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https://issues.apache.org/jira/browse/KAFKA-1835?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14627400#comment-14627400
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Guozhang Wang commented on KAFKA-1835:
--------------------------------------
Joel, I think you are referring to some pattern like:
{code}
init() {
Future<..> future = partitionsFor(topic);
}
handle(req) {
if (future.ready()) // send this message related to req and all other
buffered ones
else // buffer this event for sending
}
{code}
for event-driven programming right? But I think in this case users would
usually not bother checking if the topic metadata is available or not through
partitionsFor since they are not in a hurry sending the messages anyways, but
rather try-send-otherwise-do-sth like:
{code}
handle(req) {
try {
producer.send(req + previously-buffered messages)
} catch {
// not successful, either drop it or buffer it for next send call
}
}
{code}
I guess what I am trying to argue here is that for users who really want
complete "non-blocking" operations it makes little difference for them to hold
a Future object at hand and check periodically than just handle exceptions
up-front. The same argument stands for buffer-exhausted as well: users usually
do not prefer to check a variable indicating if the buffer is full or not every
time they want to send something without blocking, but rather configure it to
let producers throw exceptions directly and handle them.
> Kafka new producer needs options to make blocking behavior explicit
> -------------------------------------------------------------------
>
> Key: KAFKA-1835
> URL: https://issues.apache.org/jira/browse/KAFKA-1835
> Project: Kafka
> Issue Type: Improvement
> Components: clients
> Affects Versions: 0.8.2.0, 0.8.3, 0.9.0
> Reporter: Paul Pearcy
> Fix For: 0.8.3
>
> Attachments: KAFKA-1835-New-producer--blocking_v0.patch,
> KAFKA-1835.patch
>
> Original Estimate: 504h
> Remaining Estimate: 504h
>
> The new (0.8.2 standalone) producer will block the first time it attempts to
> retrieve metadata for a topic. This is not the desired behavior in some use
> cases where async non-blocking guarantees are required and message loss is
> acceptable in known cases. Also, most developers will assume an API that
> returns a future is safe to call in a critical request path.
> Discussing on the mailing list, the most viable option is to have the
> following settings:
> pre.initialize.topics=x,y,z
> pre.initialize.timeout=x
>
> This moves potential blocking to the init of the producer and outside of some
> random request. The potential will still exist for blocking in a corner case
> where connectivity with Kafka is lost and a topic not included in pre-init
> has a message sent for the first time.
> There is the question of what to do when initialization fails. There are a
> couple of options that I'd like available:
> - Fail creation of the client
> - Fail all sends until the meta is available
> Open to input on how the above option should be expressed.
> It is also worth noting more nuanced solutions exist that could work without
> the extra settings, they just end up having extra complications and at the
> end of the day not adding much value. For instance, the producer could accept
> and queue messages(note: more complicated than I am making it sound due to
> storing all accepted messages in pre-partitioned compact binary form), but
> you're still going to be forced to choose to either start blocking or
> dropping messages at some point.
> I have some test cases I am going to port over to the Kafka producer
> integration ones and start from there. My current impl is in scala, but
> porting to Java shouldn't be a big deal (was using a promise to track init
> status, but will likely need to make that an atomic bool).
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