Thanks Jay. I'll see if I can put together a more complete response, perhaps as separate threads so that topics don't get entangled. In the mean time, here's a couple responses:
Serialization: you've broken out a sub-thread so i'll reply there. My bias is that I like generics (except for type-erasure) and in particular they make it easy to compose serializers for compound payloads (e.g. when a common header wraps a payload of parameterized type). I'll respond to your 4-options message with an example. Build: I've seen a lot of "maven-compatible" build systems produce "artifacts" that aren't really artifacts - no embedded POM or, worst, malformed POM. I know the sbt-generated artifacts were this way - onus is on me to see what gradle is spitting out and what a maven build might look like. Maven may be old and boring, but it gets out of the way and integrates really seamlessly with a lot of IDEs. When some scala projects I was working on in the fall of 2011 switched from sbt to maven, build became a non-issue. Config: Not a big deal and no, I don't think a dropwizard dependency is appropriate. I do like using simple entity beans (POJO's not j2EE) for configuration, especially if they can be marshalled without annotation by Jackson. I only mentioned the dropwizard-extras because it has some entity bean versions of the ZK and Kafka configs. Domain-packaging: Also not a big deal - it's what's expected and it's pretty free in most IDE's. The advantages I see is that it is clear whether something is from the Apache Kafka project and whether something is from another org and related to Kafka. That said, nothing really enforces it. Futures: I'll see if I can create some examples to demonstrate Future making interop easier. Regards, C On Fri, Jan 24, 2014 at 4:36 PM, Jay Kreps <jay.kr...@gmail.com> wrote: > Hey Clark, > > - Serialization: Yes I agree with these though I don't consider the loss of > generics a big issue. I'll try to summarize what I would consider the best > alternative api with raw byte[]. > > - Maven: We had this debate a few months back and the consensus was gradle. > Is there a specific issue with the poms gradle makes? I am extremely loath > to revisit the issue as build issues are a recurring thing and no one ever > agrees and ultimately our build needs are very simple. > > - Config: I'm not sure if I follow the point. Are you saying we should use > something in dropwizard for config? One principle here is to try to remove > as many client dependencies as possible as we inevitably run into terrible > compatibility issues with users who use the same library or its > dependencies at different versions. Or are you talking about maintaining > compatibility with existing config parameters? I think as much as a config > in the existing client makes sense it should have the same name (I was a > bit sloppy about that so I'll fix any errors there). There are a few new > things and we should give those reasonable defaults. I think config is > important so I'll start a thread on the config package in there. > > - org.apache.kafka: We could do this. I always considered it kind of an odd > thing Java programmers do that has no real motivation (but I could be > re-educated!). I don't think it ends up reducing naming conflicts in > practice and it adds a lot of noise and nested directories. Is there a > reason you prefer this or just to be more standard? > > - Future: Basically I didn't see any particular advantage. The cancel() > method doesn't really make sense so probably wouldn't work. Likewise I > dislike the checked exceptions it requires. Basically I just wrote out some > code examples and it seemed cleaner with a special purpose object. I wasn't > actually aware of plans for improved futures in java 8 or the other > integrations. Maybe you could elaborate on this a bit and show how it would > be used? Sounds promising, I just don't know a lot about it. > > -Jay > > > On Fri, Jan 24, 2014 at 3:30 PM, Clark Breyman <cl...@breyman.com> wrote: > > > Jay - Thanks for the call for comments. Here's some initial input: > > > > - Make message serialization a client responsibility (making all messages > > byte[]). Reflection-based loading makes it harder to use generic codecs > > (e.g. Envelope<PREFIX, DATA, SUFFIX>) or build up codec > programmatically. > > Non-default partitioning should require an explicit partition key. > > > > - I really like the fact that it will be native Java. Please consider > using > > native maven and not sbt, gradle, ivy, etc as they don't reliably play > nice > > in the maven ecosystem. A jar without a well-formed pom doesn't feel > like a > > real artifact. The pom's generated by sbt et al. are not well formed. > Using > > maven will make builds and IDE integration much smoother. > > > > - Look at Nick Telford's dropwizard-extras package in which he defines > some > > Jackson-compatible POJO's for loading configuration. Seems like your > client > > migration is similar. The config objects should have constructors or > > factories that accept Map<String, String> and Properties for ease of > > migration. > > > > - Would you consider using the org.apache.kafka package for the new API > > (quibble) > > > > - Why create your own futures rather than use > > java.util.concurrent.Future<Long> or similar? Standard futures will play > > nice with other reactive libs and things like J8's ComposableFuture. > > > > Thanks again, > > C > > > > > > > > On Fri, Jan 24, 2014 at 2:46 PM, Roger Hoover <roger.hoo...@gmail.com > > >wrote: > > > > > A couple comments: > > > > > > 1) Why does the config use a broker list instead of discovering the > > brokers > > > in ZooKeeper? It doesn't match the HighLevelConsumer API. > > > > > > 2) It looks like broker connections are created on demand. I'm > wondering > > > if sometimes you might want to flush out config or network connectivity > > > issues before pushing the first message through. > > > > > > Should there also be a KafkaProducer.connect() or .open() method or > > > connectAll()? I guess it would try to connect to all brokers in the > > > BROKER_LIST_CONFIG > > > > > > HTH, > > > > > > Roger > > > > > > > > > On Fri, Jan 24, 2014 at 11:54 AM, Jay Kreps <jay.kr...@gmail.com> > wrote: > > > > > > > As mentioned in a previous email we are working on a > re-implementation > > of > > > > the producer. I would like to use this email thread to discuss the > > > details > > > > of the public API and the configuration. I would love for us to be > > > > incredibly picky about this public api now so it is as good as > possible > > > and > > > > we don't need to break it in the future. > > > > > > > > The best way to get a feel for the API is actually to take a look at > > the > > > > javadoc, my hope is to get the api docs good enough so that it is > > > > self-explanatory: > > > > > > > > > > > > > > http://empathybox.com/kafka-javadoc/index.html?kafka/clients/producer/KafkaProducer.html > > > > > > > > Please take a look at this API and give me any thoughts you may have! > > > > > > > > It may also be reasonable to take a look at the configs: > > > > > > > > > > > > > > http://empathybox.com/kafka-javadoc/kafka/clients/producer/ProducerConfig.html > > > > > > > > The actual code is posted here: > > > > https://issues.apache.org/jira/browse/KAFKA-1227 > > > > > > > > A few questions or comments to kick things off: > > > > 1. We need to make a decision on whether serialization of the user's > > key > > > > and value should be done by the user (with our api just taking > byte[]) > > or > > > > if we should take an object and allow the user to configure a > > Serializer > > > > class which we instantiate via reflection. We take the later approach > > in > > > > the current producer, and I have carried this through to this > > prototype. > > > > The tradeoff I see is this: taking byte[] is actually simpler, the > user > > > can > > > > directly do whatever serialization they like. The complication is > > > actually > > > > partitioning. Currently partitioning is done by a similar plug-in api > > > > (Partitioner) which the user can implement and configure to override > > how > > > > partitions are assigned. If we take byte[] as input then we have no > > > access > > > > to the original object and partitioning MUST be done on the byte[]. > > This > > > is > > > > fine for hash partitioning. However for various types of semantic > > > > partitioning (range partitioning, or whatever) you would want access > to > > > the > > > > original object. In the current approach a producer who wishes to > send > > > > byte[] they have serialized in their own code can configure the > > > > BytesSerialization we supply which is just a "no op" serialization. > > > > 2. We should obsess over naming and make sure each of the class names > > are > > > > good. > > > > 3. Jun has already pointed out that we need to include the topic and > > > > partition in the response, which is absolutely right. I haven't done > > that > > > > yet but that definitely needs to be there. > > > > 4. Currently RecordSend.await will throw an exception if the request > > > > failed. The intention here is that producer.send(message).await() > > exactly > > > > simulates a synchronous call. Guozhang has noted that this is a > little > > > > annoying since the user must then catch exceptions. However if we > > remove > > > > this then if the user doesn't check for errors they won't know one > has > > > > occurred, which I predict will be a common mistake. > > > > 5. Perhaps there is more we could do to make the async callbacks and > > > future > > > > we give back intuitive and easy to program against? > > > > > > > > Some background info on implementation: > > > > > > > > At a high level the primary difference in this producer is that it > > > removes > > > > the distinction between the "sync" and "async" producer. Effectively > > all > > > > requests are sent asynchronously but always return a future response > > > object > > > > that gives the offset as well as any error that may have occurred > when > > > the > > > > request is complete. The batching that is done in the async producer > > only > > > > today is done whenever possible now. This means that the sync > producer, > > > > under load, can get performance as good as the async producer > > > (preliminary > > > > results show the producer getting 1m messages/sec). This works > similar > > to > > > > group commit in databases but with respect to the actual network > > > > transmission--any messages that arrive while a send is in progress > are > > > > batched together. It is also possible to encourage batching even > under > > > low > > > > load to save server resources by introducing a delay on the send to > > allow > > > > more messages to accumulate; this is done using the linger.ms config > > > (this > > > > is similar to Nagle's algorithm in TCP). > > > > > > > > This producer does all network communication asynchronously and in > > > parallel > > > > to all servers so the performance penalty for acks=-1 and waiting on > > > > replication should be much reduced. I haven't done much benchmarking > on > > > > this yet, though. > > > > > > > > The high level design is described a little here, though this is now > a > > > > little out of date: > > > > https://cwiki.apache.org/confluence/display/KAFKA/Client+Rewrite > > > > > > > > -Jay > > > > > > > > > >
