Hi all,
We've been discussing this for a while (about a month) and I think
people have made some great points that improved the proposal. In
particular, adding async and batching was important. I've also been
talking with some end-users who would like to make use of this API.
Once this is in, we can iterate on it before the release, and it will
also unblock a lot of other admin proposals. I think it would be good
to start the vote in a little bit, assuming there are no objections.
best,
Colin
On Wed, Mar 8, 2017, at 17:09, Colin McCabe wrote:
> On Mon, Mar 6, 2017, at 11:55, Ismael Juma wrote:
> > Thanks Colin.
> >
> > I am familiar with the protocol semantics, but we need to document the
> > API
> > for users who don't know the protocol. I still think it would be valuable
> > to have some examples of how the API would be used for common use cases.
>
> Getting the version of all nodes in the cluster:
> Map<Node, NodeApiVersions> nodesToVersions =
> adminClient.listNodes().nodes().thenApply(
> nodes -> adminClient.apiVersions(nodes)).all().get();
>
> Creating a topic:
> adminClient.createTopic(new NewTopic("myNewTopic", 3, (short)
> 3)).all().get();
>
> Validating that a topic can be created (but not creating it):
> adminClient.createTopic(new NewTopic("myNewTopic", 3, (short) 3),
> new CreateTopicOptions().setValidateOnly(true)).all().get();
>
> > For example, say someone creates a topic and then produces to it. What
> > would be the recommended way to do that?
>
> Once the future returned by createTopics has successfully completed, it
> should be possible to produce to the topic.
>
> There are a few warts that are definitely worth calling out. These are
> things that need to be fixed at the protocol layer, so they're outside
> the scope of this KIP. But you made a good point that we need to
> document this well. Here's my list (I wonder if anyone has more?):
>
> * If auto.create.topics.enable is true on the brokers,
> AdminClient#describeTopic(topicName) may create a topic named topicName.
> There are two workarounds: either use AdminClient#listTopics and ensure
> that the topic is present before describing, or disable
> auto.create.topics.enable.
>
> * If delete.topic.enable is false on the brokers,
> AdminClient#deleteTopic(topicName) will mark topicName for deletion, but
> not actually delete it. deleteTopic will return success in this case.
>
> * It may take several seconds after AdminClient#deleteTopic returns
> success for all the brokers to become aware that the topic is gone.
> During this time, AdminClient#listTopics and AdminClient#describeTopic
> may continue to return information about the deleted topic.
>
> best,
> Colin
>
>
> >
> > Ismael
> >
> > On Mon, Mar 6, 2017 at 7:43 PM, Colin McCabe <cmcc...@apache.org> wrote:
> >
> > > On Mon, Mar 6, 2017, at 05:50, Ismael Juma wrote:
> > > > Thanks Colin. It seems like you replied to me accidentally instead of
> > > > the
> > > > list, so leaving your reply below for the benefit of others.
> > >
> > > Thanks, Ismael. I actually realized my mistake right after I sent to
> > > you, and re-posted it to the mailing list instead of sending directly.
> > > Sigh...
> > >
> > > >
> > > > Regarding the disadvantage of having to hunt through the request class,
> > > > don't people have to do that anyway with the Options classes?
> > >
> > > A lot of people will simply choose the default options, until they have
> > > a reason to do otherwise (for example, they want a longer or shorter
> > > timeout, etc.)
> > >
> > > >
> > > > Aside from that, it would be great if the KIP included more detailed
> > > > javadoc for each method including information about potential
> > > > exceptions.
> > >
> > > That's a good question. Because this is an asynchronous API, methods
> > > never throw exceptions. Instead, if you call get() / whenComplete() /
> > > isCompletedExceptionally() / etc. on one of the CompletableFuture
> > > objects, you will get the exception. This is to allow Node.js-style
> > > completion chaining. I will add this explanation to the KIP.
> > >
> > > > I'm particularly interested in what a user can expect if a create topics
> > > > succeeds versus what they can expect if a timeout exception is thrown.
> > > > It
> > > > would be good to consider partial failures as well.
> > >
> > > This is spelled out by KIP-4.
> > >
> > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-4+-+
> > > Command+line+and+centralized+administrative+operations
> > >
> > > Specifically,
> > >
> > > > If a timeout error occurs [in CreateTopic], the topic could still be
> > > > created successfully at a later time. Its up to the client to query
> > > > for the state at that point.
> > >
> > > Since we're specifically not changing the server as part of this KIP,
> > > those semantics will still be in force. Of course, there are plenty of
> > > other exceptions that you can get from CreateTopics that are more
> > > meaningful, such as permission-related or network-related ones. But if
> > > you get a timeout, the operation may or may not have succeeded.
> > >
> > > Could we fix the timeout problem? Sort of. We could implement
> > > something like a retry cache. The brokers would have to maintain a
> > > cache of operations (and their results) which had succeeded or failed.
> > > Then, if an RPC got interrupted after the server had performed it, but
> > > before the client had received the response message, the client could
> > > simply reconnect on another TCP session and ask the broker for the
> > > result of the previous operation. The broker could look up the result
> > > in the cache and re-send it.
> > >
> > > This fix works, but it is very complex. The cache requires space in
> > > memory (and to do it perfectly, you also want to persist the cache to
> > > disk in case the broker restarts and the client re-appears). The fix
> > > also requires the client to wait for an indefinite amount of time for
> > > the server to come back. If the client ever "gives up" and just throws
> > > a timeout exception, we are back to not knowing what happened on the
> > > server.
> > >
> > > In any case, I think we should discuss RPC change in a separate KIP...
> > > the scope is already big enough here. Also, in practice, users have
> > > workarounds for cases where there are timeouts or failures to
> > > communicate.
> > >
> > > best,
> > > Colin
> > >
> > > >
> > > > Ismael
> > > >
> > > > On Fri, Mar 3, 2017 at 9:37 PM, Colin McCabe <cmcc...@apache.org> wrote:
> > > >
> > > > > On Fri, Mar 3, 2017, at 06:41, Ismael Juma wrote:
> > > > > > Hi Colin,
> > > > > >
> > > > > > I still need to do a detailed review, but I have a couple of
> > > > > > comments/questions:
> > > > > >
> > > > > > 1. I am not sure about having the options/response classes as inner
> > > > > > classes
> > > > > > of the interface. It means that file containing the interface will
> > > > > > be
> > > > > > huge
> > > > > > eventually. And the classes are not necessarily related either. Why
> > > not
> > > > > > use
> > > > > > a separate package for them?
> > > > >
> > > > > Yeah, I think it's reasonable to make these top-level classes and put
> > > > > them in separate files. We can put them all in
> > > > > org.apache.kafka.clients.admin.
> > > > >
> > > > > >
> > > > > > 2. Can you elaborate on how one decides one goes in the Options
> > > > > > class
> > > > > > versus the first parameter?
> > > > >
> > > > > I guess I think of options as things that you don't have to set. For
> > > > > example, when deleting a topic, you must supply the topic name, but
> > > > > supplying a non-default timeout is optional.
> > > > >
> > > > > > I wonder if it would be simpler to just have a
> > > > > > single parameter. In that case it should probably be called a
> > > Request as
> > > > > > Radai suggested, but that's a separate point and we can discuss it
> > > > > > separately.
> > > > >
> > > > > Hmm. I don't think it would be simpler for users. It would force
> > > > > people who just want to do something simple like delete a topic or get
> > > > > the api version of a single node to go hunting through the request
> > > > > class.
> > > > >
> > > > > best,
> > > > > Colin
> > > > >
> > > > >
> > > > > >
> > > > > > Ismael
> > > > > >
> > > > > > On Thu, Mar 2, 2017 at 1:58 AM, Colin McCabe <cmcc...@apache.org>
> > > wrote:
> > > > > >
> > > > > > > On Wed, Mar 1, 2017, at 15:52, radai wrote:
> > > > > > > > quick comment on the request objects:
> > > > > > > >
> > > > > > > > i see "abstract class NewTopic" and "class
> > > NewTopicWithReplication"
> > > > > and "
> > > > > > > > NewTopicWithReplicaAssignments"
> > > > > > > >
> > > > > > > > 1. since the result object is called CreateTopicResults should
> > > these
> > > > > be
> > > > > > > > called *Request?
> > > > > > >
> > > > > > > Hi radai,
> > > > > > >
> > > > > > > Thanks for taking a look.
> > > > > > >
> > > > > > > I think using the name "request" would be very confusing here,
> > > because
> > > > > > > we have a whole family of internal Request classes such as
> > > > > > > CreateTopicsRequest, TopicMetataRequest, etc. which are used for
> > > RPCs.
> > > > > > >
> > > > > > > > 2. this seems like a suboptimal approach to me. imagine we add a
> > > > > > > > NewTopicWithSecurity, and then we would need
> > > > > > > > NewTopicWithReplicationAndSecurity? (or any composable
> > > "traits").
> > > > > > > > this wont really scale. Wouldnt it be better to have a single
> > > (rather
> > > > > > > complicated)
> > > > > > > > CreateTopicRequest, and use a builder pattern to deal with the
> > > > > compexity
> > > > > > > > and options? like so:
> > > > > > > >
> > > > > > > > CreateTopicRequest req =
> > > > > > > > AdminRequests.newTopic("bob").replicationFactor(2).
> > > > > > > withPartitionAssignment(1,
> > > > > > > > "boker7", "broker10").withOption(...).build();
> > > > > > > >
> > > > > > > > the builder would validate any potentially conflicting options
> > > and
> > > > > would
> > > > > > > > allow piling on the complexity in a more manageable way (note -
> > > my
> > > > > code
> > > > > > > > above intends to demonstrate both a general replication factor
> > > and a
> > > > > > > > specific assignment for a partiocular partition of that topic,
> > > which
> > > > > may
> > > > > > > > be
> > > > > > > > too much freedom).
> > > > > > >
> > > > > > > We don't need to express every optional bell and whistle by
> > > creating a
> > > > > > > subclass. In fact, the proposal already had setConfigs() in the
> > > base
> > > > > > > class, since it applies to every new topic creation.
> > > > > > >
> > > > > > > Thinking about it a little more, though, the subclasses don't
> > > really
> > > > > add
> > > > > > > that much value, so we should probably just have NewTopic and no
> > > > > > > subclasses. I removed the subclasses.
> > > > > > >
> > > > > > > best,
> > > > > > > Colin
> > > > > > >
> > > > > > > >
> > > > > > > > On Wed, Mar 1, 2017 at 1:58 PM, Colin McCabe <cmcc...@apache.org
> > > >
> > > > > wrote:
> > > > > > > >
> > > > > > > > > Hi all,
> > > > > > > > >
> > > > > > > > > Thanks for commenting, everyone. Does anyone have more
> > > questions
> > > > > or
> > > > > > > > > comments, or should we vote? The latest proposal is up at
> > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> > > > > > > 117%3A+Add+a+public+
> > > > > > > > > AdminClient+API+for+Kafka+admin+operations
> > > > > > > > >
> > > > > > > > > best,
> > > > > > > > > Colin
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > On Thu, Feb 16, 2017, at 15:00, Colin McCabe wrote:
> > > > > > > > > > On Thu, Feb 16, 2017, at 14:11, Dong Lin wrote:
> > > > > > > > > > > Hey Colin,
> > > > > > > > > > >
> > > > > > > > > > > Thanks for the update. I have two comments:
> > > > > > > > > > >
> > > > > > > > > > > - I actually think it is simpler and good enough to have
> > > > > per-topic
> > > > > > > API
> > > > > > > > > > > instead of batch-of-topic API. This is different from the
> > > > > argument
> > > > > > > for
> > > > > > > > > > > batch-of-partition API because, unlike operation on topic,
> > > > > people
> > > > > > > > > usually
> > > > > > > > > > > operate on multiple partitions (e.g. seek(), purge()) at a
> > > > > time. Is
> > > > > > > > > there
> > > > > > > > > > > performance concern with per-topic API? I am wondering if
> > > we
> > > > > > > should do
> > > > > > > > > > > per-topic API until there is use-case or performance
> > > benefits
> > > > > of
> > > > > > > > > > > batch-of-topic API.
> > > > > > > > > >
> > > > > > > > > > Yes, there is a performance concern with only supporting
> > > > > operations
> > > > > > > on
> > > > > > > > > > one topic at a time. Jay expressed this in some of his
> > > earlier
> > > > > > > emails
> > > > > > > > > > and some other people did as well. We have cases in mind
> > > > > > > > > > for
> > > > > > > management
> > > > > > > > > > software where many topics are created at once.
> > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > - Currently we have interface "Consumer" and "Producer".
> > > And we
> > > > > > > also
> > > > > > > > > have
> > > > > > > > > > > implementations of these two interfaces as "KafkaConsumer"
> > > and
> > > > > > > > > > > "KafkaProducer". If we follow the same naming pattern,
> > > should
> > > > > we
> > > > > > > have
> > > > > > > > > > > interface "AdminClient" and the implementation
> > > > > "KafkaAdminClient",
> > > > > > > > > > > instead
> > > > > > > > > > > of the other way around?
> > > > > > > > > >
> > > > > > > > > > That's a good point. We should do that for consistency.
> > > > > > > > > >
> > > > > > > > > > best,
> > > > > > > > > > Colin
> > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > Dong
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > On Thu, Feb 16, 2017 at 10:19 AM, Colin McCabe <
> > > > > cmcc...@apache.org
> > > > > > > >
> > > > > > > > > > > wrote:
> > > > > > > > > > >
> > > > > > > > > > > > Hi all,
> > > > > > > > > > > >
> > > > > > > > > > > > So I think people have made some very good points so
> > > > > > > > > > > > far.
> > > > > There
> > > > > > > > > seems
> > > > > > > > > > > > to be agreement that we need to have explicit batch APIs
> > > for
> > > > > the
> > > > > > > > > sake of
> > > > > > > > > > > > efficiency, so I added that back.
> > > > > > > > > > > >
> > > > > > > > > > > > Contexts seem a little more complex than we thought, so
> > > > > > > > > > > > I
> > > > > removed
> > > > > > > > > that
> > > > > > > > > > > > from the proposal.
> > > > > > > > > > > >
> > > > > > > > > > > > I removed the Impl class. Instead, we now have a
> > > > > > > KafkaAdminClient
> > > > > > > > > > > > interface and an AdminClient implementation. I think
> > > this
> > > > > > > matches
> > > > > > > > > our
> > > > > > > > > > > > other code better, as Jay commented.
> > > > > > > > > > > >
> > > > > > > > > > > > Each call now has an "Options" object that is passed in.
> > > > > This
> > > > > > > will
> > > > > > > > > > > > allow us to easily add new parameters to the calls
> > > without
> > > > > having
> > > > > > > > > tons
> > > > > > > > > > > > of function overloads. Similarly, each call now has a
> > > > > Results
> > > > > > > > > object,
> > > > > > > > > > > > which will let us easily extend the results we are
> > > returning
> > > > > if
> > > > > > > > > needed.
> > > > > > > > > > > >
> > > > > > > > > > > > Many people made the point that Java 7 Futures are not
> > > that
> > > > > > > useful,
> > > > > > > > > but
> > > > > > > > > > > > Java 8 CompletableFutures are. With CompletableFutures,
> > > you
> > > > > can
> > > > > > > > > chain
> > > > > > > > > > > > calls, adapt them, join them-- basically all the stuff
> > > > > people are
> > > > > > > > > doing
> > > > > > > > > > > > in Node.js and Twisted Python. Java 7 Futures don't
> > > really
> > > > > let
> > > > > > > you
> > > > > > > > > do
> > > > > > > > > > > > anything but poll for a value or block. So I felt that
> > > it
> > > > > was
> > > > > > > > > better to
> > > > > > > > > > > > just go with a CompletableFuture-based API.
> > > > > > > > > > > >
> > > > > > > > > > > > People also made the point that they would like an easy
> > > API
> > > > > for
> > > > > > > > > waiting
> > > > > > > > > > > > on complete success of a batch call. For example, an
> > > > > > > > > > > > API
> > > > > that
> > > > > > > would
> > > > > > > > > > > > fail if even one topic wasn't created in createTopics.
> > > So I
> > > > > > > came up
> > > > > > > > > > > > with Result objects that provide multiple futures that
> > > you
> > > > > can
> > > > > > > wait
> > > > > > > > > on.
> > > > > > > > > > > > You can wait on a future that fires when everything is
> > > > > complete,
> > > > > > > or
> > > > > > > > > you
> > > > > > > > > > > > can wait on futures for individual topics being created.
> > > > > > > > > > > >
> > > > > > > > > > > > I updated the wiki, so please take a look. Note that
> > > this
> > > > > new
> > > > > > > API
> > > > > > > > > > > > requires JDK8. It seems like JDK8 is coming soon,
> > > though,
> > > > > and
> > > > > > > the
> > > > > > > > > > > > disadvantages of sticking to Java 7 are pretty big here,
> > > I
> > > > > think.
> > > > > > > > > > > >
> > > > > > > > > > > > best,
> > > > > > > > > > > > Colin
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > On Mon, Feb 13, 2017, at 11:51, Colin McCabe wrote:
> > > > > > > > > > > > > On Sun, Feb 12, 2017, at 09:21, Jay Kreps wrote:
> > > > > > > > > > > > > > Hey Colin,
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > Thanks for the hard work on this. I know going back
> > > and
> > > > > > > forth on
> > > > > > > > > APIs
> > > > > > > > > > > > is
> > > > > > > > > > > > > > kind of frustrating but we're at the point where
> > > these
> > > > > things
> > > > > > > > > live long
> > > > > > > > > > > > > > enough and are used by enough people that it is
> > > worth the
> > > > > > > pain.
> > > > > > > > > I'm
> > > > > > > > > > > > sure
> > > > > > > > > > > > > > it'll come down in the right place eventually. A
> > > couple
> > > > > > > things
> > > > > > > > > I've
> > > > > > > > > > > > found
> > > > > > > > > > > > > > helped in the past:
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > 1. The burden of evidence needs to fall on the
> > > > > > > complicator.
> > > > > > > > > i.e. if
> > > > > > > > > > > > > > person X thinks the api should be async they need
> > > to
> > > > > > > produce
> > > > > > > > > a set
> > > > > > > > > > > > of
> > > > > > > > > > > > > > common use cases that require this. Otherwise you
> > > are
> > > > > > > > > perpetually
> > > > > > > > > > > > > > having to
> > > > > > > > > > > > > > think "we might need x". I think it is good to
> > > have a
> > > > > > > rule of
> > > > > > > > > > > > "simple
> > > > > > > > > > > > > > until
> > > > > > > > > > > > > > proven insufficient".
> > > > > > > > > > > > > > 2. Make sure we frame things for the intended
> > > > > audience. At
> > > > > > > > > this
> > > > > > > > > > > > point
> > > > > > > > > > > > > > our apis get used by a very broad set of Java
> > > > > engineers.
> > > > > > > This
> > > > > > > > > is a
> > > > > > > > > > > > > > very
> > > > > > > > > > > > > > different audience from our developer mailing
> > > list.
> > > > > These
> > > > > > > > > people
> > > > > > > > > > > > code
> > > > > > > > > > > > > > for a
> > > > > > > > > > > > > > living not necessarily as a passion, and may not
> > > > > > > understand
> > > > > > > > > details
> > > > > > > > > > > > of
> > > > > > > > > > > > > > the
> > > > > > > > > > > > > > internals of our system or even basic things like
> > > > > > > > > multi-threaded
> > > > > > > > > > > > > > programming. I don't think this means we want to
> > > dumb
> > > > > > > things
> > > > > > > > > down,
> > > > > > > > > > > > but
> > > > > > > > > > > > > > rather try really hard to make things truly
> > > > > > > > > > > > > > simple
> > > > > when
> > > > > > > > > possible.
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > Okay here were a couple of comments:
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > 1. Conceptually what is a TopicContext? I think
> > > > > > > > > > > > > > it
> > > > > means
> > > > > > > > > something
> > > > > > > > > > > > > > like
> > > > > > > > > > > > > > TopicAdmin? It is not literally context about
> > > Topics
> > > > > > > right?
> > > > > > > > > What is
> > > > > > > > > > > > > > the
> > > > > > > > > > > > > > relationship of Contexts to clients? Is there a
> > > > > > > threadsafety
> > > > > > > > > > > > > > difference?
> > > > > > > > > > > > > > Would be nice to not have to think about this,
> > > this is
> > > > > > > what I
> > > > > > > > > mean
> > > > > > > > > > > > by
> > > > > > > > > > > > > > "conceptual weight". We introduce a new concept
> > > that
> > > > > is a
> > > > > > > bit
> > > > > > > > > > > > nebulous
> > > > > > > > > > > > > > that
> > > > > > > > > > > > > > I have to figure out to use what could be a
> > > > > > > > > > > > > > simple
> > > > > api.
> > > > > > > I'm
> > > > > > > > > sure
> > > > > > > > > > > > > > you've
> > > > > > > > > > > > > > been through this experience before where you
> > > > > > > > > > > > > > have
> > > > > these
> > > > > > > > > various
> > > > > > > > > > > > > > objects
> > > > > > > > > > > > > > and you're trying to figure out what they
> > > represent
> > > > > (the
> > > > > > > > > connection
> > > > > > > > > > > > to
> > > > > > > > > > > > > > the
> > > > > > > > > > > > > > server? the information to create a connection? a
> > > > > request
> > > > > > > > > session?).
> > > > > > > > > > > > >
> > > > > > > > > > > > > The intention was to provide some grouping of methods,
> > > and
> > > > > > > also a
> > > > > > > > > place
> > > > > > > > > > > > > to put request parameters which were often set to
> > > defaults
> > > > > > > rather
> > > > > > > > > than
> > > > > > > > > > > > > being explicitly set. If it seems complex, we can
> > > > > certainly
> > > > > > > get
> > > > > > > > > rid of
> > > > > > > > > > > > > it.
> > > > > > > > > > > > >
> > > > > > > > > > > > > > 2. We've tried to avoid the Impl naming
> > > convention. In
> > > > > > > > > general the
> > > > > > > > > > > > > > rule
> > > > > > > > > > > > > > has been if there is only going to be one
> > > > > implementation
> > > > > > > you
> > > > > > > > > don't
> > > > > > > > > > > > > > need an
> > > > > > > > > > > > > > interface. If there will be multiple, distinguish
> > > it
> > > > > from
> > > > > > > the
> > > > > > > > > > > > others.
> > > > > > > > > > > > > > The
> > > > > > > > > > > > > > other clients follow this pattern: Producer,
> > > > > > > KafkaProducer,
> > > > > > > > > > > > > > MockProducer;
> > > > > > > > > > > > > > Consumer, KafkaConsumer, MockConsumer.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Good point. Let's change the interface to
> > > > > KafkaAdminClient,
> > > > > > > and
> > > > > > > > > the
> > > > > > > > > > > > > implementation to AdminClient.
> > > > > > > > > > > > >
> > > > > > > > > > > > > > 3. We generally don't use setters or getters as a
> > > > > naming
> > > > > > > > > > > > convention. I
> > > > > > > > > > > > > > personally think mutating the setting in place
> > > seems
> > > > > kind
> > > > > > > of
> > > > > > > > > like
> > > > > > > > > > > > late
> > > > > > > > > > > > > > 90s
> > > > > > > > > > > > > > Java style. I think it likely has thread-safety
> > > > > issues.
> > > > > > > i.e.
> > > > > > > > > even if
> > > > > > > > > > > > > > it is
> > > > > > > > > > > > > > volatile you may not get the value you just set
> > > > > > > > > > > > > > if
> > > > > there
> > > > > > > is
> > > > > > > > > another
> > > > > > > > > > > > > > thread... I actually really liked what you
> > > described
> > > > > as
> > > > > > > your
> > > > > > > > > > > > original
> > > > > > > > > > > > > > idea
> > > > > > > > > > > > > > of having a single parameter object like
> > > > > > > CreateTopicRequest
> > > > > > > > > that
> > > > > > > > > > > > holds
> > > > > > > > > > > > > > all
> > > > > > > > > > > > > > these parameters and defaults. This lets you
> > > evolve
> > > > > the
> > > > > > > api
> > > > > > > > > with all
> > > > > > > > > > > > > > the
> > > > > > > > > > > > > > various combinations of arguments without
> > > overloading
> > > > > > > > > insanity.
> > > > > > > > > > > > After
> > > > > > > > > > > > > > doing
> > > > > > > > > > > > > > literally tens of thousands of remote APIs at
> > > > > LinkedIn we
> > > > > > > > > eventually
> > > > > > > > > > > > > > converged on a rule, which is ultimately every
> > > remote
> > > > > api
> > > > > > > > > needs a
> > > > > > > > > > > > > > single
> > > > > > > > > > > > > > argument object you can add to over time and it
> > > must
> > > > > be
> > > > > > > > > batched.
> > > > > > > > > > > > Which
> > > > > > > > > > > > > > brings me to my next point...
> > > > > > > > > > > > >
> > > > > > > > > > > > > Just to clarify, volatiles were never a part of the
> > > > > proposal.
> > > > > > > I
> > > > > > > > > think
> > > > > > > > > > > > > that context objects or request objects should be used
> > > by a
> > > > > > > single
> > > > > > > > > > > > > thread at a time.
> > > > > > > > > > > > >
> > > > > > > > > > > > > I'm not opposed to request objects, but I think they
> > > raise
> > > > > all
> > > > > > > the
> > > > > > > > > same
> > > > > > > > > > > > > questions as context objects. Basically, the
> > > thread-safety
> > > > > > > issues
> > > > > > > > > need
> > > > > > > > > > > > > to be spelled out and understood by the user, and the
> > > user
> > > > > > > needs
> > > > > > > > > more
> > > > > > > > > > > > > lines of code to make a request. And there will be
> > > people
> > > > > > > trying
> > > > > > > > > to do
> > > > > > > > > > > > > things like re-use request objects when they should
> > > not,
> > > > > and so
> > > > > > > > > forth.
> > > > > > > > > > > > >
> > > > > > > > > > > > > > 4. I agree batch apis are annoying but I suspect
> > > we'll
> > > > > > > end up
> > > > > > > > > adding
> > > > > > > > > > > > > > one. Doing 1000 requests for 1000 operations if
> > > > > creating
> > > > > > > or
> > > > > > > > > deleting
> > > > > > > > > > > > > > will
> > > > > > > > > > > > > > be bad, right? This won't be the common case, but
> > > when
> > > > > > > you do
> > > > > > > > > it it
> > > > > > > > > > > > > > will be
> > > > > > > > > > > > > > a deal-breaker problem. I don't think we should
> > > try
> > > > > to fix
> > > > > > > > > this one
> > > > > > > > > > > > > > behind
> > > > > > > > > > > > > > the scenes.
> > > > > > > > > > > > > > 5. Are we going to do CompletableFuture (which
> > > > > requires
> > > > > > > java
> > > > > > > > > 8) or
> > > > > > > > > > > > > > normal Future? Normal Future is utterly useless
> > > for
> > > > > most
> > > > > > > > > things
> > > > > > > > > > > > other
> > > > > > > > > > > > > > than
> > > > > > > > > > > > > > just calling wait. If we can evolve in place from
> > > > > Future
> > > > > > > to
> > > > > > > > > > > > > > CompletableFuture that is fantastic (we could do
> > > it
> > > > > for
> > > > > > > the
> > > > > > > > > producer
> > > > > > > > > > > > > > too!).
> > > > > > > > > > > > > > My belief was that this was binary incompatible
> > > but I
> > > > > > > > > actually don't
> > > > > > > > > > > > > > know
> > > > > > > > > > > > > > (obviously it's source compatible).
> > > > > > > > > > > > >
> > > > > > > > > > > > > In my testing, replacing a return type with a subclass
> > > of
> > > > > that
> > > > > > > > > return
> > > > > > > > > > > > > type did not break binary compatibility. I haven't
> > > been
> > > > > able
> > > > > > > to
> > > > > > > > > find
> > > > > > > > > > > > > chapter and verse on this from the Java implementers,
> > > > > though.
> > > > > > > > > > > > >
> > > > > > > > > > > > > best,
> > > > > > > > > > > > > Colin
> > > > > > > > > > > > >
> > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > -Jay
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > On Wed, Feb 8, 2017 at 5:00 PM, Colin McCabe <
> > > > > > > cmcc...@apache.org
> > > > > > > > > >
> > > > > > > > > > > > wrote:
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > > Hi all,
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > I made some major revisions to the proposal on the
> > > > > wiki, so
> > > > > > > > > please
> > > > > > > > > > > > check
> > > > > > > > > > > > > > > it out.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > The new API is based on Ismael's suggestion of
> > > grouping
> > > > > > > > > related APIs.
> > > > > > > > > > > > > > > There is only one layer of grouping. I think that
> > > it's
> > > > > > > > > actually
> > > > > > > > > > > > pretty
> > > > > > > > > > > > > > > intuitive. It's also based on the idea of using
> > > > > Futures,
> > > > > > > which
> > > > > > > > > > > > several
> > > > > > > > > > > > > > > people commented that they'd like to see.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > Here's a simple example:
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > AdminClient client = new
> > > AdminClientImpl(myConfig);
> > > > > > > > > > > > > > > > try {
> > > > > > > > > > > > > > > > client.topics().create("foo", 3, (short) 2,
> > > > > > > false).get();
> > > > > > > > > > > > > > > > Collection<String> topicNames =
> > > > > > > > > client.topics().list(false).
> > > > > > > > > > > > get();
> > > > > > > > > > > > > > > > log.info("Found topics: {}",
> > > > > > > Utils.mkString(topicNames,
> > > > > > > > > ", "));
> > > > > > > > > > > > > > > > Collection<Node> nodes =
> > > > > client.nodes().list().get();
> > > > > > > > > > > > > > > > log.info("Found cluster nodes: {}",
> > > > > > > > > Utils.mkString(nodes, ",
> > > > > > > > > > > > "));
> > > > > > > > > > > > > > > > } finally {
> > > > > > > > > > > > > > > > client.close();
> > > > > > > > > > > > > > > > }
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > The good thing is, there is no Try, no 'get'
> > > prefixes,
> > > > > no
> > > > > > > > > messing
> > > > > > > > > > > > with
> > > > > > > > > > > > > > > batch APIs. If there is an error, then
> > > Future#get()
> > > > > > > throws an
> > > > > > > > > > > > > > > ExecutionException which wraps the relevant
> > > exception
> > > > > in
> > > > > > > the
> > > > > > > > > standard
> > > > > > > > > > > > > > > Java way.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > Here's a slightly less simple example:
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > AdminClient client = new
> > > AdminClientImpl(myConfig);
> > > > > > > > > > > > > > > > try {
> > > > > > > > > > > > > > > > List<Future<Void>> futures = new
> > > LinkedList<>();
> > > > > > > > > > > > > > > > for (String topicName: myNewTopicNames) {
> > > > > > > > > > > > > > > > creations.add(client.topics().
> > > > > > > > > > > > > > > > setClientTimeout(30000).setCr
> > > eationConfig(
> > > > > > > > > myTopicConfig).
> > > > > > > > > > > > > > > > create(topicName, 3, (short) 2,
> > > false));
> > > > > > > > > > > > > > > > }
> > > > > > > > > > > > > > > > Futures.waitForAll(futures);
> > > > > > > > > > > > > > > > } finally {
> > > > > > > > > > > > > > > > client.close();
> > > > > > > > > > > > > > > > }
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > I went with Futures because I feel like ought to
> > > have
> > > > > some
> > > > > > > > > option for
> > > > > > > > > > > > > > > doing async. It's a style of programming that has
> > > > > become a
> > > > > > > > > lot more
> > > > > > > > > > > > > > > popular with the rise of Node.js, Twisted python,
> > > etc.
> > > > > etc.
> > > > > > > > > Also, as
> > > > > > > > > > > > > > > Ismael commented, Java 8 CompletableFuture is
> > > going to
> > > > > make
> > > > > > > > > Java's
> > > > > > > > > > > > > > > support for fluent async programming a lot
> > > stronger by
> > > > > > > > > allowing call
> > > > > > > > > > > > > > > chaining and much more.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > If we are going to support async, the simplest
> > > thing is
> > > > > > > just
> > > > > > > > > to make
> > > > > > > > > > > > > > > everything return a future and let people call
> > > get() if
> > > > > > > they
> > > > > > > > > want to
> > > > > > > > > > > > run
> > > > > > > > > > > > > > > synchronously. Having a mix of async and sync
> > > APIs is
> > > > > just
> > > > > > > > > going to
> > > > > > > > > > > > be
> > > > > > > > > > > > > > > confusing and redundant.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > I think we should try to avoid creating single
> > > > > functions
> > > > > > > that
> > > > > > > > > start
> > > > > > > > > > > > > > > multiple requests if we can. It makes things much
> > > > > > > uglier. It
> > > > > > > > > means
> > > > > > > > > > > > > > > that you have to have some kind of request class
> > > that
> > > > > > > wraps up
> > > > > > > > > the
> > > > > > > > > > > > > > > request the user is trying to create, so that you
> > > can
> > > > > > > handle an
> > > > > > > > > > > > array of
> > > > > > > > > > > > > > > those requests. The return value has to be
> > > something
> > > > > like
> > > > > > > > > Map<Node,
> > > > > > > > > > > > > > > Try<Value>> to represent which nodes failed and
> > > > > succeeded.
> > > > > > > > > This is
> > > > > > > > > > > > the
> > > > > > > > > > > > > > > kind of stuff that, in my opinion, makes people
> > > scratch
> > > > > > > their
> > > > > > > > > heads.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > If we need to, we can still get some of the
> > > efficiency
> > > > > > > > > benefits of
> > > > > > > > > > > > batch
> > > > > > > > > > > > > > > APIs by waiting for a millisecond or two before
> > > sending
> > > > > > > out a
> > > > > > > > > topic
> > > > > > > > > > > > > > > create() request to see if other create() requests
> > > > > > > arrive. If
> > > > > > > > > so, we
> > > > > > > > > > > > > > > can coalesce them. It might be better to figure
> > > out if
> > > > > > > this
> > > > > > > > > is an
> > > > > > > > > > > > > > > actual performance issue before implementing it,
> > > > > though.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > I think it would be good to get something out
> > > there,
> > > > > > > annotate
> > > > > > > > > it as
> > > > > > > > > > > > > > > @Unstable, and get feedback from people building
> > > > > against
> > > > > > > trunk
> > > > > > > > > and
> > > > > > > > > > > > using
> > > > > > > > > > > > > > > it. We have removed or changed @Unstable APIs in
> > > > > streams
> > > > > > > > > before, so
> > > > > > > > > > > > I
> > > > > > > > > > > > > > > don't think we should worry that it will get set
> > > > > > > > > > > > > > > in
> > > > > stone
> > > > > > > > > > > > prematurely.
> > > > > > > > > > > > > > > The AdminClient API should get much less developer
> > > use
> > > > > than
> > > > > > > > > anything
> > > > > > > > > > > > in
> > > > > > > > > > > > > > > streams, so changing an unstable API should be
> > > > > > > > > > > > > > > much
> > > > > easier.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > best,
> > > > > > > > > > > > > > > Colin
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > On Wed, Feb 8, 2017, at 07:49, Ismael Juma wrote:
> > > > > > > > > > > > > > > > Thanks for elaborating Jay. I totally agree that
> > > we
> > > > > have
> > > > > > > to
> > > > > > > > > be very
> > > > > > > > > > > > > > > > careful
> > > > > > > > > > > > > > > > in how we use our complexity budget. Easier said
> > > than
> > > > > > > done
> > > > > > > > > when
> > > > > > > > > > > > people
> > > > > > > > > > > > > > > > don't agree on what is complex and what is
> > > simple.
> > > > > :) For
> > > > > > > > > example,
> > > > > > > > > > > > I
> > > > > > > > > > > > > > > > think
> > > > > > > > > > > > > > > > batch APIs are a significant source of
> > > complexity as
> > > > > you
> > > > > > > > > have to
> > > > > > > > > > > > do a
> > > > > > > > > > > > > > > > bunch
> > > > > > > > > > > > > > > > of ceremony to group things before sending the
> > > > > request
> > > > > > > and
> > > > > > > > > error
> > > > > > > > > > > > handling
> > > > > > > > > > > > > > > > becomes more complex due to partial failures
> > > (things
> > > > > like
> > > > > > > > > `Try` or
> > > > > > > > > > > > other
> > > > > > > > > > > > > > > > mechanisms that serve a similar role are then
> > > > > needed).
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > Maybe a way forward is to write API usage
> > > examples to
> > > > > > > help
> > > > > > > > > > > > validate that
> > > > > > > > > > > > > > > > the suggested API is indeed easy to use.
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > Ismael
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > On Wed, Feb 8, 2017 at 4:40 AM, Jay Kreps <
> > > > > > > j...@confluent.io>
> > > > > > > > > > > > wrote:
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > Totally agree on CompletableFuture. Also agree
> > > with
> > > > > > > some
> > > > > > > > > of the
> > > > > > > > > > > > rough
> > > > > > > > > > > > > > > edges
> > > > > > > > > > > > > > > > > on the Consumer.
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > I don't have much of a leg to stand on with
> > > > > > > > > > > > > > > > > the
> > > > > > > splitting
> > > > > > > > > vs not
> > > > > > > > > > > > > > > splitting
> > > > > > > > > > > > > > > > > thing, really hard to argue one or the other
> > > > > > > > > > > > > > > > > is
> > > > > > > better. I
> > > > > > > > > guess
> > > > > > > > > > > > the one
> > > > > > > > > > > > > > > > > observation in watching us try to make good
> > > public
> > > > > apis
> > > > > > > > > over the
> > > > > > > > > > > > years
> > > > > > > > > > > > > > > is I
> > > > > > > > > > > > > > > > > am kind of in favor of a particular kind of
> > > > > simple. In
> > > > > > > > > > > > particular I
> > > > > > > > > > > > > > > think
> > > > > > > > > > > > > > > > > since the bar is sooo high in support and docs
> > > and
> > > > > the
> > > > > > > > > community
> > > > > > > > > > > > of
> > > > > > > > > > > > > > > users
> > > > > > > > > > > > > > > > > so broad in the range of their capabilities,
> > > > > > > > > > > > > > > > > it
> > > > > makes
> > > > > > > it so
> > > > > > > > > > > > there is a
> > > > > > > > > > > > > > > lot
> > > > > > > > > > > > > > > > > of value in dead simple interfaces that don't
> > > have
> > > > > a
> > > > > > > lot of
> > > > > > > > > > > > conceptual
> > > > > > > > > > > > > > > > > weight, don't introduce a lot of new classes
> > > > > > > > > > > > > > > > > or
> > > > > > > concepts or
> > > > > > > > > > > > general
> > > > > > > > > > > > > > > > > patterns that must be understood to use them
> > > > > > > correctly. So
> > > > > > > > > > > > things like
> > > > > > > > > > > > > > > > > nesting, or the Try class, or async apis, or
> > > even
> > > > > just
> > > > > > > a
> > > > > > > > > complex
> > > > > > > > > > > > set of
> > > > > > > > > > > > > > > > > classes representing arguments or return
> > > > > > > > > > > > > > > > > values
> > > > > kind of
> > > > > > > > > all stack
> > > > > > > > > > > > > > > > > conceptual burdens on the user to figure out
> > > > > correct
> > > > > > > > > usage. So
> > > > > > > > > > > > like,
> > > > > > > > > > > > > > > for
> > > > > > > > > > > > > > > > > example, the Try class is very elegant and
> > > > > represents a
> > > > > > > > > whole
> > > > > > > > > > > > > > > generalized
> > > > > > > > > > > > > > > > > class of possibly completed actions, but the
> > > flip
> > > > > side
> > > > > > > is
> > > > > > > > > maybe
> > > > > > > > > > > > I'm
> > > > > > > > > > > > > > > just a
> > > > > > > > > > > > > > > > > working guy who needs to list his kafka topics
> > > but
> > > > > > > doesn't
> > > > > > > > > know
> > > > > > > > > > > > Rust,
> > > > > > > > > > > > > > > take
> > > > > > > > > > > > > > > > > pity on me! :-)
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > Nit picking aside, super excited to see us
> > > > > progress on
> > > > > > > > > this.
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > -Jay
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > On Tue, Feb 7, 2017 at 3:46 PM Ismael Juma <
> > > > > > > > > ism...@juma.me.uk>
> > > > > > > > > > > > wrote:
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > Hi Jay,
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > Thanks for the feedback. Comments inline.
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > On Tue, Feb 7, 2017 at 8:18 PM, Jay Kreps <
> > > > > > > > > j...@confluent.io>
> > > > > > > > > > > > wrote:
> > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > - I think it would be good to not use
> > > "get"
> > > > > as
> > > > > > > the
> > > > > > > > > prefix
> > > > > > > > > > > > for
> > > > > > > > > > > > > > > things
> > > > > > > > > > > > > > > > > > > making remote calls. We've tried to
> > > avoid
> > > > > the
> > > > > > > java
> > > > > > > > > getter
> > > > > > > > > > > > > > > convention
> > > > > > > > > > > > > > > > > > > entirely (see code style guide), but
> > > > > > > > > > > > > > > > > > > for
> > > > > remote
> > > > > > > > > calls in
> > > > > > > > > > > > > > > particular
> > > > > > > > > > > > > > > > > it
> > > > > > > > > > > > > > > > > > > kind
> > > > > > > > > > > > > > > > > > > of blurs the line between field access
> > > and
> > > > > > > remote
> > > > > > > > > RPC in
> > > > > > > > > > > > a way
> > > > > > > > > > > > > > > that
> > > > > > > > > > > > > > > > > > > leads
> > > > > > > > > > > > > > > > > > > people to trouble. What about, e.g.,
> > > > > > > > > fetchAllGroups() vs
> > > > > > > > > > > > > > > > > > getAllGroups().
> > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > Agreed that we should avoid the `get` prefix
> > > for
> > > > > > > remote
> > > > > > > > > calls.
> > > > > > > > > > > > There
> > > > > > > > > > > > > > > are
> > > > > > > > > > > > > > > > > a
> > > > > > > > > > > > > > > > > > few possible prefixes for the read
> > > operations:
> > > > > list,
> > > > > > > > > fetch,
> > > > > > > > > > > > describe.
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > - I think futures and callbacks are a
> > > bit
> > > > > of a
> > > > > > > pain
> > > > > > > > > to
> > > > > > > > > > > > use. I'd
> > > > > > > > > > > > > > > > > second
> > > > > > > > > > > > > > > > > > > Becket's comment: let's ensure there a
> > > > > common
> > > > > > > use
> > > > > > > > > case
> > > > > > > > > > > > > > > motivating
> > > > > > > > > > > > > > > > > > these
> > > > > > > > > > > > > > > > > > > that wouldn't be just as easily
> > > satisfied
> > > > > with
> > > > > > > batch
> > > > > > > > > > > > operations
> > > > > > > > > > > > > > > > > (which
> > > > > > > > > > > > > > > > > > > we
> > > > > > > > > > > > > > > > > > > seem to have at least for some things).
> > > In
> > > > > > > terms of
> > > > > > > > > > > > flexibility
> > > > > > > > > > > > > > > > > > > Callbacks >
> > > > > > > > > > > > > > > > > > > Futures > Batch Ops but I think in
> > > terms of
> > > > > > > > > usability it
> > > > > > > > > > > > is the
> > > > > > > > > > > > > > > > > exact
> > > > > > > > > > > > > > > > > > > opposite so let's make sure we have
> > > worked
> > > > > out
> > > > > > > how
> > > > > > > > > the
> > > > > > > > > > > > API will
> > > > > > > > > > > > > > > be
> > > > > > > > > > > > > > > > > > used
> > > > > > > > > > > > > > > > > > > before deciding. In particular I think
> > > java
> > > > > > > Futures
> > > > > > > > > are
> > > > > > > > > > > > often an
> > > > > > > > > > > > > > > > > > > uncomfortable half-way point since
> > > calling
> > > > > > > get() and
> > > > > > > > > > > > blocking
> > > > > > > > > > > > > > > the
> > > > > > > > > > > > > > > > > > > thread is
> > > > > > > > > > > > > > > > > > > often not what you want for chaining
> > > > > sequences
> > > > > > > of
> > > > > > > > > > > > operations in
> > > > > > > > > > > > > > > a
> > > > > > > > > > > > > > > > > > truly
> > > > > > > > > > > > > > > > > > > async way, so 99% of people just use
> > > > > > > > > > > > > > > > > > > the
> > > > > future
> > > > > > > as
> > > > > > > > > a way
> > > > > > > > > > > > to
> > > > > > > > > > > > > > > batch
> > > > > > > > > > > > > > > > > > calls.
> > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > We should definitely figure out how the APIs
> > > are
> > > > > > > going
> > > > > > > > > to be
> > > > > > > > > > > > used
> > > > > > > > > > > > > > > before
> > > > > > > > > > > > > > > > > > deciding. I agree that callbacks are
> > > definitely
> > > > > > > painful
> > > > > > > > > and
> > > > > > > > > > > > there's
> > > > > > > > > > > > > > > > > little
> > > > > > > > > > > > > > > > > > reason to expose them in a modern API unless
> > > it's
> > > > > > > meant
> > > > > > > > > to be
> > > > > > > > > > > > very
> > > > > > > > > > > > > > > low
> > > > > > > > > > > > > > > > > > level. When it comes to Futures, I think
> > > > > > > > > > > > > > > > > > it's
> > > > > > > important
> > > > > > > > > to
> > > > > > > > > > > > > > > distinguish
> > > > > > > > > > > > > > > > > what
> > > > > > > > > > > > > > > > > > is available in Java 7 and below versus what
> > > is
> > > > > > > > > available from
> > > > > > > > > > > > Java 8
> > > > > > > > > > > > > > > > > > onwards. CompletableFuture makes it much
> > > easier
> > > > > to
> > > > > > > > > > > > compose/chain
> > > > > > > > > > > > > > > > > operations
> > > > > > > > > > > > > > > > > > (in a similar vein to java.util.Stream, our
> > > own
> > > > > > > Streams
> > > > > > > > > API,
> > > > > > > > > > > > etc.)
> > > > > > > > > > > > > > > and it
> > > > > > > > > > > > > > > > > > gives you the ability to register callbacks
> > > if
> > > > > you
> > > > > > > > > really want
> > > > > > > > > > > > to
> > > > > > > > > > > > > > > > > (avoiding
> > > > > > > > > > > > > > > > > > the somewhat odd situation in the Producer
> > > where
> > > > > we
> > > > > > > > > return a
> > > > > > > > > > > > Future
> > > > > > > > > > > > > > > _and_
> > > > > > > > > > > > > > > > > > allow you to pass a callback).
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > - Personally I don't think splitting
> > > > > > > > > > > > > > > > > > > the
> > > > > admin
> > > > > > > > > methods up
> > > > > > > > > > > > > > > actually
> > > > > > > > > > > > > > > > > > makes
> > > > > > > > > > > > > > > > > > > things more usable. It just makes you
> > > have
> > > > > to
> > > > > > > dig
> > > > > > > > > through
> > > > > > > > > > > > our
> > > > > > > > > > > > > > > > > > > hierarchy. I
> > > > > > > > > > > > > > > > > > > think a flat class with a bunch of
> > > > > operations
> > > > > > > (like
> > > > > > > > > the
> > > > > > > > > > > > consumer
> > > > > > > > > > > > > > > > > api)
> > > > > > > > > > > > > > > > > > is
> > > > > > > > > > > > > > > > > > > probably the easiest for people to grok
> > > and
> > > > > find
> > > > > > > > > things
> > > > > > > > > > > > on. I am
> > > > > > > > > > > > > > > > > kind
> > > > > > > > > > > > > > > > > > > of a
> > > > > > > > > > > > > > > > > > > dumb PHP programmer at heart, though.
> > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > I am not sure it's fair to compare the
> > > > > AdminClient
> > > > > > > with
> > > > > > > > > the
> > > > > > > > > > > > > > > Consumer. The
> > > > > > > > > > > > > > > > > > former has APIs for a bunch of unrelated
> > > > > > > > > > > > > > > > > > APIs
> > > > > > > (topics,
> > > > > > > > > ACLs,
> > > > > > > > > > > > configs,
> > > > > > > > > > > > > > > > > > consumer groups, delegation tokens,
> > > > > > > > > > > > > > > > > > preferred
> > > > > leader
> > > > > > > > > election,
> > > > > > > > > > > > > > > partition
> > > > > > > > > > > > > > > > > > reassignment, etc.) where the latter is
> > > pretty
> > > > > > > > > specialised.
> > > > > > > > > > > > For each
> > > > > > > > > > > > > > > of
> > > > > > > > > > > > > > > > > the
> > > > > > > > > > > > > > > > > > resources, you may have 3-4 operations, it
> > > will
> > > > > get
> > > > > > > > > confusing
> > > > > > > > > > > > fast.
> > > > > > > > > > > > > > > Also,
> > > > > > > > > > > > > > > > > > do you really think an API that has one
> > > level of
> > > > > > > > > grouping will
> > > > > > > > > > > > mean
> > > > > > > > > > > > > > > that
> > > > > > > > > > > > > > > > > > users have to "dig through our hierarchy"?
> > > > > > > > > > > > > > > > > > Or
> > > > > are you
> > > > > > > > > > > > concerned that
> > > > > > > > > > > > > > > once
> > > > > > > > > > > > > > > > > > we go in that direction, there is a danger
> > > > > > > > > > > > > > > > > > of
> > > > > making
> > > > > > > the
> > > > > > > > > > > > hierarchy
> > > > > > > > > > > > > > > more
> > > > > > > > > > > > > > > > > > complicated?
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > Finally, I am not sure I would use the
> > > consumer
> > > > > as an
> > > > > > > > > example
> > > > > > > > > > > > of
> > > > > > > > > > > > > > > > > something
> > > > > > > > > > > > > > > > > > that is easy to grok. :) The fact that
> > > methods
> > > > > behave
> > > > > > > > > pretty
> > > > > > > > > > > > > > > differently
> > > > > > > > > > > > > > > > > > (some are blocking while others only have an
> > > > > effect
> > > > > > > after
> > > > > > > > > > > > poll) with
> > > > > > > > > > > > > > > no
> > > > > > > > > > > > > > > > > > indication from the type signature or naming
> > > > > > > convention
> > > > > > > > > makes
> > > > > > > > > > > > it
> > > > > > > > > > > > > > > harder,
> > > > > > > > > > > > > > > > > > not easier, to understand.
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > Ismael
> > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > >
> > > > > > >
> > > > >
> > >
