Yeah I'll fix that name. Hmm, yeah, I agree that often you want to be able delay network connectivity until you have started everything up. But at the same time I kind of loath special init() methods because you always forget to call them and get one round of error every time. I wonder if in those cases one could just avoid creating the producer instance until you are ready to connect. Basically if you think of the producer instance as the equivalent of a socket connection or whatever this kind of makes sense.
-Jay On Fri, Jan 24, 2014 at 4:34 PM, Roger Hoover <roger.hoo...@gmail.com>wrote: > Jay, > > Thanks for the explanation. I didn't realize that the broker list was for > bootstrapping and was not required to be a complete list of all brokers > (although I see now that it's clearly stated in the text description of the > parameter). Nonetheless, does it still make sense to make the config > parameter more clear? Instead of BROKER_LIST_CONFIG, it could be something > like BROKER_LIST_INITIAL_CONFIG or BROKER_DISCOVERY_LIST_CONFIG or > BROKER_BOOTSTRAP_LIST_CONFIG? > > I like the idea of proactively checking that at least one broker url is > working and failing fast if it is not. My 2 cents is that it should be > triggered by a method call like initialize() rather than doing it in the > constructor. Sometimes for unit tests or other purposes, you want to be > able to create objects without triggering network dependencies. > > Cheers, > > Roger > > > On Fri, Jan 24, 2014 at 4:13 PM, Jay Kreps <jay.kr...@gmail.com> wrote: > > > Roger, > > > > These are good questions. > > > > 1. The producer since 0.8 is actually zookeeper free, so this is not new > to > > this client it is true for the current client as well. Our experience was > > that direct zookeeper connections from zillions of producers wasn't a > good > > idea for a number of reasons. Our intention is to remove this dependency > > from the consumer as well. The configuration in the producer doesn't need > > the full set of brokers, though, just one or two machines to bootstrap > the > > state of the cluster from--in other words it isn't like you need to > > reconfigure your clients every time you add some servers. This is exactly > > how zookeeper works too--if we used zookeeper you would need to give a > list > > of zk urls in case a particular zk server was down. Basically either way > > you need a few statically configured nodes to go to discover the full > state > > of the cluster. For people who don't like hard coding hosts you can use a > > VIP or dns or something instead. > > > > 2. Yes this is a good point and was a concern I had too--the current > > behavior is that with bad urls the client would start normally and then > > hang trying to fetch metadata when the first message is sent and finally > > give up and throw an exception. This is not ideal. > > > > The challenge is this: we use the bootstrap urls to fetch metadata for > > particular topics but we don't know which until we start getting messages > > for them. We have the option of fetching metadata for all topics but the > > problem is that for a cluster hosting tens of thousands of topics that is > > actually a ton of data. > > > > An alternative that this just made me think of is that we could > proactively > > connect to bootstrap urls sequentially until one succeeds when the > producer > > is first created and fail fast if we can't establish a connection. This > > would not be wasted work as we could use the connection for the metadata > > request when the first message is sent. I like this solution and will > > implement it. So thanks for asking! > > > > -Jay > > > > > > > > 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 > > > > > > > > > >
