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From Boyang Chen <reluctanthero...@gmail.com>
Subject Re: [DISCUSS] KIP-447: Producer scalability for exactly once semantics
Date Mon, 08 Jul 2019 22:18:46 GMT
Hey Guozhang,

I will correct my statement from last email. I don't think the
read_committed (3.a) is necessary to be added to the OffsetFetch request,
as if we are using EOS application, the underlying consumers within the
group should always back off when there is pending offsets.

Let me know if you think this is correct.

On Tue, Jul 2, 2019 at 3:21 PM Boyang Chen <reluctanthero104@gmail.com>
wrote:

> Thank you Guozhang for the questions, inline answers are below.
>
> On Tue, Jul 2, 2019 at 3:14 PM Boyang Chen <reluctanthero104@gmail.com>
> wrote:
>
>> Hey all,
>>
>> I have done a fundamental polish of KIP-447
>> <https://cwiki.apache.org/confluence/display/KAFKA/KIP-447%3A+Producer+scalability+for+exactly+once+semantics>
and
>> written a design doc
>> <https://docs.google.com/document/d/1LhzHGeX7_Lay4xvrEXxfciuDWATjpUXQhrEIkph9qRE/edit#>
depicting
>> internal changes. We stripped off many implementation details from the KIP,
>> and simplified the public changes by a lot. For reviewers, it is highly
>> recommended to fully understand EOS design in KIP-98 and read its
>> corresponding design doc
>> <https://docs.google.com/document/d/11Jqy_GjUGtdXJK94XGsEIK7CP1SnQGdp2eF0wSw9ra8/edit>
if
>> you haven't done so already.
>>
>> Let me know if you found anything confusing around the KIP or the design.
>> Would be happy to discuss in depth.
>>
>> Best,
>> Boyang
>>
>>
>>
>>
>>
>> On Wed, Jun 26, 2019 at 11:00 AM Guozhang Wang <wangguoz@gmail.com>
>> wrote:
>>
>>> 2. The reason we did not expose generation.id from KafkaConsumer public
>>> APIs directly is to abstract this notion from users (since it is an
>>> implementation detail of the rebalance protocol itself, e.g. if user
>>> calls
>>> consumer.assign() they do not need to invoke ConsumerCoordinator and no
>>> need to be aware of generation.id at all).
>>>
>>> On the other hand, with the current proposal the txn.coordiantor did not
>>> know about the latest generation from the source-of-truth
>>> group.coordinator; instead, it will only bump up the generation from the
>>> producer's InitProducerIdRequest only.
>>>
>>> The key here is that GroupCoordinator, when handling
>>> `InitProducerIdRequest
>>>
>> In the new design, we just pass the entire consumer instance into the
> producer through
> #initTransaction, so no public API will be created.
>
>> 3. I agree that if we rely on the group coordinator to block on returning
>>> offset-fetch-response if read-committed is enabled, then we do not need
>>> to
>>> store partition assignment on txn coordinator and therefore it's better
>>> to
>>> still decouple them. For that case we still need to update the KIP wiki
>>> page that includes:
>>>
>>> 3.a. Augment OffsetFetchRequest with the ISOLATION_LEVEL as well.
>>> 3.b. Add new error code in OffsetFetchResponse to let client backoff and
>>> retry if there are pending txns including the interested partitions.
>>> 3.c. Also in the worst case we would let the client be blocked for the
>>> txn.timeout period, and for that rationale we may need to consider
>>> reducing
>>> our default txn.timeout value as well.
>>>
>>> Addressed 3.b and 3.c, will do 3.a.
>
>> 4. According to Colin it seems we do not need to create another KIP and we
>>> can just complete it as part of KIP-117 / KAFKA-5214; and we need to do
>>> some cleanup to have BrokerApiVersion exposed from AdminClient (@Colin
>>> please let use know if you have any concerns exposing it).
>>>
>> I think we no longer need to rely on api version for initialization,
> since we will be using the upgrade.from config anyway.
>
>>
>>> Guozhang
>>>
>>>
>>> On Tue, Jun 25, 2019 at 6:43 PM Jason Gustafson <jason@confluent.io>
>>> wrote:
>>>
>>> > For reference, we have BrokerApiVersionCommand already as a public
>>> > interface. We have a bit of tech debt at the moment because it uses a
>>> > custom AdminClient. It would be nice to clean that up. In general, I
>>> think
>>> > it is reasonable to expose from AdminClient. It can be used by
>>> management
>>> > tools to inspect running Kafka versions for example.
>>> >
>>> > -Jason
>>> >
>>> > On Tue, Jun 25, 2019 at 4:37 PM Boyang Chen <
>>> reluctanthero104@gmail.com>
>>> > wrote:
>>> >
>>> > > Thank you for the context Colin. The groupId was indeed a copy-paste
>>> > error.
>>> > > Our use case here for 447 is (Quoted from Guozhang):
>>> > > '''
>>> > > I think if we can do something else to
>>> > > avoid this config though, for example we can use the embedded
>>> AdminClient
>>> > > to send the APIVersion request upon starting up, and based on the
>>> > returned
>>> > > value decides whether to go to the old code path or the new behavior.
>>> > > '''
>>> > > The benefit we get is to avoid adding a new configuration to make a
>>> > > decision simply base on broker version. If you have concerns with
>>> > exposing
>>> > > ApiVersion for client, we could
>>> > > try to think of alternative solutions too.
>>> > >
>>> > > Boyang
>>> > >
>>> > >
>>> > >
>>> > > On Tue, Jun 25, 2019 at 4:20 PM Colin McCabe <cmccabe@apache.org>
>>> wrote:
>>> > >
>>> > > > kafka.api.ApiVersion is an internal class, not suitable to exposing
>>> > > > through AdminClient.  That class is not even accessible without
>>> having
>>> > > the
>>> > > > broker jars on your CLASSPATH.
>>> > > >
>>> > > > Another question is, what is the groupId parameter doing in the
>>> call?
>>> > > The
>>> > > > API versions are the same no matter what consumer group we use,
>>> right?
>>> > > > Perhaps this was a copy and paste error?
>>> > > >
>>> > > > This is not the first time we have discussed having a method in
>>> > > > AdminClient to retrieve API version information.  In fact, the
>>> original
>>> > > KIP
>>> > > > which created KafkaAdminClient specified an API for fetching
>>> version
>>> > > > information.  It was called apiVersions and it is still there
on
>>> the
>>> > > wiki.
>>> > > > See
>>> > > >
>>> > >
>>> >
>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-117%3A+Add+a+public+AdminClient+API+for+Kafka+admin+operations
>>> > > >
>>> > > > However, this API wasn't ready in time for 0.11.0 so we shipped
>>> without
>>> > > > it.  There was a JIRA to implement it for later versions,
>>> > > > https://issues.apache.org/jira/browse/KAFKA-5214 , as well as
a
>>> PR,
>>> > > > https://github.com/apache/kafka/pull/3012 .  However, we started
>>> to
>>> > > > rethink whether this AdminClient function was even necessary.
>>> Most of
>>> > > the
>>> > > > use-cases we could think of seemed like horrible hacks.  So it
has
>>> > never
>>> > > > really been implemented (yet?).
>>> > > >
>>> > > > best,
>>> > > > Colin
>>> > > >
>>> > > >
>>> > > > On Tue, Jun 25, 2019, at 15:46, Boyang Chen wrote:
>>> > > > > Actually, after a second thought, I think it actually makes
>>> sense to
>>> > > > > support auto upgrade through admin client to help use get
api
>>> version
>>> > > > > from
>>> > > > > broker.
>>> > > > > A draft KIP is here:
>>> > > > >
>>> > > >
>>> > >
>>> >
>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-483%3A++Add+Broker+Version+API+in+Admin+Client
>>> > > > >
>>> > > > > Boyang
>>> > > > >
>>> > > > > On Tue, Jun 25, 2019 at 2:57 PM Boyang Chen <
>>> > > reluctanthero104@gmail.com>
>>> > > > > wrote:
>>> > > > >
>>> > > > > > Thank you Guozhang, some of my understandings are inline
below.
>>> > > > > >
>>> > > > > > On Tue, Jun 25, 2019 at 11:05 AM Jason Gustafson <
>>> > jason@confluent.io
>>> > > >
>>> > > > > > wrote:
>>> > > > > >
>>> > > > > >> >
>>> > > > > >> > I think co-locating does have some merits here,
i.e.
>>> letting the
>>> > > > > >> > ConsumerCoordinator which has the source-of-truth
of
>>> assignment
>>> > to
>>> > > > act
>>> > > > > >> as
>>> > > > > >> > the TxnCoordinator as well; but I agree there's
also some
>>> cons
>>> > of
>>> > > > > >> coupling
>>> > > > > >> > them together. I'm still a bit inclining towards
colocation
>>> but
>>> > if
>>> > > > there
>>> > > > > >> > are good rationales not to do so I can be convinced
as well.
>>> > > > > >>
>>> > > > > >>
>>> > > > > >> The good rationale is that we have no mechanism
to colocate
>>> > > > partitions ;).
>>> > > > > >> Are you suggesting we store the group and transaction
state
>>> in the
>>> > > > same
>>> > > > > >> log? Can you be more concrete about the benefit?
>>> > > > > >>
>>> > > > > >> -Jason
>>> > > > > >>
>>> > > > > >> On Tue, Jun 25, 2019 at 10:51 AM Guozhang Wang <
>>> > wangguoz@gmail.com>
>>> > > > > >> wrote:
>>> > > > > >>
>>> > > > > >> > Hi Boyang,
>>> > > > > >> >
>>> > > > > >> > 1. One advantage of retry against on-hold is
that it will
>>> not
>>> > > > tie-up a
>>> > > > > >> > handler thread (of course the latter could
do the same but
>>> that
>>> > > > involves
>>> > > > > >> > using a purgatory which is more complicated),
and also it is
>>> > less
>>> > > > > >> likely to
>>> > > > > >> > violate request timeout. So I think there are
some
>>> rationales to
>>> > > > prefer
>>> > > > > >> > retries.
>>> > > > > >> >
>>> > > > > >>
>>> > > > > >  That sounds fair to me, also we are avoiding usage
of another
>>> > > > purgatory
>>> > > > > > instance. Usually for one back-off
>>> > > > > > we are only delaying 50ms during startup which is trivial
cost.
>>> > This
>>> > > > > > behavior shouldn't be changed.
>>> > > > > >
>>> > > > > > > 2. Regarding "ConsumerRebalanceListener": both
>>> > > > ConsumerRebalanceListener
>>> > > > > >> > and PartitionAssignors are user-customizable
modules, and
>>> only
>>> > > > > >> difference
>>> > > > > >> > is that the former is specified via code and
the latter is
>>> > > > specified via
>>> > > > > >> > config.
>>> > > > > >> >
>>> > > > > >> > Regarding Jason's proposal of ConsumerAssignment,
one thing
>>> to
>>> > > note
>>> > > > > >> though
>>> > > > > >> > with KIP-429 the onPartitionAssigned may not
be called if
>>> the
>>> > > > assignment
>>> > > > > >> > does not change, whereas onAssignment would
always be
>>> called at
>>> > > the
>>> > > > end
>>> > > > > >> of
>>> > > > > >> > sync-group response. My proposed semantics
is that
>>> > > > > >> > `RebalanceListener#onPartitionsXXX` are used
for
>>> notifications
>>> > to
>>> > > > user,
>>> > > > > >> and
>>> > > > > >> > hence if there's no changes these will not
be called,
>>> whereas
>>> > > > > >> > `PartitionAssignor` is used for assignor logic,
whose
>>> callback
>>> > > would
>>> > > > > >> always
>>> > > > > >> > be called no matter if the partitions have
changed or not.
>>> > > > > >>
>>> > > > > >> I think a third option is to gracefully expose generation
id
>>> as
>>> > part
>>> > > > of
>>> > > > > > consumer API, so that we don't need to
>>> > > > > > bother overloading various callbacks. Of course, this
builds
>>> upon
>>> > the
>>> > > > > > assumption that topic partitions
>>> > > > > > will not be included in new initTransaction API.
>>> > > > > >
>>> > > > > > > 3. I feel it is a bit awkward to let the TxnCoordinator
>>> keeping
>>> > > > partition
>>> > > > > >> > assignments since it is sort of taking over
the job of the
>>> > > > > >> > ConsumerCoordinator, and may likely cause a
split-brain
>>> problem
>>> > as
>>> > > > two
>>> > > > > >> > coordinators keep a copy of this assignment
which may be
>>> > > different.
>>> > > > > >> >
>>> > > > > >> > I think co-locating does have some merits here,
i.e.
>>> letting the
>>> > > > > >> > ConsumerCoordinator which has the source-of-truth
of
>>> assignment
>>> > to
>>> > > > act
>>> > > > > >> as
>>> > > > > >> > the TxnCoordinator as well; but I agree there's
also some
>>> cons
>>> > of
>>> > > > > >> coupling
>>> > > > > >> > them together. I'm still a bit inclining towards
colocation
>>> but
>>> > if
>>> > > > there
>>> > > > > >> > are good rationales not to do so I can be convinced
as well.
>>> > > > > >> >
>>> > > > > >>
>>> > > > > > The purpose of co-location is to let txn coordinator
see the
>>> group
>>> > > > > > assignment. This priority is weakened
>>> > > > > > when we already have defense on the consumer offset
fetch, so I
>>> > guess
>>> > > > it's
>>> > > > > > not super important anymore.
>>> > > > > >
>>> > > > > >
>>> > > > > >> > 4. I guess I'm preferring the philosophy of
"only add
>>> configs if
>>> > > > > >> there's no
>>> > > > > >> > other ways", since more and more configs would
make it less
>>> and
>>> > > less
>>> > > > > >> > intuitive out of the box to use.
>>> > > > > >> >
>>> > > > > >> > I think it's a valid point that checks upon
starting up
>>> does not
>>> > > > cope
>>> > > > > >> with
>>> > > > > >> > brokers downgrading but even with a config,
but it is still
>>> hard
>>> > > for
>>> > > > > >> users
>>> > > > > >> > to determine when they can be ensured the broker
would never
>>> > > > downgrade
>>> > > > > >> > anymore and hence can safely switch the config.
So my
>>> feeling is
>>> > > > that
>>> > > > > >> this
>>> > > > > >> > config would not be helping too much still.
If we want to
>>> be at
>>> > > the
>>> > > > > >> safer
>>> > > > > >> > side, then I'd suggest we modify the Coordinator
->
>>> > NetworkClient
>>> > > > > >> hierarchy
>>> > > > > >> > to allow the NetworkClient being able to pass
the APIVersion
>>> > > > metadata to
>>> > > > > >> > Coordinator, so that Coordinator can rely on
that logic to
>>> > change
>>> > > > its
>>> > > > > >> > behavior dynamically.
>>> > > > > >>
>>> > > > > > The stream thread init could not be supported by a client
>>> > coordinator
>>> > > > > > behavior change on the fly,
>>> > > > > > we are only losing possibilities after we initialized.
(main
>>> thread
>>> > > > gets
>>> > > > > > exit and no thread has global picture anymore)
>>> > > > > > If we do want to support auto version detection, admin
client
>>> > request
>>> > > > in
>>> > > > > > this sense shall be easier.
>>> > > > > >
>>> > > > > >
>>> > > > > >> >
>>> > > > > >> > 5. I do not have a concrete idea about how
the impact on
>>> Connect
>>> > > > would
>>> > > > > >> > make, maybe Randall or Konstantine can help
here?
>>> > > > > >> >
>>> > > > > >>
>>> > > > > > Sounds good, let's see their thoughts.
>>> > > > > >
>>> > > > > >
>>> > > > > >> > Guozhang
>>> > > > > >> >
>>> > > > > >> > On Mon, Jun 24, 2019 at 10:26 PM Boyang Chen
<
>>> > > > > >> reluctanthero104@gmail.com>
>>> > > > > >> > wrote:
>>> > > > > >> >
>>> > > > > >> > > Hey Jason,
>>> > > > > >> > >
>>> > > > > >> > > thank you for the proposal here. Some
of my thoughts
>>> below.
>>> > > > > >> > >
>>> > > > > >> > > On Mon, Jun 24, 2019 at 8:58 PM Jason
Gustafson <
>>> > > > jason@confluent.io>
>>> > > > > >> > > wrote:
>>> > > > > >> > >
>>> > > > > >> > > > Hi Boyang,
>>> > > > > >> > > >
>>> > > > > >> > > > Thanks for picking this up! Still
reading through the
>>> > updates,
>>> > > > but
>>> > > > > >> here
>>> > > > > >> > > are
>>> > > > > >> > > > a couple initial comments on the
APIs:
>>> > > > > >> > > >
>>> > > > > >> > > > 1. The `TxnProducerIdentity` class
is a bit awkward. I
>>> think
>>> > > we
>>> > > > are
>>> > > > > >> > > trying
>>> > > > > >> > > > to encapsulate state from the current
group assignment.
>>> > Maybe
>>> > > > > >> something
>>> > > > > >> > > > like `ConsumerAssignment` would be
clearer? If we make
>>> the
>>> > > usage
>>> > > > > >> > > consistent
>>> > > > > >> > > > across the consumer and producer,
then we can avoid
>>> exposing
>>> > > > > >> internal
>>> > > > > >> > > state
>>> > > > > >> > > > like the generationId.
>>> > > > > >> > > >
>>> > > > > >> > > > For example:
>>> > > > > >> > > >
>>> > > > > >> > > > // Public API
>>> > > > > >> > > > interface ConsumerAssignment {
>>> > > > > >> > > >   Set<TopicPartition> partittions();
>>> > > > > >> > > > }
>>> > > > > >> > > >
>>> > > > > >> > > > // Not a public API
>>> > > > > >> > > > class InternalConsumerAssignment
implements
>>> > > ConsumerAssignment {
>>> > > > > >> > > >   Set<TopicPartition> partittions;
>>> > > > > >> > > >   int generationId;
>>> > > > > >> > > > }
>>> > > > > >> > > >
>>> > > > > >> > > > Then we can change the rebalance
listener to something
>>> like
>>> > > > this:
>>> > > > > >> > > > onPartitionsAssigned(ConsumerAssignment
assignment)
>>> > > > > >> > > >
>>> > > > > >> > > > And on the producer:
>>> > > > > >> > > > void initTransactions(String groupId,
ConsumerAssignment
>>> > > > > >> assignment);
>>> > > > > >> > > >
>>> > > > > >> > > > 2. Another bit of awkwardness is
the fact that we have
>>> to
>>> > pass
>>> > > > the
>>> > > > > >> > > groupId
>>> > > > > >> > > > through both initTransactions() and
>>> > > sendOffsetsToTransaction().
>>> > > > We
>>> > > > > >> > could
>>> > > > > >> > > > consider a config instead. Maybe
something like `
>>> > > > > >> > transactional.group.id
>>> > > > > >> > > `?
>>> > > > > >> > > > Then we could simplify the producer
APIs, potentially
>>> even
>>> > > > > >> deprecating
>>> > > > > >> > > the
>>> > > > > >> > > > current sendOffsetsToTransaction.
In fact, for this new
>>> > usage,
>>> > > > the `
>>> > > > > >> > > > transational.id` config is not needed.
It would be
>>> nice if
>>> > we
>>> > > > don't
>>> > > > > >> > have
>>> > > > > >> > > > to
>>> > > > > >> > > > provide it.
>>> > > > > >> > > >
>>> > > > > >> > > > I like the idea of combining 1 and
2. We could
>>> definitely
>>> > pass
>>> > > > in a
>>> > > > > >> > > group.id config
>>> > > > > >> > > so that we could avoid exposing that information
in a
>>> public
>>> > > API.
>>> > > > The
>>> > > > > >> > > question I have
>>> > > > > >> > > is that whether we should name the interface
>>> `GroupAssignment`
>>> > > > > >> instead,
>>> > > > > >> > so
>>> > > > > >> > > that Connect later
>>> > > > > >> > > could also extend on the same interface,
just to echo
>>> > Guozhang's
>>> > > > point
>>> > > > > >> > > here, Also the base interface
>>> > > > > >> > > is better to be defined empty for easy
extension, or
>>> define an
>>> > > > > >> abstract
>>> > > > > >> > > type called `Resource` to be shareable
>>> > > > > >> > > later IMHO.
>>> > > > > >> > >
>>> > > > > >> > >
>>> > > > > >> > > > By the way, I'm a bit confused about
discussion above
>>> about
>>> > > > > >> colocating
>>> > > > > >> > > the
>>> > > > > >> > > > txn and group coordinators. That
is not actually
>>> necessary,
>>> > is
>>> > > > it?
>>> > > > > >> > > >
>>> > > > > >> > > > Yes, this is not a requirement for
this KIP, because it
>>> is
>>> > > > > >> inherently
>>> > > > > >> > > impossible to
>>> > > > > >> > > achieve co-locating  topic partition of
transaction log
>>> and
>>> > > > consumed
>>> > > > > >> > offset
>>> > > > > >> > > topics.
>>> > > > > >> > >
>>> > > > > >> > >
>>> > > > > >> > > > Thanks,
>>> > > > > >> > > > Jason
>>> > > > > >> > > >
>>> > > > > >> > > On Mon, Jun 24, 2019 at 10:07 AM Boyang
Chen <
>>> > > > > >> reluctanthero104@gmail.com
>>> > > > > >> > >
>>> > > > > >> > > > wrote:
>>> > > > > >> > > >
>>> > > > > >> > > > > Thank you Ismael for the suggestion.
We will attempt
>>> to
>>> > > > address
>>> > > > > >> it by
>>> > > > > >> > > > > giving more details to rejected
alternative section.
>>> > > > > >> > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > > > Thank you for the comment Guozhang!
Answers are inline
>>> > > below.
>>> > > > > >> > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > > > On Sun, Jun 23, 2019 at 6:33
PM Guozhang Wang <
>>> > > > wangguoz@gmail.com
>>> > > > > >> >
>>> > > > > >> > > > wrote:
>>> > > > > >> > > > >
>>> > > > > >> > > > > > Hello Boyang,
>>> > > > > >> > > > > >
>>> > > > > >> > > > > > Thanks for the KIP, I have
some comments below:
>>> > > > > >> > > > > >
>>> > > > > >> > > > > > 1. "Once transactions are
complete, the call will
>>> > return."
>>> > > > This
>>> > > > > >> > seems
>>> > > > > >> > > > > > different from the existing
behavior, in which we
>>> would
>>> > > > return a
>>> > > > > >> > > > > retriable
>>> > > > > >> > > > > > CONCURRENT_TRANSACTIONS
and let the client to
>>> retry, is
>>> > > this
>>> > > > > >> > > > intentional?
>>> > > > > >> > > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > > > I don’t think it is intentional,
and I will defer this
>>> > > > question to
>>> > > > > >> > > Jason
>>> > > > > >> > > > > when he got time to answer since
from what I
>>> understood
>>> > > retry
>>> > > > and
>>> > > > > >> on
>>> > > > > >> > > hold
>>> > > > > >> > > > > seem both valid approaches.
>>> > > > > >> > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > > > > 2. "an overload to onPartitionsAssigned
in the
>>> > consumer's
>>> > > > > >> rebalance
>>> > > > > >> > > > > > listener interface": as
part of KIP-341 we've
>>> already
>>> > add
>>> > > > this
>>> > > > > >> > > > > information
>>> > > > > >> > > > > > to the onAssignment callback.
Would this be
>>> sufficient?
>>> > Or
>>> > > > more
>>> > > > > >> > > > generally
>>> > > > > >> > > > > > speaking, which information
have to be passed
>>> around in
>>> > > > > >> rebalance
>>> > > > > >> > > > > callback
>>> > > > > >> > > > > > while others can be passed
around in
>>> PartitionAssignor
>>> > > > > >> callback? In
>>> > > > > >> > > > > Streams
>>> > > > > >> > > > > > for example both callbacks
are used but most
>>> critical
>>> > > > > >> information
>>> > > > > >> > is
>>> > > > > >> > > > > passed
>>> > > > > >> > > > > > via onAssignment.
>>> > > > > >> > > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > > > We still need to extend ConsumerRebalanceListener
>>> because
>>> > > > it’s the
>>> > > > > >> > > > > interface we could have public
access to. The
>>> > #onAssignment
>>> > > > call
>>> > > > > >> is
>>> > > > > >> > > > defined
>>> > > > > >> > > > > on PartitionAssignor level which
is not easy to work
>>> with
>>> > > > external
>>> > > > > >> > > > > producers.
>>> > > > > >> > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > > > > 3. "We propose to use a
separate record type in
>>> order to
>>> > > > store
>>> > > > > >> the
>>> > > > > >> > > > group
>>> > > > > >> > > > > > assignment.": hmm, I thought
with the third typed
>>> > > > > >> FindCoordinator,
>>> > > > > >> > > the
>>> > > > > >> > > > > same
>>> > > > > >> > > > > > broker that act as the
 consumer coordinator would
>>> > always
>>> > > be
>>> > > > > >> > selected
>>> > > > > >> > > > as
>>> > > > > >> > > > > > the txn coordinator, in
which case it can access its
>>> > local
>>> > > > cache
>>> > > > > >> > > > > metadata /
>>> > > > > >> > > > > > offset topic to get this
information already? We
>>> just
>>> > need
>>> > > > to
>>> > > > > >> think
>>> > > > > >> > > > about
>>> > > > > >> > > > > > how to make these two modules
directly exchange
>>> > > information
>>> > > > > >> without
>>> > > > > >> > > > > messing
>>> > > > > >> > > > > > up the code hierarchy.
>>> > > > > >> > > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > > > These two coordinators will
be on the same broker only
>>> > when
>>> > > > > >> number of
>>> > > > > >> > > > > partitions for transaction state
topic and consumer
>>> offset
>>> > > > topic
>>> > > > > >> are
>>> > > > > >> > > the
>>> > > > > >> > > > > same. This normally holds true,
but I'm afraid
>>> > > > > >> > > > > we couldn't make this assumption?
>>> > > > > >> > > > >
>>> > > > > >> > > > > 4. The config of "CONSUMER_GROUP_AWARE_TRANSACTION":
>>> it
>>> > > seems
>>> > > > the
>>> > > > > >> > goal
>>> > > > > >> > > of
>>> > > > > >> > > > > > this config is just to
avoid old-versioned broker
>>> to not
>>> > > be
>>> > > > > >> able to
>>> > > > > >> > > > > > recognize newer versioned
client. I think if we can
>>> do
>>> > > > something
>>> > > > > >> > else
>>> > > > > >> > > > to
>>> > > > > >> > > > > > avoid this config though,
for example we can use the
>>> > > > embedded
>>> > > > > >> > > > AdminClient
>>> > > > > >> > > > > > to send the APIVersion
request upon starting up, and
>>> > based
>>> > > > on
>>> > > > > >> the
>>> > > > > >> > > > > returned
>>> > > > > >> > > > > > value decides whether to
go to the old code path or
>>> the
>>> > > new
>>> > > > > >> > behavior.
>>> > > > > >> > > > > > Admittedly asking a random
broker about APIVersion
>>> does
>>> > > not
>>> > > > > >> > guarantee
>>> > > > > >> > > > the
>>> > > > > >> > > > > > whole cluster's versions,
but what we can do is to
>>> first
>>> > > 1)
>>> > > > find
>>> > > > > >> > the
>>> > > > > >> > > > > > coordinator (and if the
random broker does not even
>>> > > > recognize
>>> > > > > >> the
>>> > > > > >> > new
>>> > > > > >> > > > > > discover type, fall back
to old path directly), and
>>> then
>>> > > 2)
>>> > > > ask
>>> > > > > >> the
>>> > > > > >> > > > > > discovered coordinator
about its supported
>>> APIVersion.
>>> > > > > >> > > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > > > The caveat here is that we have
to make sure both the
>>> > group
>>> > > > > >> > coordinator
>>> > > > > >> > > > and
>>> > > > > >> > > > > transaction coordinator are
on the latest version
>>> during
>>> > > init
>>> > > > > >> stage.
>>> > > > > >> > > This
>>> > > > > >> > > > > is potentially doable as we
only need a consumer
>>> group.id
>>> > > > > >> > > > > to check that. In the meantime,
a hard-coded config is
>>> > > still a
>>> > > > > >> > > favorable
>>> > > > > >> > > > > backup in case the server has
downgraded, so you will
>>> want
>>> > > to
>>> > > > use
>>> > > > > >> a
>>> > > > > >> > new
>>> > > > > >> > > > > version client without `consumer
group` transactional
>>> > > support.
>>> > > > > >> > > > >
>>> > > > > >> > > > > 5. This is a meta question:
have you considered how
>>> this
>>> > can
>>> > > > be
>>> > > > > >> > applied
>>> > > > > >> > > > to
>>> > > > > >> > > > > > Kafka Connect as well?
For example, for source
>>> > connectors,
>>> > > > the
>>> > > > > >> > > > assignment
>>> > > > > >> > > > > > is not by "partitions",
but by some other sort of
>>> > > > "resources"
>>> > > > > >> based
>>> > > > > >> > > on
>>> > > > > >> > > > > the
>>> > > > > >> > > > > > source systems, how KIP-447
would affect Kafka
>>> > Connectors
>>> > > > that
>>> > > > > >> > > > > implemented
>>> > > > > >> > > > > > EOS as well?
>>> > > > > >> > > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > > > No, it's not currently included
in the scope. Could
>>> you
>>> > > point
>>> > > > me
>>> > > > > >> to a
>>> > > > > >> > > > > sample source connector who
uses EOS? Could always
>>> > > piggy-back
>>> > > > into
>>> > > > > >> > the
>>> > > > > >> > > > > TxnProducerIdentity struct with
more information such
>>> as
>>> > > > tasks. If
>>> > > > > >> > > > > this is something to support
in near term, an abstract
>>> > type
>>> > > > called
>>> > > > > >> > > > > "Resource" could be provided
and let topic partition
>>> and
>>> > > > connect
>>> > > > > >> task
>>> > > > > >> > > > > implement it.
>>> > > > > >> > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > > > >
>>> > > > > >> > > > > > Guozhang
>>> > > > > >> > > > > >
>>> > > > > >> > > > > >
>>> > > > > >> > > > > > On Sat, Jun 22, 2019 at
8:40 PM Ismael Juma <
>>> > > > ismael@juma.me.uk>
>>> > > > > >> > > wrote:
>>> > > > > >> > > > > >
>>> > > > > >> > > > > > > Hi Boyang,
>>> > > > > >> > > > > > >
>>> > > > > >> > > > > > > Thanks for the KIP.
It's good that we listed a
>>> number
>>> > of
>>> > > > > >> rejected
>>> > > > > >> > > > > > > alternatives. It would
be helpful to have an
>>> > explanation
>>> > > > of
>>> > > > > >> why
>>> > > > > >> > > they
>>> > > > > >> > > > > were
>>> > > > > >> > > > > > > rejected.
>>> > > > > >> > > > > > >
>>> > > > > >> > > > > > > Ismael
>>> > > > > >> > > > > > >
>>> > > > > >> > > > > > > On Sat, Jun 22, 2019
at 8:31 PM Boyang Chen <
>>> > > > > >> bchen11@outlook.com
>>> > > > > >> > >
>>> > > > > >> > > > > wrote:
>>> > > > > >> > > > > > >
>>> > > > > >> > > > > > > > Hey all,
>>> > > > > >> > > > > > > >
>>> > > > > >> > > > > > > > I would like
to start a discussion for KIP-447:
>>> > > > > >> > > > > > > >
>>> > > > > >> > > > > > > >
>>> > > > > >> > > > > > >
>>> > > > > >> > > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > >
>>> > > > > >> > >
>>> > > > > >> >
>>> > > > > >>
>>> > > >
>>> > >
>>> >
>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-447%3A+Producer+scalability+for+exactly+once+semantics
>>> > > > > >> > > > > > > >
>>> > > > > >> > > > > > > > this is a work
originated by Jason Gustafson
>>> and we
>>> > > > would
>>> > > > > >> like
>>> > > > > >> > to
>>> > > > > >> > > > > > proceed
>>> > > > > >> > > > > > > > into discussion
stage.
>>> > > > > >> > > > > > > >
>>> > > > > >> > > > > > > > Let me know your
thoughts, thanks!
>>> > > > > >> > > > > > > >
>>> > > > > >> > > > > > > > Boyang
>>> > > > > >> > > > > > > >
>>> > > > > >> > > > > > >
>>> > > > > >> > > > > >
>>> > > > > >> > > > > >
>>> > > > > >> > > > > > --
>>> > > > > >> > > > > > -- Guozhang
>>> > > > > >> > > > > >
>>> > > > > >> > > > >
>>> > > > > >> > > >
>>> > > > > >> > >
>>> > > > > >> >
>>> > > > > >> >
>>> > > > > >> > --
>>> > > > > >> > -- Guozhang
>>> > > > > >> >
>>> > > > > >>
>>> > > > > >
>>> > > > >
>>> > > >
>>> > >
>>> >
>>>
>>>
>>> --
>>> -- Guozhang
>>>
>>

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