously stuck with the old > >> > request/response. > >> > > > >> >> >> > >> > > > >> >> >> The Producers can be converted to the common > >> request/response > >> > > > >> without > >> > > > >> >> >> breaking compatibility. > >> > > > >> >> >> I think we should do this (even though it requires > fiddling > >> > with > >> > > > >> >> >> additional network serialization code), just so we can > >> throw > >> > the > >> > > > old > >> > > > >> >> >> ProduceRequest away. > >> > > > >> >> >> > >> > > > >> >> >> Does that make sense? > >> > > > >> >> >> > >> > > > >> >> >> > >> > > > >> >> >> > 2. I think it would be reasonable to keep all the > >> > requests > >> > > > >> under > >> > > > >> >> >> common, > >> > > > >> >> >> > even though as you point out there is currently no > use > >> > for > >> > > > >> some of > >> > > > >> >> >> them > >> > > > >> >> >> > beyond broker-to-broker communication at the moment. > >> > > > >> >> >> > >> > > > >> >> >> Yep. > >> > > > >> >> >> > >> > > > >> >> >> > 3. We should think a little about how versioning > will > >> > work. > >> > > > >> Making > >> > > > >> >> >> this > >> > > > >> >> >> > convenient on the server side is an important goal > for > >> > the > >> > > > new > >> > > > >> >> style > >> > > > >> >> >> of > >> > > > >> >> >> > request definition. At the serialization level we > now > >> > > handle > >> > > > >> >> >> versioning but > >> > > > >> >> >> > the question we should discuss and work out is how > >> this > >> > > will > >> > > > >> map to > >> > > > >> >> >> the > >> > > > >> >> >> > request objects (which I assume will remain > >> unversioned). > >> > > > >> >> >> > >> > > > >> >> >> The way I see it working (I just started on this, so I > may > >> > have > >> > > > >> gaps): > >> > > > >> >> >> > >> > > > >> >> >> * Request header contains the version > >> > > > >> >> >> * When we read the request, we use > ProtoUtils.requestSchema > >> > > which > >> > > > >> >> >> takes version as a parameter and is responsible to give > us > >> the > >> > > > right > >> > > > >> >> >> Schema, which we use to read the buffer and get the > correct > >> > > > struct. > >> > > > >> >> >> * KafkaApis handlers have the header, so they can use it > to > >> > > access > >> > > > >> the > >> > > > >> >> >> correct fields, build the correct response, etc. > >> > > > >> >> >> > >> > > > >> >> >> Does that sound about right? > >> > > > >> >> >> > >> > > > >> >> >> > >> > > > >> >> >> > 4. Ideally after this refactoring the network > package > >> > > should > >> > > > >> not be > >> > > > >> >> >> > dependent on the individual request objects. The > >> > intention > >> > > is > >> > > > >> that > >> > > > >> >> >> stuff in > >> > > > >> >> >> > kafka.network is meant to be generic network > >> > infrastructure > >> > > > >> that > >> > > > >> >> >> doesn't > >> > > > >> >> >> > know about the particular fetch/produce apis we have > >> > > > >> implemented on > >> > > > >> >> >> top. > >> > > > >> >> >> > >> > > > >> >> >> I'll make a note to validate that this is the case. > >> > > > >> >> >> > >> > > > >> >> >> > > >> > > > >> >> >> > -Jay > >> > > > >> >> >> > > >> > > > >> >> >> > On Wed, Mar 18, 2015 at 11:11 AM, Gwen Shapira < > >> > > > >> gshap...@cloudera.com > >> > > > >> >> > > >> > > > >> >> >> > wrote: > >> > > > >> >> >> > > >> > > > >> >> >> >> Hi Jun, > >> > > > >> >> >> >> > >> > > > >> >> >> >> I was taking a slightly different approach. Let me > know > >> if > >> > it > >> > > > >> makes > >> > > > >> >> >> >> sense to you: > >> > > > >> >> >> >> > >> > > > >> >> >> >> 1. Get the bytes from network (kinda unavoidable...) > >> > > > >> >> >> >> 2. Modify RequestChannel.Request to contain header and > >> body > >> > > > >> (instead > >> > > > >> >> >> >> of a single object) > >> > > > >> >> >> >> 3. Create the head and body from bytes as follow: > >> > > > >> >> >> >> val header: RequestHeader = > >> RequestHeader.parse(buffer) > >> > > > >> >> >> >> val apiKey: Int = header.apiKey > >> > > > >> >> >> >> val body: Struct = > >> > > > >> >> >> >> > >> > > > >> >> >> > >> > > > >> >> > >> > > > >> > >> > > > > >> > > >> > ProtoUtils.currentRequestSchema(apiKey).read(buffer).asInstanceOf[Struct] > >> > > > >> >> >> >> 4. KafkaAPIs will continue getting > >> RequestChannel.Request, > >> > > but > >> > > > >> will > >> > > > >> >> >> >> now have access to body and header separately. > >> > > > >> >> >> >> > >> > > > >> >> >> >> I agree that I need a Request/Response objects that > >> contain > >> > > > only > >> > > > >> the > >> > > > >> >> >> >> body for all requests objects. > >> > > > >> >> >> >> I'm thinking of implementing them in > >> o.a.k.Common.Requests > >> > in > >> > > > >> Java > >> > > > >> >> for > >> > > > >> >> >> >> consistency. > >> > > > >> >> >> >> > >> > > > >> >> >> >> When we are discussing the requests/responses used in > >> > > > >> SimpleConsumer, > >> > > > >> >> >> >> we mean everything used in javaapi, right? > >> > > > >> >> >> >> > >> > > > >> >> >> >> Gwen > >> > > > >> >> >> >> > >> > > > >> >> >> >> > >> > > > >> >> >> >> > >> > > > >> >> >> >> On Wed, Mar 18, 2015 at 9:55 AM, Jun Rao < > >> j...@confluent.io > >> > > > >> > > > >> wrote: > >> > > > >> >> >> >> > Hi, Gwen, > >> > > > >> >> >> >> > > >> > > > >> >> >> >> > I was thinking that we will be doing the following > in > >> > > > >> KAFKA-1927. > >> > > > >> >> >> >> > > >> > > > >> >> >> >> > 1. Get the bytes from network. > >> > > > >> >> >> >> > 2. Use a new generic approach to convert bytes into > >> > request > >> > > > >> >> objects. > >> > > > >> >> >> >> > 2.1 Read the fixed request header (using the util in > >> > > client). > >> > > > >> >> >> >> > 2.2 Based on the request id in the header, > deserialize > >> > the > >> > > > >> rest of > >> > > > >> >> the > >> > > > >> >> >> >> > bytes into a request specific object (using the new > >> java > >> > > > >> objects). > >> > > > >> >> >> >> > 3. We will then be passing a header and an > >> > > > >> AbstractRequestResponse > >> > > > >> >> to > >> > > > >> >> >> >> > KafkaApis. > >> > > > >> >> >> >> > > >> > > > >> >> >> >> > In order to do that, we will need to create similar > >> > > > >> >> request/response > >> > > > >> >> >> >> > objects for internal requests such as StopReplica, > >> > > > >> LeaderAndIsr, > >> > > > >> >> >> >> > UpdateMetadata, ControlledShutdown. Not sure whether > >> they > >> > > > >> should be > >> > > > >> >> >> >> written > >> > > > >> >> >> >> > in java or scala, but perhaps they should be only in > >> the > >> > > core > >> > > > >> >> project. > >> > > > >> >> >> >> > > >> > > > >> >> >> >> > Also note, there are some scala requests/responses > >> used > >> > > > >> directly in > >> > > > >> >> >> >> > SimpleConsumer. Since that's our public api, we > can't > >> > > remove > >> > > > >> those > >> > > > >> >> >> scala > >> > > > >> >> >> >> > objects until the old consumer is phased out. We can > >> > remove > >> > > > the > >> > > > >> >> rest > >> > > > >> >> >> of > >> > > > >> >> >> >> the > >> > > > >> >> >> >> > scala request objects. > >> > > > >> >> >> >> > > >> > > > >> >> >> >> > Thanks, > >> > > > >> >> >> >> > > >> > > > >> >> >> >> > Jun > >> > > > >> >> >> >> > > >> > > > >> >> >> >> > > >> > > > >> >> >> >> > On Tue, Mar 17, 2015 at 6:08 PM, Gwen Shapira < > >> > > > >> >> gshap...@cloudera.com> > >> > > > >> >> >> >> wrote: > >> > > > >> >> >> >> > > >> > > > >> >> >> >> >> Hi, > >> > > > >> >> >> >> >> > >> > > > >> >> >> >> >> I'm starting this thread for the various questions > I > >> run > >> > > > into > >> > > > >> >> while > >> > > > >> >> >> >> >> refactoring the server to use client requests and > >> > > responses. > >> > > > >> >> >> >> >> > >> > > > >> >> >> >> >> Help is appreciated :) > >> > > > >> >> >> >> >> > >> > > > >> >> >> >> >> First question: LEADER_AND_ISR request and > >> STOP_REPLICA > >> > > > >> request > >> > > > >> >> are > >> > > > >> >> >> >> >> unimplemented in the client. > >> > > > >> >> >> >> >> > >> > > > >> >> >> >> >> Do we want to implement them as part of this > >> > refactoring? > >> > > > >> >> >> >> >> Or should we continue using the scala > implementation > >> for > >> > > > >> those? > >> > > > >> >> >> >> >> > >> > > > >> >> >> >> >> Gwen > >> > > > >> >> >> >> >> > >> > > > >> >> >> >> > >> > > > >> >> >> > >> > > > >> >> > >> > > > >> > >> > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > > > > >
