Hey Jun,
Do you think the current KIP looks OK? I am wondering if we can open the
voting thread.
Thanks!
Dong
On Fri, Jan 19, 2018 at 3:08 PM, Dong Lin <lindon...@gmail.com> wrote:
> Hey Jun,
>
> I think we can probably have a static method in Util class to decode the
> byte[]. Both KafkaConsumer implementation and the user application will be
> able to decode the byte array and log its content for debug purpose. So it
> seems that we can still print the information we want. It is just not
> explicitly exposed in the consumer interface. Would this address the
> problem here?
>
> Yeah we can include OffsetEpoch in AdminClient. This can be added in
> KIP-222? Is there something you would like me to add in this KIP?
>
> Thanks!
> Dong
>
> On Fri, Jan 19, 2018 at 3:00 PM, Jun Rao <j...@confluent.io> wrote:
>
>> Hi, Dong,
>>
>> The issue with using just byte[] for OffsetEpoch is that it won't be
>> printable, which makes debugging harder.
>>
>> Also, KIP-222 proposes a listGroupOffset() method in AdminClient. If that
>> gets adopted before this KIP, we probably want to include OffsetEpoch in
>> the AdminClient too.
>>
>> Thanks,
>>
>> Jun
>>
>>
>> On Thu, Jan 18, 2018 at 6:30 PM, Dong Lin <lindon...@gmail.com> wrote:
>>
>> > Hey Jun,
>> >
>> > I agree. I have updated the KIP to remove the class OffetEpoch and
>> replace
>> > OffsetEpoch with byte[] in APIs that use it. Can you see if it looks
>> good?
>> >
>> > Thanks!
>> > Dong
>> >
>> > On Thu, Jan 18, 2018 at 6:07 PM, Jun Rao <j...@confluent.io> wrote:
>> >
>> > > Hi, Dong,
>> > >
>> > > Thanks for the updated KIP. It looks good to me now. The only thing is
>> > > for OffsetEpoch.
>> > > If we expose the individual fields in the class, we probably don't
>> need
>> > the
>> > > encode/decode methods. If we want to hide the details of OffsetEpoch,
>> we
>> > > probably don't want expose the individual fields.
>> > >
>> > > Jun
>> > >
>> > > On Wed, Jan 17, 2018 at 10:10 AM, Dong Lin <lindon...@gmail.com>
>> wrote:
>> > >
>> > > > Thinking about point 61 more, I realize that the async zookeeper
>> read
>> > may
>> > > > make it less of an issue for controller to read more zookeeper
>> nodes.
>> > > > Writing partition_epoch in the per-partition znode makes it simpler
>> to
>> > > > handle the broker failure between zookeeper writes for a topic
>> > creation.
>> > > I
>> > > > have updated the KIP to use the suggested approach.
>> > > >
>> > > >
>> > > > On Wed, Jan 17, 2018 at 9:57 AM, Dong Lin <lindon...@gmail.com>
>> wrote:
>> > > >
>> > > > > Hey Jun,
>> > > > >
>> > > > > Thanks much for the comments. Please see my comments inline.
>> > > > >
>> > > > > On Tue, Jan 16, 2018 at 4:38 PM, Jun Rao <j...@confluent.io>
>> wrote:
>> > > > >
>> > > > >> Hi, Dong,
>> > > > >>
>> > > > >> Thanks for the updated KIP. Looks good to me overall. Just a few
>> > minor
>> > > > >> comments.
>> > > > >>
>> > > > >> 60. OffsetAndMetadata positionAndOffsetEpoch(TopicPartition
>> > > partition):
>> > > > >> It
>> > > > >> seems that there is no need to return metadata. We probably want
>> to
>> > > > return
>> > > > >> sth like OffsetAndEpoch.
>> > > > >>
>> > > > >
>> > > > > Previously I think we may want to re-use the existing class to
>> keep
>> > our
>> > > > > consumer interface simpler. I have updated the KIP to add class
>> > > > > OffsetAndOffsetEpoch. I didn't use OffsetAndEpoch because user may
>> > > > confuse
>> > > > > this name with OffsetEpoch. Does this sound OK?
>> > > > >
>> > > > >
>> > > > >>
>> > > > >> 61. Should we store partition_epoch in
>> > > > >> /brokers/topics/[topic]/partitions/[partitionId] in ZK?
>> > > > >>
>> > > > >
>> > > > > I have considered this. I think the advantage of adding the
>> > > > > partition->partition_epoch map in the existing
>> > > > > znode /brokers/topics/[topic]/partitions is that controller only
>> > needs
>> > > > to
>> > > > > read one znode per topic to gets its partition_epoch information.
>> > > > Otherwise
>> > > > > controller may need to read one extra znode per partition to get
>> the
>> > > same
>> > > > > information.
>> > > > >
>> > > > > When we delete partition or expand partition of a topic, someone
>> > needs
>> > > to
>> > > > > modify partition->partition_epoch map in znode
>> > > > > /brokers/topics/[topic]/partitions. This may seem a bit more
>> > > complicated
>> > > > > than simply adding or deleting znode /brokers/topics/[topic]/
>> > > > partitions/[partitionId].
>> > > > > But the complexity is probably similar to the existing operation
>> of
>> > > > > modifying the partition->replica_list mapping in znode
>> > > > > /brokers/topics/[topic]. So not sure it is better to store the
>> > > > > partition_epoch in /brokers/topics/[topic]/partit
>> ions/[partitionId].
>> > > > What
>> > > > > do you think?
>> > > > >
>> > > > >
>> > > > >>
>> > > > >> 62. For checking outdated metadata in the client, we probably
>> want
>> > to
>> > > > add
>> > > > >> when max_partition_epoch will be used.
>> > > > >>
>> > > > >
>> > > > > The max_partition_epoch is used in the Proposed Changes ->
>> Client's
>> > > > > metadata refresh section to determine whether a metadata is
>> outdated.
>> > > And
>> > > > > this formula is referenced and re-used in other sections to
>> determine
>> > > > > whether a metadata is outdated. Does this formula look OK?
>> > > > >
>> > > > >
>> > > > >>
>> > > > >> 63. "The leader_epoch should be the largest leader_epoch of
>> messages
>> > > > whose
>> > > > >> offset < the commit offset. If no message has been consumed since
>> > > > consumer
>> > > > >> initialization, the leader_epoch from seek(...) or
>> > OffsetFetchResponse
>> > > > >> should be used. The partition_epoch should be read from the last
>> > > > >> FetchResponse corresponding to the given partition and commit
>> > offset.
>> > > ":
>> > > > >> leader_epoch and partition_epoch are associated with an offset.
>> So,
>> > if
>> > > > no
>> > > > >> message is consumed, there is no offset and therefore there is no
>> > need
>> > > > to
>> > > > >> read leader_epoch and partition_epoch. Also, the leader_epoch
>> > > associated
>> > > > >> with the offset should just come from the messages returned in
>> the
>> > > fetch
>> > > > >> response.
>> > > > >>
>> > > > >
>> > > > > I am thinking that, if user calls seek(..) and commitSync(...)
>> > without
>> > > > > consuming any messages, we should re-use the leader_epoch and
>> > > > > partition_epoch provided by the seek(...) in the
>> OffsetCommitRequest.
>> > > And
>> > > > > if messages have been successfully consumed, then leader_epoch
>> will
>> > > come
>> > > > > from the messages returned in the fetch response. The condition
>> > > "messages
>> > > > > whose offset < the commit offset" is needed to take care of the
>> log
>> > > > > compacted topic which may have offset gap due to log cleaning.
>> > > > >
>> > > > > Did I miss something here? Or should I rephrase the paragraph to
>> make
>> > > it
>> > > > > less confusing?
>> > > > >
>> > > > >
>> > > > >> 64. Could you include the public methods in the OffsetEpoch
>> class?
>> > > > >>
>> > > > >
>> > > > > I mistakenly deleted the definition of OffsetEpoch class from the
>> > KIP.
>> > > I
>> > > > > just added it back with the public methods. Could you take another
>> > > look?
>> > > > >
>> > > > >
>> > > > >>
>> > > > >> Jun
>> > > > >>
>> > > > >>
>> > > > >> On Thu, Jan 11, 2018 at 5:43 PM, Dong Lin <lindon...@gmail.com>
>> > > wrote:
>> > > > >>
>> > > > >> > Hey Jun,
>> > > > >> >
>> > > > >> > Thanks much. I agree that we can not rely on committed offsets
>> to
>> > be
>> > > > >> always
>> > > > >> > deleted when we delete topic. So it is necessary to use a
>> > > > per-partition
>> > > > >> > epoch that does not change unless this partition is deleted. I
>> > also
>> > > > >> agree
>> > > > >> > that it is very nice to be able to uniquely identify a message
>> > with
>> > > > >> > (offset, leader_epoch, partition_epoch) in face of potential
>> topic
>> > > > >> deletion
>> > > > >> > and unclean leader election.
>> > > > >> >
>> > > > >> > I agree with all your comments. And I have updated the KIP
>> based
>> > on
>> > > > our
>> > > > >> > latest discussion. In addition, I added
>> > > InvalidPartitionEpochException
>> > > > >> > which will be thrown by consumer.poll() if the partition_epoch
>> > > > >> associated
>> > > > >> > with the partition, which can be given to consumer using
>> > seek(...),
>> > > is
>> > > > >> > different from the partition_epoch in the FetchResponse.
>> > > > >> >
>> > > > >> > Can you take another look at the latest KIP?
>> > > > >> >
>> > > > >> > Thanks!
>> > > > >> > Dong
>> > > > >> >
>> > > > >> >
>> > > > >> >
>> > > > >> > On Wed, Jan 10, 2018 at 2:24 PM, Jun Rao <j...@confluent.io>
>> > wrote:
>> > > > >> >
>> > > > >> > > Hi, Dong,
>> > > > >> > >
>> > > > >> > > My replies are the following.
>> > > > >> > >
>> > > > >> > > 60. What you described could also work. The drawback is that
>> we
>> > > will
>> > > > >> be
>> > > > >> > > unnecessarily changing the partition epoch when a partition
>> > hasn't
>> > > > >> really
>> > > > >> > > changed. I was imagining that the partition epoch will be
>> stored
>> > > in
>> > > > >> > > /brokers/topics/[topic]/partitions/[partitionId], instead
>> of at
>> > > the
>> > > > >> > topic
>> > > > >> > > level. So, not sure if ZK size limit is an issue.
>> > > > >> > >
>> > > > >> > > 61, 62 and 65. To me, the offset + offset_epoch is a unique
>> > > > identifier
>> > > > >> > for
>> > > > >> > > a message. So, if a message hasn't changed, the offset and
>> the
>> > > > >> associated
>> > > > >> > > offset_epoch ideally should remain the same (it will be kind
>> of
>> > > > weird
>> > > > >> if
>> > > > >> > > two consumer apps save the offset on the same message, but
>> the
>> > > > >> > offset_epoch
>> > > > >> > > are different). partition_epoch + leader_epoch give us that.
>> > > > >> > global_epoch +
>> > > > >> > > leader_epoch don't. If we use this approach, we can solve not
>> > only
>> > > > the
>> > > > >> > > problem that you have identified, but also other problems
>> when
>> > > there
>> > > > >> is
>> > > > >> > > data loss or topic re-creation more reliably. For example, in
>> > the
>> > > > >> future,
>> > > > >> > > if we include the partition_epoch and leader_epoch in the
>> fetch
>> > > > >> request,
>> > > > >> > > the server can do a more reliable check of whether that
>> offset
>> > is
>> > > > >> valid
>> > > > >> > or
>> > > > >> > > not. I am not sure that we can rely upon all external
>> offsets to
>> > > be
>> > > > >> > removed
>> > > > >> > > on topic deletion. For example, a topic may be deleted by an
>> > admin
>> > > > who
>> > > > >> > may
>> > > > >> > > not know all the applications.
>> > > > >> > >
>> > > > >> > > If we agree on the above, the second question is then how to
>> > > > reliably
>> > > > >> > > propagate the partition_epoch and the leader_epoch to the
>> > consumer
>> > > > >> when
>> > > > >> > > there are leader or partition changes. The leader_epoch comes
>> > from
>> > > > the
>> > > > >> > > message, which is reliable. So, I was suggesting that when we
>> > > store
>> > > > an
>> > > > >> > > offset, we can just store the leader_epoch from the message
>> set
>> > > > >> > containing
>> > > > >> > > that offset. Similarly, I was thinking that if the
>> > partition_epoch
>> > > > is
>> > > > >> in
>> > > > >> > > the fetch response, we can propagate partition_epoch reliably
>> > > where
>> > > > is
>> > > > >> > > partition_epoch change.
>> > > > >> > >
>> > > > >> > > 63. My point is that once a leader is producing a message in
>> the
>> > > new
>> > > > >> > > partition_epoch, ideally, we should associate the new offsets
>> > with
>> > > > the
>> > > > >> > new
>> > > > >> > > partition_epoch. Otherwise, the offset_epoch won't be the
>> > correct
>> > > > >> unique
>> > > > >> > > identifier (useful for solving other problems mentioned
>> above).
>> > I
>> > > > was
>> > > > >> > > originally thinking that the leader will include the
>> > > partition_epoch
>> > > > >> in
>> > > > >> > the
>> > > > >> > > metadata cache in the fetch response. It's just that right
>> now,
>> > > > >> metadata
>> > > > >> > > cache is updated on UpdateMetadataRequest, which typically
>> > happens
>> > > > >> after
>> > > > >> > > the LeaderAndIsrRequest. Another approach is for the leader
>> to
>> > > cache
>> > > > >> the
>> > > > >> > > partition_epoch in the Partition object and return that
>> (instead
>> > > of
>> > > > >> the
>> > > > >> > one
>> > > > >> > > in metadata cache) in the fetch response.
>> > > > >> > >
>> > > > >> > > 65. It seems to me that the global_epoch and the
>> partition_epoch
>> > > > have
>> > > > >> > > different purposes. A partition_epoch has the benefit that it
>> > (1)
>> > > > can
>> > > > >> be
>> > > > >> > > used to form a unique identifier for a message and (2) can be
>> > used
>> > > > to
>> > > > >> > > solve other
>> > > > >> > > corner case problems in the future. I am not sure having
>> just a
>> > > > >> > > global_epoch can achieve these. global_epoch is useful to
>> > > determine
>> > > > >> which
>> > > > >> > > version of the metadata is newer, especially with topic
>> > deletion.
>> > > > >> > >
>> > > > >> > > Thanks,
>> > > > >> > >
>> > > > >> > > Jun
>> > > > >> > >
>> > > > >> > > On Tue, Jan 9, 2018 at 11:34 PM, Dong Lin <
>> lindon...@gmail.com>
>> > > > >> wrote:
>> > > > >> > >
>> > > > >> > > > Regarding the use of the global epoch in 65), it is very
>> > similar
>> > > > to
>> > > > >> the
>> > > > >> > > > proposal of the metadata_epoch we discussed earlier. The
>> main
>> > > > >> > difference
>> > > > >> > > is
>> > > > >> > > > that this epoch is incremented when we create/expand/delete
>> > > topic
>> > > > >> and
>> > > > >> > > does
>> > > > >> > > > not change when controller re-send metadata.
>> > > > >> > > >
>> > > > >> > > > I looked at our previous discussion. It seems that we
>> prefer
>> > > > >> > > > partition_epoch over the metadata_epoch because 1) we
>> prefer
>> > not
>> > > > to
>> > > > >> > have
>> > > > >> > > an
>> > > > >> > > > ever growing metadata_epoch and 2) we can reset offset
>> better
>> > > when
>> > > > >> > topic
>> > > > >> > > is
>> > > > >> > > > re-created. The use of global topic_epoch avoids the
>> drawback
>> > of
>> > > > an
>> > > > >> > ever
>> > > > >> > > > quickly ever growing metadata_epoch. Though the global
>> epoch
>> > > does
>> > > > >> not
>> > > > >> > > allow
>> > > > >> > > > us to recognize the invalid offset committed before the
>> topic
>> > > > >> > > re-creation,
>> > > > >> > > > we can probably just delete the offset when we delete a
>> topic.
>> > > > Thus
>> > > > >> I
>> > > > >> > am
>> > > > >> > > > not very sure whether it is still worthwhile to have a
>> > > > per-partition
>> > > > >> > > > partition_epoch if the metadata already has the global
>> epoch.
>> > > > >> > > >
>> > > > >> > > >
>> > > > >> > > > On Tue, Jan 9, 2018 at 6:58 PM, Dong Lin <
>> lindon...@gmail.com
>> > >
>> > > > >> wrote:
>> > > > >> > > >
>> > > > >> > > > > Hey Jun,
>> > > > >> > > > >
>> > > > >> > > > > Thanks so much. These comments very useful. Please see
>> below
>> > > my
>> > > > >> > > comments.
>> > > > >> > > > >
>> > > > >> > > > > On Mon, Jan 8, 2018 at 5:52 PM, Jun Rao <
>> j...@confluent.io>
>> > > > wrote:
>> > > > >> > > > >
>> > > > >> > > > >> Hi, Dong,
>> > > > >> > > > >>
>> > > > >> > > > >> Thanks for the updated KIP. A few more comments.
>> > > > >> > > > >>
>> > > > >> > > > >> 60. Perhaps having a partition epoch is more flexible
>> since
>> > > in
>> > > > >> the
>> > > > >> > > > future,
>> > > > >> > > > >> we may support deleting a partition as well.
>> > > > >> > > > >>
>> > > > >> > > > >
>> > > > >> > > > > Yeah I have considered this. I think we can probably
>> still
>> > > > support
>> > > > >> > > > > deleting a partition by using the topic_epoch -- when
>> > > partition
>> > > > >> of a
>> > > > >> > > > topic
>> > > > >> > > > > is deleted or created, epoch of all partitions of this
>> topic
>> > > > will
>> > > > >> be
>> > > > >> > > > > incremented by 1. Therefore, if that partition is
>> re-created
>> > > > >> later,
>> > > > >> > the
>> > > > >> > > > > epoch of that partition will still be larger than its
>> epoch
>> > > > before
>> > > > >> > the
>> > > > >> > > > > deletion, which still allows the client to order the
>> > metadata
>> > > > for
>> > > > >> the
>> > > > >> > > > > purpose of this KIP. Does this sound reasonable?
>> > > > >> > > > >
>> > > > >> > > > > The advantage of using topic_epoch instead of
>> > partition_epoch
>> > > is
>> > > > >> that
>> > > > >> > > the
>> > > > >> > > > > size of the /brokers/topics/[topic] znode and
>> > request/response
>> > > > >> size
>> > > > >> > can
>> > > > >> > > > be
>> > > > >> > > > > smaller. We have a limit on the maximum size of znode
>> > > (typically
>> > > > >> > 1MB).
>> > > > >> > > > Use
>> > > > >> > > > > partition epoch can effectively reduce the number of
>> > > partitions
>> > > > >> that
>> > > > >> > > can
>> > > > >> > > > be
>> > > > >> > > > > described by the /brokers/topics/[topic] znode.
>> > > > >> > > > >
>> > > > >> > > > > One use-case of partition_epoch for client to detect that
>> > the
>> > > > >> > committed
>> > > > >> > > > > offset, either from kafka offset topic or from the
>> external
>> > > > store
>> > > > >> is
>> > > > >> > > > > invalid after partition deletion and re-creation.
>> However,
>> > it
>> > > > >> seems
>> > > > >> > > that
>> > > > >> > > > we
>> > > > >> > > > > can also address this use-case with other approaches. For
>> > > > example,
>> > > > >> > when
>> > > > >> > > > > AdminClient deletes partitions, it can also delete the
>> > > committed
>> > > > >> > > offsets
>> > > > >> > > > > for those partitions from the offset topic. If user
>> stores
>> > > > offset
>> > > > >> > > > > externally, it might make sense for user to similarly
>> remove
>> > > > >> offsets
>> > > > >> > of
>> > > > >> > > > > related partitions after these partitions are deleted.
>> So I
>> > am
>> > > > not
>> > > > >> > sure
>> > > > >> > > > > that we should use partition_epoch in this KIP.
>> > > > >> > > > >
>> > > > >> > > > >
>> > > > >> > > > >>
>> > > > >> > > > >> 61. It seems that the leader epoch returned in the
>> > position()
>> > > > >> call
>> > > > >> > > > should
>> > > > >> > > > >> the the leader epoch returned in the fetch response, not
>> > the
>> > > > one
>> > > > >> in
>> > > > >> > > the
>> > > > >> > > > >> metadata cache of the client.
>> > > > >> > > > >
>> > > > >> > > > >
>> > > > >> > > > > I think this is a good idea. Just to double check, this
>> > change
>> > > > >> does
>> > > > >> > not
>> > > > >> > > > > affect the correctness or performance of this KIP. But it
>> > can
>> > > be
>> > > > >> > useful
>> > > > >> > > > if
>> > > > >> > > > > we want to use the leader_epoch to better handle the
>> offset
>> > > rest
>> > > > >> in
>> > > > >> > > case
>> > > > >> > > > of
>> > > > >> > > > > unclean leader election, which is listed in the future
>> work.
>> > > Is
>> > > > >> this
>> > > > >> > > > > understanding correct?
>> > > > >> > > > >
>> > > > >> > > > > I have updated the KIP to specify that the leader_epoch
>> > > returned
>> > > > >> by
>> > > > >> > > > > position() should be the largest leader_epoch of those
>> > already
>> > > > >> > consumed
>> > > > >> > > > > messages whose offset < position. If no message has been
>> > > > consumed
>> > > > >> > since
>> > > > >> > > > > consumer initialization, the leader_epoch from seek() or
>> > > > >> > > > > OffsetFetchResponse should be used. The offset included
>> in
>> > the
>> > > > >> > > > > OffsetCommitRequest will also be determined in the
>> similar
>> > > > manner.
>> > > > >> > > > >
>> > > > >> > > > >
>> > > > >> > > > >>
>> > > > >> > > > >> 62. I am wondering if we should return the partition
>> epoch
>> > in
>> > > > the
>> > > > >> > > fetch
>> > > > >> > > > >> response as well. In the current proposal, if a topic is
>> > > > >> recreated
>> > > > >> > and
>> > > > >> > > > the
>> > > > >> > > > >> new leader is on the same broker as the old one, there
>> is
>> > > > >> nothing to
>> > > > >> > > > force
>> > > > >> > > > >> the metadata refresh in the client. So, the client may
>> > still
>> > > > >> > associate
>> > > > >> > > > the
>> > > > >> > > > >> offset with the old partition epoch.
>> > > > >> > > > >>
>> > > > >> > > > >
>> > > > >> > > > > Could you help me understand the problem if a client
>> > > associates
>> > > > >> old
>> > > > >> > > > > partition_epoch (or the topic_epoch as of the current
>> KIP)
>> > > with
>> > > > >> the
>> > > > >> > > > offset?
>> > > > >> > > > > The main purpose of the topic_epoch is to be able to drop
>> > > > >> > leader_epoch
>> > > > >> > > > to 0
>> > > > >> > > > > after a partition is deleted and re-created. I guess you
>> may
>> > > be
>> > > > >> > > thinking
>> > > > >> > > > > about using the partition_epoch to detect that the
>> committed
>> > > > >> offset
>> > > > >> > is
>> > > > >> > > > > invalid? In that case, I am wondering if the alternative
>> > > > approach
>> > > > >> > > > described
>> > > > >> > > > > in 60) would be reasonable.
>> > > > >> > > > >
>> > > > >> > > > >
>> > > > >> > > > >>
>> > > > >> > > > >> 63. There is some subtle coordination between the
>> > > > >> > LeaderAndIsrRequest
>> > > > >> > > > and
>> > > > >> > > > >> UpdateMetadataRequest. Currently, when a leader changes,
>> > the
>> > > > >> > > controller
>> > > > >> > > > >> first sends the LeaderAndIsrRequest to the assigned
>> > replicas
>> > > > and
>> > > > >> the
>> > > > >> > > > >> UpdateMetadataRequest to every broker. So, there could
>> be a
>> > > > small
>> > > > >> > > window
>> > > > >> > > > >> when the leader already receives the new partition
>> epoch in
>> > > the
>> > > > >> > > > >> LeaderAndIsrRequest, but the metadata cache in the
>> broker
>> > > > hasn't
>> > > > >> > been
>> > > > >> > > > >> updated with the latest partition epoch. Not sure what's
>> > the
>> > > > best
>> > > > >> > way
>> > > > >> > > to
>> > > > >> > > > >> address this issue. Perhaps we can update the metadata
>> > cache
>> > > on
>> > > > >> the
>> > > > >> > > > broker
>> > > > >> > > > >> with both LeaderAndIsrRequest and UpdateMetadataRequest.
>> > The
>> > > > >> > challenge
>> > > > >> > > > is
>> > > > >> > > > >> that the two have slightly different data. For example,
>> > only
>> > > > the
>> > > > >> > > latter
>> > > > >> > > > >> has
>> > > > >> > > > >> all endpoints.
>> > > > >> > > > >>
>> > > > >> > > > >
>> > > > >> > > > > I am not sure whether this is a problem. Could you
>> explain a
>> > > bit
>> > > > >> more
>> > > > >> > > > what
>> > > > >> > > > > specific problem this small window can cause?
>> > > > >> > > > >
>> > > > >> > > > > Since client can fetch metadata from any broker in the
>> > > cluster,
>> > > > >> and
>> > > > >> > > given
>> > > > >> > > > > that different brokers receive request (e.g.
>> > > LeaderAndIsrRequest
>> > > > >> and
>> > > > >> > > > > UpdateMetadataRequest) in arbitrary order, the metadata
>> > > received
>> > > > >> by
>> > > > >> > > > client
>> > > > >> > > > > can be in arbitrary order (either newer or older)
>> compared
>> > to
>> > > > the
>> > > > >> > > > broker's
>> > > > >> > > > > leadership state even if a given broker receives
>> > > > >> LeaderAndIsrRequest
>> > > > >> > > and
>> > > > >> > > > > UpdateMetadataRequest simultaneously. So I am not sure
>> it is
>> > > > >> useful
>> > > > >> > to
>> > > > >> > > > > update broker's cache with LeaderAndIsrRequest.
>> > > > >> > > > >
>> > > > >> > > > >
>> > > > >> > > > >> 64. The enforcement of leader epoch in Offset commit: We
>> > > allow
>> > > > a
>> > > > >> > > > consumer
>> > > > >> > > > >> to set an arbitrary offset. So it's possible for
>> offsets or
>> > > > >> leader
>> > > > >> > > epoch
>> > > > >> > > > >> to
>> > > > >> > > > >> go backwards. I am not sure if we could always enforce
>> that
>> > > the
>> > > > >> > leader
>> > > > >> > > > >> epoch only goes up on the broker.
>> > > > >> > > > >>
>> > > > >> > > > >
>> > > > >> > > > > Sure. I have removed this check from the KIP.
>> > > > >> > > > >
>> > > > >> > > > > BTW, we can probably still ensure that the leader_epoch
>> > always
>> > > > >> > increase
>> > > > >> > > > if
>> > > > >> > > > > the leader_epoch used with offset commit is the
>> > > max(leader_epoch
>> > > > >> of
>> > > > >> > the
>> > > > >> > > > > message with offset = the committed offset - 1, the
>> largest
>> > > > known
>> > > > >> > > > > leader_epoch from the metadata). But I don't have a good
>> > > > use-case
>> > > > >> for
>> > > > >> > > > this
>> > > > >> > > > > alternative definition. So I choose the keep the KIP
>> simple
>> > by
>> > > > >> > > requiring
>> > > > >> > > > > leader_epoch to always increase.
>> > > > >> > > > >
>> > > > >> > > > >
>> > > > >> > > > >> 65. Good point on handling missing partition epoch due
>> to
>> > > topic
>> > > > >> > > > deletion.
>> > > > >> > > > >> Another potential way to address this is to additionally
>> > > > >> propagate
>> > > > >> > the
>> > > > >> > > > >> global partition epoch to brokers and the clients. This
>> > way,
>> > > > >> when a
>> > > > >> > > > >> partition epoch is missing, we can use the global
>> partition
>> > > > >> epoch to
>> > > > >> > > > >> reason
>> > > > >> > > > >> about which metadata is more recent.
>> > > > >> > > > >>
>> > > > >> > > > >
>> > > > >> > > > > This is a great idea. The global epoch can be used to
>> order
>> > > the
>> > > > >> > > metadata
>> > > > >> > > > > and help us recognize the more recent metadata if a topic
>> > (or
>> > > > >> > > partition)
>> > > > >> > > > is
>> > > > >> > > > > deleted and re-created.
>> > > > >> > > > >
>> > > > >> > > > > Actually, it seems we only need to propagate the global
>> > epoch
>> > > to
>> > > > >> > > brokers
>> > > > >> > > > > and clients without propagating this epoch on a
>> per-topic or
>> > > > >> > > > per-partition
>> > > > >> > > > > basic. Doing so would simply interface changes made this
>> > KIP.
>> > > > Does
>> > > > >> > this
>> > > > >> > > > > approach sound reasonable?
>> > > > >> > > > >
>> > > > >> > > > >
>> > > > >> > > > >> 66. A client may also get an offset by time using the
>> > > > >> > offsetForTimes()
>> > > > >> > > > >> api.
>> > > > >> > > > >> So, we probably want to include offsetInternalMetadata
>> in
>> > > > >> > > > >> OffsetAndTimestamp
>> > > > >> > > > >> as well.
>> > > > >> > > > >>
>> > > > >> > > > >
>> > > > >> > > > > You are right. This probably also requires us to change
>> the
>> > > > >> > > > > ListOffsetRequest as well. I will update the KIP after we
>> > > agree
>> > > > on
>> > > > >> > the
>> > > > >> > > > > solution for 65).
>> > > > >> > > > >
>> > > > >> > > > >
>> > > > >> > > > >>
>> > > > >> > > > >> 67. InteralMetadata can be a bit confusing with the
>> > metadata
>> > > > >> field
>> > > > >> > > > already
>> > > > >> > > > >> there. Perhaps we can just call it OffsetEpoch. It
>> might be
>> > > > >> useful
>> > > > >> > to
>> > > > >> > > > make
>> > > > >> > > > >> OffsetEpoch printable at least for debugging purpose.
>> Once
>> > > you
>> > > > do
>> > > > >> > > that,
>> > > > >> > > > we
>> > > > >> > > > >> are already exposing the internal fields. So, not sure
>> if
>> > > it's
>> > > > >> worth
>> > > > >> > > > >> hiding
>> > > > >> > > > >> them. If we do want to hide them, perhaps we can have
>> sth
>> > > like
>> > > > >> the
>> > > > >> > > > >> following. The binary encoding is probably more
>> efficient
>> > > than
>> > > > >> JSON
>> > > > >> > > for
>> > > > >> > > > >> external storage.
>> > > > >> > > > >>
>> > > > >> > > > >> OffsetEpoch {
>> > > > >> > > > >> static OffsetEpoch decode(byte[]);
>> > > > >> > > > >>
>> > > > >> > > > >> public byte[] encode();
>> > > > >> > > > >>
>> > > > >> > > > >> public String toString();
>> > > > >> > > > >> }
>> > > > >> > > > >>
>> > > > >> > > > >
>> > > > >> > > > > Thanks much. I like this solution. I have updated the KIP
>> > > > >> > accordingly.
>> > > > >> > > > >
>> > > > >> > > > >
>> > > > >> > > > >
>> > > > >> > > > >>
>> > > > >> > > > >> Jun
>> > > > >> > > > >>
>> > > > >> > > > >> On Mon, Jan 8, 2018 at 4:22 PM, Dong Lin <
>> > > lindon...@gmail.com>
>> > > > >> > wrote:
>> > > > >> > > > >>
>> > > > >> > > > >> > Hey Jason,
>> > > > >> > > > >> >
>> > > > >> > > > >> > Certainly. This sounds good. I have updated the KIP to
>> > > > clarity
>> > > > >> > that
>> > > > >> > > > the
>> > > > >> > > > >> > global epoch will be incremented by 1 each time a
>> topic
>> > is
>> > > > >> > deleted.
>> > > > >> > > > >> >
>> > > > >> > > > >> > Thanks,
>> > > > >> > > > >> > Dong
>> > > > >> > > > >> >
>> > > > >> > > > >> > On Mon, Jan 8, 2018 at 4:09 PM, Jason Gustafson <
>> > > > >> > ja...@confluent.io
>> > > > >> > > >
>> > > > >> > > > >> > wrote:
>> > > > >> > > > >> >
>> > > > >> > > > >> > > Hi Dong,
>> > > > >> > > > >> > >
>> > > > >> > > > >> > >
>> > > > >> > > > >> > > I think your approach will allow user to distinguish
>> > > > between
>> > > > >> the
>> > > > >> > > > >> metadata
>> > > > >> > > > >> > > > before and after the topic deletion. I also agree
>> > that
>> > > > this
>> > > > >> > can
>> > > > >> > > be
>> > > > >> > > > >> > > > potentially be useful to user. I am just not very
>> > sure
>> > > > >> whether
>> > > > >> > > we
>> > > > >> > > > >> > already
>> > > > >> > > > >> > > > have a good use-case to make the additional
>> > complexity
>> > > > >> > > worthwhile.
>> > > > >> > > > >> It
>> > > > >> > > > >> > > seems
>> > > > >> > > > >> > > > that this feature is kind of independent of the
>> main
>> > > > >> problem
>> > > > >> > of
>> > > > >> > > > this
>> > > > >> > > > >> > KIP.
>> > > > >> > > > >> > > > Could we add this as a future work?
>> > > > >> > > > >> > >
>> > > > >> > > > >> > >
>> > > > >> > > > >> > > Do you think it's fair if we bump the topic epoch on
>> > > > deletion
>> > > > >> > and
>> > > > >> > > > >> leave
>> > > > >> > > > >> > > propagation of the epoch for deleted topics for
>> future
>> > > > work?
>> > > > >> I
>> > > > >> > > don't
>> > > > >> > > > >> > think
>> > > > >> > > > >> > > this adds much complexity and it makes the behavior
>> > > > >> consistent:
>> > > > >> > > > every
>> > > > >> > > > >> > topic
>> > > > >> > > > >> > > mutation results in an epoch bump.
>> > > > >> > > > >> > >
>> > > > >> > > > >> > > Thanks,
>> > > > >> > > > >> > > Jason
>> > > > >> > > > >> > >
>> > > > >> > > > >> > > On Mon, Jan 8, 2018 at 3:14 PM, Dong Lin <
>> > > > >> lindon...@gmail.com>
>> > > > >> > > > wrote:
>> > > > >> > > > >> > >
>> > > > >> > > > >> > > > Hey Ismael,
>> > > > >> > > > >> > > >
>> > > > >> > > > >> > > > I guess we actually need user to see this field so
>> > that
>> > > > >> user
>> > > > >> > can
>> > > > >> > > > >> store
>> > > > >> > > > >> > > this
>> > > > >> > > > >> > > > value in the external store together with the
>> offset.
>> > > We
>> > > > >> just
>> > > > >> > > > prefer
>> > > > >> > > > >> > the
>> > > > >> > > > >> > > > value to be opaque to discourage most users from
>> > > > >> interpreting
>> > > > >> > > this
>> > > > >> > > > >> > value.
>> > > > >> > > > >> > > > One more advantage of using such an opaque field
>> is
>> > to
>> > > be
>> > > > >> able
>> > > > >> > > to
>> > > > >> > > > >> > evolve
>> > > > >> > > > >> > > > the information (or schema) of this value without
>> > > > changing
>> > > > >> > > > consumer
>> > > > >> > > > >> API
>> > > > >> > > > >> > > in
>> > > > >> > > > >> > > > the future.
>> > > > >> > > > >> > > >
>> > > > >> > > > >> > > > I also thinking it is probably OK for user to be
>> able
>> > > to
>> > > > >> > > interpret
>> > > > >> > > > >> this
>> > > > >> > > > >> > > > value, particularly for those advanced users.
>> > > > >> > > > >> > > >
>> > > > >> > > > >> > > > Thanks,
>> > > > >> > > > >> > > > Dong
>> > > > >> > > > >> > > >
>> > > > >> > > > >> > > > On Mon, Jan 8, 2018 at 2:34 PM, Ismael Juma <
>> > > > >> > ism...@juma.me.uk>
>> > > > >> > > > >> wrote:
>> > > > >> > > > >> > > >
>> > > > >> > > > >> > > > > On Fri, Jan 5, 2018 at 7:15 PM, Jason Gustafson
>> <
>> > > > >> > > > >> ja...@confluent.io>
>> > > > >> > > > >> > > > > wrote:
>> > > > >> > > > >> > > > > >
>> > > > >> > > > >> > > > > > class OffsetAndMetadata {
>> > > > >> > > > >> > > > > > long offset;
>> > > > >> > > > >> > > > > > byte[] offsetMetadata;
>> > > > >> > > > >> > > > > > String metadata;
>> > > > >> > > > >> > > > > > }
>> > > > >> > > > >> > > > >
>> > > > >> > > > >> > > > >
>> > > > >> > > > >> > > > > > Admittedly, the naming is a bit annoying, but
>> we
>> > > can
>> > > > >> > > probably
>> > > > >> > > > >> come
>> > > > >> > > > >> > up
>> > > > >> > > > >> > > > > with
>> > > > >> > > > >> > > > > > something better. Internally the byte array
>> would
>> > > > have
>> > > > >> a
>> > > > >> > > > >> version.
>> > > > >> > > > >> > If
>> > > > >> > > > >> > > in
>> > > > >> > > > >> > > > > the
>> > > > >> > > > >> > > > > > future we have anything else we need to add,
>> we
>> > can
>> > > > >> update
>> > > > >> > > the
>> > > > >> > > > >> > > version
>> > > > >> > > > >> > > > > and
>> > > > >> > > > >> > > > > > we wouldn't need any new APIs.
>> > > > >> > > > >> > > > > >
>> > > > >> > > > >> > > > >
>> > > > >> > > > >> > > > > We can also add fields to a class in a
>> compatible
>> > > way.
>> > > > >> So,
>> > > > >> > it
>> > > > >> > > > >> seems
>> > > > >> > > > >> > to
>> > > > >> > > > >> > > me
>> > > > >> > > > >> > > > > that the main advantage of the byte array is
>> that
>> > > it's
>> > > > >> > opaque
>> > > > >> > > to
>> > > > >> > > > >> the
>> > > > >> > > > >> > > > user.
>> > > > >> > > > >> > > > > Is that correct? If so, we could also add any
>> > opaque
>> > > > >> > metadata
>> > > > >> > > > in a
>> > > > >> > > > >> > > > subclass
>> > > > >> > > > >> > > > > so that users don't even see it (unless they
>> cast
>> > it,
>> > > > but
>> > > > >> > then
>> > > > >> > > > >> > they're
>> > > > >> > > > >> > > on
>> > > > >> > > > >> > > > > their own).
>> > > > >> > > > >> > > > >
>> > > > >> > > > >> > > > > Ismael
>> > > > >> > > > >> > > > >
>> > > > >> > > > >> > > > > The corresponding seek() and position() APIs
>> might
>> > > look
>> > > > >> > > > something
>> > > > >> > > > >> > like
>> > > > >> > > > >> > > > > this:
>> > > > >> > > > >> > > > > >
>> > > > >> > > > >> > > > > > void seek(TopicPartition partition, long
>> offset,
>> > > > byte[]
>> > > > >> > > > >> > > > offsetMetadata);
>> > > > >> > > > >> > > > > > byte[] positionMetadata(TopicPartition
>> > partition);
>> > > > >> > > > >> > > > > >
>> > > > >> > > > >> > > > > > What do you think?
>> > > > >> > > > >> > > > > >
>> > > > >> > > > >> > > > > > Thanks,
>> > > > >> > > > >> > > > > > Jason
>> > > > >> > > > >> > > > > >
>> > > > >> > > > >> > > > > > On Thu, Jan 4, 2018 at 7:04 PM, Dong Lin <
>> > > > >> > > lindon...@gmail.com
>> > > > >> > > > >
>> > > > >> > > > >> > > wrote:
>> > > > >> > > > >> > > > > >
>> > > > >> > > > >> > > > > > > Hey Jun, Jason,
>> > > > >> > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > Thanks much for all the feedback. I have
>> > updated
>> > > > the
>> > > > >> KIP
>> > > > >> > > > >> based on
>> > > > >> > > > >> > > the
>> > > > >> > > > >> > > > > > > latest discussion. Can you help check
>> whether
>> > it
>> > > > >> looks
>> > > > >> > > good?
>> > > > >> > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > Thanks,
>> > > > >> > > > >> > > > > > > Dong
>> > > > >> > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > On Thu, Jan 4, 2018 at 5:36 PM, Dong Lin <
>> > > > >> > > > lindon...@gmail.com
>> > > > >> > > > >> >
>> > > > >> > > > >> > > > wrote:
>> > > > >> > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > > Hey Jun,
>> > > > >> > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > > > Hmm... thinking about this more, I am not
>> > sure
>> > > > that
>> > > > >> > the
>> > > > >> > > > >> > proposed
>> > > > >> > > > >> > > > API
>> > > > >> > > > >> > > > > is
>> > > > >> > > > >> > > > > > > > sufficient. For users that store offset
>> > > > >> externally, we
>> > > > >> > > > >> probably
>> > > > >> > > > >> > > > need
>> > > > >> > > > >> > > > > > > extra
>> > > > >> > > > >> > > > > > > > API to return the leader_epoch and
>> > > > partition_epoch
>> > > > >> for
>> > > > >> > > all
>> > > > >> > > > >> > > > partitions
>> > > > >> > > > >> > > > > > > that
>> > > > >> > > > >> > > > > > > > consumers are consuming. I suppose these
>> > users
>> > > > >> > currently
>> > > > >> > > > use
>> > > > >> > > > >> > > > > position()
>> > > > >> > > > >> > > > > > > to
>> > > > >> > > > >> > > > > > > > get the offset. Thus we probably need a
>> new
>> > > > method
>> > > > >> > > > >> > > > > > positionWithEpoch(..)
>> > > > >> > > > >> > > > > > > to
>> > > > >> > > > >> > > > > > > > return <offset, partition_epoch,
>> > leader_epoch>.
>> > > > >> Does
>> > > > >> > > this
>> > > > >> > > > >> sound
>> > > > >> > > > >> > > > > > > reasonable?
>> > > > >> > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > > > Thanks,
>> > > > >> > > > >> > > > > > > > Dong
>> > > > >> > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > > > On Thu, Jan 4, 2018 at 5:26 PM, Jun Rao <
>> > > > >> > > j...@confluent.io
>> > > > >> > > > >
>> > > > >> > > > >> > > wrote:
>> > > > >> > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > > >> Hi, Dong,
>> > > > >> > > > >> > > > > > > >>
>> > > > >> > > > >> > > > > > > >> Yes, that's what I am thinking.
>> OffsetEpoch
>> > > will
>> > > > >> be
>> > > > >> > > > >> composed
>> > > > >> > > > >> > of
>> > > > >> > > > >> > > > > > > >> (partition_epoch,
>> > > > >> > > > >> > > > > > > >> leader_epoch).
>> > > > >> > > > >> > > > > > > >>
>> > > > >> > > > >> > > > > > > >> Thanks,
>> > > > >> > > > >> > > > > > > >>
>> > > > >> > > > >> > > > > > > >> Jun
>> > > > >> > > > >> > > > > > > >>
>> > > > >> > > > >> > > > > > > >>
>> > > > >> > > > >> > > > > > > >> On Thu, Jan 4, 2018 at 4:22 PM, Dong Lin
>> <
>> > > > >> > > > >> lindon...@gmail.com
>> > > > >> > > > >> > >
>> > > > >> > > > >> > > > > wrote:
>> > > > >> > > > >> > > > > > > >>
>> > > > >> > > > >> > > > > > > >> > Hey Jun,
>> > > > >> > > > >> > > > > > > >> >
>> > > > >> > > > >> > > > > > > >> > Thanks much. I like the the new API
>> that
>> > you
>> > > > >> > > proposed.
>> > > > >> > > > I
>> > > > >> > > > >> am
>> > > > >> > > > >> > > not
>> > > > >> > > > >> > > > > sure
>> > > > >> > > > >> > > > > > > >> what
>> > > > >> > > > >> > > > > > > >> > you exactly mean by offset_epoch. I
>> > suppose
>> > > > >> that we
>> > > > >> > > can
>> > > > >> > > > >> use
>> > > > >> > > > >> > > the
>> > > > >> > > > >> > > > > pair
>> > > > >> > > > >> > > > > > > of
>> > > > >> > > > >> > > > > > > >> > (partition_epoch, leader_epoch) as the
>> > > > >> > offset_epoch,
>> > > > >> > > > >> right?
>> > > > >> > > > >> > > > > > > >> >
>> > > > >> > > > >> > > > > > > >> > Thanks,
>> > > > >> > > > >> > > > > > > >> > Dong
>> > > > >> > > > >> > > > > > > >> >
>> > > > >> > > > >> > > > > > > >> > On Thu, Jan 4, 2018 at 4:02 PM, Jun
>> Rao <
>> > > > >> > > > >> j...@confluent.io>
>> > > > >> > > > >> > > > wrote:
>> > > > >> > > > >> > > > > > > >> >
>> > > > >> > > > >> > > > > > > >> > > Hi, Dong,
>> > > > >> > > > >> > > > > > > >> > >
>> > > > >> > > > >> > > > > > > >> > > Got it. The api that you proposed
>> works.
>> > > The
>> > > > >> > > question
>> > > > >> > > > >> is
>> > > > >> > > > >> > > > whether
>> > > > >> > > > >> > > > > > > >> that's
>> > > > >> > > > >> > > > > > > >> > the
>> > > > >> > > > >> > > > > > > >> > > api that we want to have in the long
>> > term.
>> > > > My
>> > > > >> > > concern
>> > > > >> > > > >> is
>> > > > >> > > > >> > > that
>> > > > >> > > > >> > > > > > while
>> > > > >> > > > >> > > > > > > >> the
>> > > > >> > > > >> > > > > > > >> > api
>> > > > >> > > > >> > > > > > > >> > > change is simple, the new api seems
>> > harder
>> > > > to
>> > > > >> > > explain
>> > > > >> > > > >> and
>> > > > >> > > > >> > > use.
>> > > > >> > > > >> > > > > For
>> > > > >> > > > >> > > > > > > >> > example,
>> > > > >> > > > >> > > > > > > >> > > a consumer storing offsets externally
>> > now
>> > > > >> needs
>> > > > >> > to
>> > > > >> > > > call
>> > > > >> > > > >> > > > > > > >> > > waitForMetadataUpdate() after calling
>> > > > seek().
>> > > > >> > > > >> > > > > > > >> > >
>> > > > >> > > > >> > > > > > > >> > > An alternative approach is to make
>> the
>> > > > >> following
>> > > > >> > > > >> > compatible
>> > > > >> > > > >> > > > api
>> > > > >> > > > >> > > > > > > >> changes
>> > > > >> > > > >> > > > > > > >> > in
>> > > > >> > > > >> > > > > > > >> > > Consumer.
>> > > > >> > > > >> > > > > > > >> > > * Add an additional OffsetEpoch
>> field in
>> > > > >> > > > >> > OffsetAndMetadata.
>> > > > >> > > > >> > > > (no
>> > > > >> > > > >> > > > > > need
>> > > > >> > > > >> > > > > > > >> to
>> > > > >> > > > >> > > > > > > >> > > change the CommitSync() api)
>> > > > >> > > > >> > > > > > > >> > > * Add a new api seek(TopicPartition
>> > > > partition,
>> > > > >> > long
>> > > > >> > > > >> > offset,
>> > > > >> > > > >> > > > > > > >> OffsetEpoch
>> > > > >> > > > >> > > > > > > >> > > offsetEpoch). We can potentially
>> > deprecate
>> > > > the
>> > > > >> > old
>> > > > >> > > > api
>> > > > >> > > > >> > > > > > > >> > seek(TopicPartition
>> > > > >> > > > >> > > > > > > >> > > partition, long offset) in the
>> future.
>> > > > >> > > > >> > > > > > > >> > >
>> > > > >> > > > >> > > > > > > >> > > The alternative approach has similar
>> > > amount
>> > > > of
>> > > > >> > api
>> > > > >> > > > >> changes
>> > > > >> > > > >> > > as
>> > > > >> > > > >> > > > > > yours
>> > > > >> > > > >> > > > > > > >> but
>> > > > >> > > > >> > > > > > > >> > has
>> > > > >> > > > >> > > > > > > >> > > the following benefits.
>> > > > >> > > > >> > > > > > > >> > > 1. The api works in a similar way as
>> how
>> > > > >> offset
>> > > > >> > > > >> management
>> > > > >> > > > >> > > > works
>> > > > >> > > > >> > > > > > now
>> > > > >> > > > >> > > > > > > >> and
>> > > > >> > > > >> > > > > > > >> > is
>> > > > >> > > > >> > > > > > > >> > > probably what we want in the long
>> term.
>> > > > >> > > > >> > > > > > > >> > > 2. It can reset offsets better when
>> > there
>> > > is
>> > > > >> data
>> > > > >> > > > loss
>> > > > >> > > > >> due
>> > > > >> > > > >> > > to
>> > > > >> > > > >> > > > > > > unclean
>> > > > >> > > > >> > > > > > > >> > > leader election or correlated replica
>> > > > failure.
>> > > > >> > > > >> > > > > > > >> > > 3. It can reset offsets better when
>> > topic
>> > > is
>> > > > >> > > > recreated.
>> > > > >> > > > >> > > > > > > >> > >
>> > > > >> > > > >> > > > > > > >> > > Thanks,
>> > > > >> > > > >> > > > > > > >> > >
>> > > > >> > > > >> > > > > > > >> > > Jun
>> > > > >> > > > >> > > > > > > >> > >
>> > > > >> > > > >> > > > > > > >> > >
>> > > > >> > > > >> > > > > > > >> > > On Thu, Jan 4, 2018 at 2:05 PM, Dong
>> > Lin <
>> > > > >> > > > >> > > lindon...@gmail.com
>> > > > >> > > > >> > > > >
>> > > > >> > > > >> > > > > > > wrote:
>> > > > >> > > > >> > > > > > > >> > >
>> > > > >> > > > >> > > > > > > >> > > > Hey Jun,
>> > > > >> > > > >> > > > > > > >> > > >
>> > > > >> > > > >> > > > > > > >> > > > Yeah I agree that ideally we don't
>> > want
>> > > an
>> > > > >> ever
>> > > > >> > > > >> growing
>> > > > >> > > > >> > > > global
>> > > > >> > > > >> > > > > > > >> metadata
>> > > > >> > > > >> > > > > > > >> > > > version. I just think it may be
>> more
>> > > > >> desirable
>> > > > >> > to
>> > > > >> > > > >> keep
>> > > > >> > > > >> > the
>> > > > >> > > > >> > > > > > > consumer
>> > > > >> > > > >> > > > > > > >> API
>> > > > >> > > > >> > > > > > > >> > > > simple.
>> > > > >> > > > >> > > > > > > >> > > >
>> > > > >> > > > >> > > > > > > >> > > > In my current proposal, metadata
>> > version
>> > > > >> > returned
>> > > > >> > > > in
>> > > > >> > > > >> the
>> > > > >> > > > >> > > > fetch
>> > > > >> > > > >> > > > > > > >> response
>> > > > >> > > > >> > > > > > > >> > > > will be stored with the offset
>> > together.
>> > > > >> More
>> > > > >> > > > >> > > specifically,
>> > > > >> > > > >> > > > > the
>> > > > >> > > > >> > > > > > > >> > > > metadata_epoch in the new offset
>> topic
>> > > > >> schema
>> > > > >> > > will
>> > > > >> > > > be
>> > > > >> > > > >> > the
>> > > > >> > > > >> > > > > > largest
>> > > > >> > > > >> > > > > > > >> > > > metadata_epoch from all the
>> > > > MetadataResponse
>> > > > >> > and
>> > > > >> > > > >> > > > FetchResponse
>> > > > >> > > > >> > > > > > > ever
>> > > > >> > > > >> > > > > > > >> > > > received by this consumer.
>> > > > >> > > > >> > > > > > > >> > > >
>> > > > >> > > > >> > > > > > > >> > > > We probably don't have to change
>> the
>> > > > >> consumer
>> > > > >> > API
>> > > > >> > > > for
>> > > > >> > > > >> > > > > > > >> > > > commitSync(Map<TopicPartition,
>> > > > >> > > OffsetAndMetadata>).
>> > > > >> > > > >> If
>> > > > >> > > > >> > > user
>> > > > >> > > > >> > > > > > calls
>> > > > >> > > > >> > > > > > > >> > > > commitSync(...) to commit offset 10
>> > for
>> > > a
>> > > > >> given
>> > > > >> > > > >> > partition,
>> > > > >> > > > >> > > > for
>> > > > >> > > > >> > > > > > > most
>> > > > >> > > > >> > > > > > > >> > > > use-cases, this consumer instance
>> > should
>> > > > >> have
>> > > > >> > > > >> consumed
>> > > > >> > > > >> > > > message
>> > > > >> > > > >> > > > > > > with
>> > > > >> > > > >> > > > > > > >> > > offset
>> > > > >> > > > >> > > > > > > >> > > > 9 from this partition, in which
>> case
>> > the
>> > > > >> > consumer
>> > > > >> > > > can
>> > > > >> > > > >> > > > remember
>> > > > >> > > > >> > > > > > and
>> > > > >> > > > >> > > > > > > >> use
>> > > > >> > > > >> > > > > > > >> > > the
>> > > > >> > > > >> > > > > > > >> > > > metadata_epoch from the
>> corresponding
>> > > > >> > > FetchResponse
>> > > > >> > > > >> when
>> > > > >> > > > >> > > > > > > committing
>> > > > >> > > > >> > > > > > > >> > > offset.
>> > > > >> > > > >> > > > > > > >> > > > If user calls commitSync(..) to
>> commit
>> > > > >> offset
>> > > > >> > 10
>> > > > >> > > > for
>> > > > >> > > > >> a
>> > > > >> > > > >> > > given
>> > > > >> > > > >> > > > > > > >> partition
>> > > > >> > > > >> > > > > > > >> > > > without having consumed the message
>> > with
>> > > > >> > offset 9
>> > > > >> > > > >> using
>> > > > >> > > > >> > > this
>> > > > >> > > > >> > > > > > > >> consumer
>> > > > >> > > > >> > > > > > > >> > > > instance, this is probably an
>> advanced
>> > > > >> > use-case.
>> > > > >> > > In
>> > > > >> > > > >> this
>> > > > >> > > > >> > > > case
>> > > > >> > > > >> > > > > > the
>> > > > >> > > > >> > > > > > > >> > > advanced
>> > > > >> > > > >> > > > > > > >> > > > user can retrieve the
>> metadata_epoch
>> > > using
>> > > > >> the
>> > > > >> > > > newly
>> > > > >> > > > >> > added
>> > > > >> > > > >> > > > > > > >> > > metadataEpoch()
>> > > > >> > > > >> > > > > > > >> > > > API after it fetches the message
>> with
>> > > > >> offset 9
>> > > > >> > > > >> (probably
>> > > > >> > > > >> > > > from
>> > > > >> > > > >> > > > > > > >> another
>> > > > >> > > > >> > > > > > > >> > > > consumer instance) and encode this
>> > > > >> > metadata_epoch
>> > > > >> > > > in
>> > > > >> > > > >> the
>> > > > >> > > > >> > > > > > > >> > > > string OffsetAndMetadata.metadata.
>> Do
>> > > you
>> > > > >> think
>> > > > >> > > > this
>> > > > >> > > > >> > > > solution
>> > > > >> > > > >> > > > > > > would
>> > > > >> > > > >> > > > > > > >> > work?
>> > > > >> > > > >> > > > > > > >> > > >
>> > > > >> > > > >> > > > > > > >> > > > By "not sure that I fully
>> understand
>> > > your
>> > > > >> > latest
>> > > > >> > > > >> > > > suggestion",
>> > > > >> > > > >> > > > > > are
>> > > > >> > > > >> > > > > > > >> you
>> > > > >> > > > >> > > > > > > >> > > > referring to solution related to
>> > unclean
>> > > > >> leader
>> > > > >> > > > >> election
>> > > > >> > > > >> > > > using
>> > > > >> > > > >> > > > > > > >> > > leader_epoch
>> > > > >> > > > >> > > > > > > >> > > > in my previous email?
>> > > > >> > > > >> > > > > > > >> > > >
>> > > > >> > > > >> > > > > > > >> > > > Thanks,
>> > > > >> > > > >> > > > > > > >> > > > Dong
>> > > > >> > > > >> > > > > > > >> > > >
>> > > > >> > > > >> > > > > > > >> > > > On Thu, Jan 4, 2018 at 1:33 PM, Jun
>> > Rao
>> > > <
>> > > > >> > > > >> > j...@confluent.io
>> > > > >> > > > >> > > >
>> > > > >> > > > >> > > > > > wrote:
>> > > > >> > > > >> > > > > > > >> > > >
>> > > > >> > > > >> > > > > > > >> > > > > Hi, Dong,
>> > > > >> > > > >> > > > > > > >> > > > >
>> > > > >> > > > >> > > > > > > >> > > > > Not sure that I fully understand
>> > your
>> > > > >> latest
>> > > > >> > > > >> > suggestion.
>> > > > >> > > > >> > > > > > > >> Returning an
>> > > > >> > > > >> > > > > > > >> > > > ever
>> > > > >> > > > >> > > > > > > >> > > > > growing global metadata version
>> > itself
>> > > > is
>> > > > >> no
>> > > > >> > > > ideal,
>> > > > >> > > > >> > but
>> > > > >> > > > >> > > is
>> > > > >> > > > >> > > > > > fine.
>> > > > >> > > > >> > > > > > > >> My
>> > > > >> > > > >> > > > > > > >> > > > > question is whether the metadata
>> > > version
>> > > > >> > > returned
>> > > > >> > > > >> in
>> > > > >> > > > >> > the
>> > > > >> > > > >> > > > > fetch
>> > > > >> > > > >> > > > > > > >> > response
>> > > > >> > > > >> > > > > > > >> > > > > needs to be stored with the
>> offset
>> > > > >> together
>> > > > >> > if
>> > > > >> > > > >> offsets
>> > > > >> > > > >> > > are
>> > > > >> > > > >> > > > > > > stored
>> > > > >> > > > >> > > > > > > >> > > > > externally. If so, we also have
>> to
>> > > > change
>> > > > >> the
>> > > > >> > > > >> consumer
>> > > > >> > > > >> > > API
>> > > > >> > > > >> > > > > for
>> > > > >> > > > >> > > > > > > >> > > > commitSync()
>> > > > >> > > > >> > > > > > > >> > > > > and need to worry about
>> > compatibility.
>> > > > If
>> > > > >> we
>> > > > >> > > > don't
>> > > > >> > > > >> > store
>> > > > >> > > > >> > > > the
>> > > > >> > > > >> > > > > > > >> metadata
>> > > > >> > > > >> > > > > > > >> > > > > version together with the offset,
>> > on a
>> > > > >> > consumer
>> > > > >> > > > >> > restart,
>> > > > >> > > > >> > > > > it's
>> > > > >> > > > >> > > > > > > not
>> > > > >> > > > >> > > > > > > >> > clear
>> > > > >> > > > >> > > > > > > >> > > > how
>> > > > >> > > > >> > > > > > > >> > > > > we can ensure the metadata in the
>> > > > >> consumer is
>> > > > >> > > > high
>> > > > >> > > > >> > > enough
>> > > > >> > > > >> > > > > > since
>> > > > >> > > > >> > > > > > > >> there
>> > > > >> > > > >> > > > > > > >> > > is
>> > > > >> > > > >> > > > > > > >> > > > no
>> > > > >> > > > >> > > > > > > >> > > > > metadata version to compare with.
>> > > > >> > > > >> > > > > > > >> > > > >
>> > > > >> > > > >> > > > > > > >> > > > > Thanks,
>> > > > >> > > > >> > > > > > > >> > > > >
>> > > > >> > > > >> > > > > > > >> > > > > Jun
>> > > > >> > > > >> > > > > > > >> > > > >
>> > > > >> > > > >> > > > > > > >> > > > >
>> > > > >> > > > >> > > > > > > >> > > > > On Wed, Jan 3, 2018 at 6:43 PM,
>> Dong
>> > > > Lin <
>> > > > >> > > > >> > > > > lindon...@gmail.com
>> > > > >> > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > >> > wrote:
>> > > > >> > > > >> > > > > > > >> > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > Hey Jun,
>> > > > >> > > > >> > > > > > > >> > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > Thanks much for the
>> explanation.
>> > > > >> > > > >> > > > > > > >> > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > I understand the advantage of
>> > > > >> > partition_epoch
>> > > > >> > > > >> over
>> > > > >> > > > >> > > > > > > >> metadata_epoch.
>> > > > >> > > > >> > > > > > > >> > My
>> > > > >> > > > >> > > > > > > >> > > > > > current concern is that the
>> use of
>> > > > >> > > leader_epoch
>> > > > >> > > > >> and
>> > > > >> > > > >> > > the
>> > > > >> > > > >> > > > > > > >> > > partition_epoch
>> > > > >> > > > >> > > > > > > >> > > > > > requires us considerable
>> change to
>> > > > >> > consumer's
>> > > > >> > > > >> public
>> > > > >> > > > >> > > API
>> > > > >> > > > >> > > > > to
>> > > > >> > > > >> > > > > > > take
>> > > > >> > > > >> > > > > > > >> > care
>> > > > >> > > > >> > > > > > > >> > > > of
>> > > > >> > > > >> > > > > > > >> > > > > > the case where user stores
>> offset
>> > > > >> > externally.
>> > > > >> > > > For
>> > > > >> > > > >> > > > example,
>> > > > >> > > > >> > > > > > > >> > > *consumer*.
>> > > > >> > > > >> > > > > > > >> > > > > > *commitSync*(..) would have to
>> > take
>> > > a
>> > > > >> map
>> > > > >> > > whose
>> > > > >> > > > >> > value
>> > > > >> > > > >> > > is
>> > > > >> > > > >> > > > > > > >> <offset,
>> > > > >> > > > >> > > > > > > >> > > > > metadata,
>> > > > >> > > > >> > > > > > > >> > > > > > leader epoch, partition epoch>.
>> > > > >> > > > >> > *consumer*.*seek*(...)
>> > > > >> > > > >> > > > > would
>> > > > >> > > > >> > > > > > > >> also
>> > > > >> > > > >> > > > > > > >> > > need
>> > > > >> > > > >> > > > > > > >> > > > > > leader_epoch and
>> partition_epoch
>> > as
>> > > > >> > > parameter.
>> > > > >> > > > >> > > > Technically
>> > > > >> > > > >> > > > > > we
>> > > > >> > > > >> > > > > > > >> can
>> > > > >> > > > >> > > > > > > >> > > > > probably
>> > > > >> > > > >> > > > > > > >> > > > > > still make it work in a
>> backward
>> > > > >> compatible
>> > > > >> > > > >> manner
>> > > > >> > > > >> > > after
>> > > > >> > > > >> > > > > > > careful
>> > > > >> > > > >> > > > > > > >> > > design
>> > > > >> > > > >> > > > > > > >> > > > > and
>> > > > >> > > > >> > > > > > > >> > > > > > discussion. But these changes
>> can
>> > > make
>> > > > >> the
>> > > > >> > > > >> > consumer's
>> > > > >> > > > >> > > > > > > interface
>> > > > >> > > > >> > > > > > > >> > > > > > unnecessarily complex for more
>> > users
>> > > > >> who do
>> > > > >> > > not
>> > > > >> > > > >> > store
>> > > > >> > > > >> > > > > offset
>> > > > >> > > > >> > > > > > > >> > > > externally.
>> > > > >> > > > >> > > > > > > >> > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > After thinking more about it,
>> we
>> > can
>> > > > >> > address
>> > > > >> > > > all
>> > > > >> > > > >> > > > problems
>> > > > >> > > > >> > > > > > > >> discussed
>> > > > >> > > > >> > > > > > > >> > > by
>> > > > >> > > > >> > > > > > > >> > > > > only
>> > > > >> > > > >> > > > > > > >> > > > > > using the metadata_epoch
>> without
>> > > > >> > introducing
>> > > > >> > > > >> > > > leader_epoch
>> > > > >> > > > >> > > > > or
>> > > > >> > > > >> > > > > > > the
>> > > > >> > > > >> > > > > > > >> > > > > > partition_epoch. The current
>> KIP
>> > > > >> describes
>> > > > >> > > the
>> > > > >> > > > >> > changes
>> > > > >> > > > >> > > > to
>> > > > >> > > > >> > > > > > the
>> > > > >> > > > >> > > > > > > >> > > consumer
>> > > > >> > > > >> > > > > > > >> > > > > API
>> > > > >> > > > >> > > > > > > >> > > > > > and how the new API can be
>> used if
>> > > > user
>> > > > >> > > stores
>> > > > >> > > > >> > offset
>> > > > >> > > > >> > > > > > > >> externally.
>> > > > >> > > > >> > > > > > > >> > In
>> > > > >> > > > >> > > > > > > >> > > > > order
>> > > > >> > > > >> > > > > > > >> > > > > > to address the scenario you
>> > > described
>> > > > >> > > earlier,
>> > > > >> > > > we
>> > > > >> > > > >> > can
>> > > > >> > > > >> > > > > > include
>> > > > >> > > > >> > > > > > > >> > > > > > metadata_epoch in the
>> > FetchResponse
>> > > > and
>> > > > >> the
>> > > > >> > > > >> > > > > > > LeaderAndIsrRequest.
>> > > > >> > > > >> > > > > > > >> > > > Consumer
>> > > > >> > > > >> > > > > > > >> > > > > > remembers the largest
>> > metadata_epoch
>> > > > >> from
>> > > > >> > all
>> > > > >> > > > the
>> > > > >> > > > >> > > > > > > FetchResponse
>> > > > >> > > > >> > > > > > > >> it
>> > > > >> > > > >> > > > > > > >> > > has
>> > > > >> > > > >> > > > > > > >> > > > > > received. The metadata_epoch
>> > > committed
>> > > > >> with
>> > > > >> > > the
>> > > > >> > > > >> > > offset,
>> > > > >> > > > >> > > > > > either
>> > > > >> > > > >> > > > > > > >> > within
>> > > > >> > > > >> > > > > > > >> > > > or
>> > > > >> > > > >> > > > > > > >> > > > > > outside Kafka, should be the
>> > largest
>> > > > >> > > > >> metadata_epoch
>> > > > >> > > > >> > > > across
>> > > > >> > > > >> > > > > > all
>> > > > >> > > > >> > > > > > > >> > > > > > FetchResponse and
>> MetadataResponse
>> > > > ever
>> > > > >> > > > received
>> > > > >> > > > >> by
>> > > > >> > > > >> > > this
>> > > > >> > > > >> > > > > > > >> consumer.
>> > > > >> > > > >> > > > > > > >> > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > The drawback of using only the
>> > > > >> > metadata_epoch
>> > > > >> > > > is
>> > > > >> > > > >> > that
>> > > > >> > > > >> > > we
>> > > > >> > > > >> > > > > can
>> > > > >> > > > >> > > > > > > not
>> > > > >> > > > >> > > > > > > >> > > always
>> > > > >> > > > >> > > > > > > >> > > > > do
>> > > > >> > > > >> > > > > > > >> > > > > > the smart offset reset in case
>> of
>> > > > >> unclean
>> > > > >> > > > leader
>> > > > >> > > > >> > > > election
>> > > > >> > > > >> > > > > > > which
>> > > > >> > > > >> > > > > > > >> you
>> > > > >> > > > >> > > > > > > >> > > > > > mentioned earlier. But in most
>> > case,
>> > > > >> > unclean
>> > > > >> > > > >> leader
>> > > > >> > > > >> > > > > election
>> > > > >> > > > >> > > > > > > >> > probably
>> > > > >> > > > >> > > > > > > >> > > > > > happens when consumer is not
>> > > > >> > > > >> rebalancing/restarting.
>> > > > >> > > > >> > > In
>> > > > >> > > > >> > > > > > these
>> > > > >> > > > >> > > > > > > >> > cases,
>> > > > >> > > > >> > > > > > > >> > > > > either
>> > > > >> > > > >> > > > > > > >> > > > > > consumer is not directly
>> affected
>> > by
>> > > > >> > unclean
>> > > > >> > > > >> leader
>> > > > >> > > > >> > > > > election
>> > > > >> > > > >> > > > > > > >> since
>> > > > >> > > > >> > > > > > > >> > it
>> > > > >> > > > >> > > > > > > >> > > > is
>> > > > >> > > > >> > > > > > > >> > > > > > not consuming from the end of
>> the
>> > > log,
>> > > > >> or
>> > > > >> > > > >> consumer
>> > > > >> > > > >> > can
>> > > > >> > > > >> > > > > > derive
>> > > > >> > > > >> > > > > > > >> the
>> > > > >> > > > >> > > > > > > >> > > > > > leader_epoch from the most
>> recent
>> > > > >> message
>> > > > >> > > > >> received
>> > > > >> > > > >> > > > before
>> > > > >> > > > >> > > > > it
>> > > > >> > > > >> > > > > > > >> sees
>> > > > >> > > > >> > > > > > > >> > > > > > OffsetOutOfRangeException. So
>> I am
>> > > not
>> > > > >> sure
>> > > > >> > > it
>> > > > >> > > > is
>> > > > >> > > > >> > > worth
>> > > > >> > > > >> > > > > > adding
>> > > > >> > > > >> > > > > > > >> the
>> > > > >> > > > >> > > > > > > >> > > > > > leader_epoch to consumer API to
>> > > > address
>> > > > >> the
>> > > > >> > > > >> > remaining
>> > > > >> > > > >> > > > > corner
>> > > > >> > > > >> > > > > > > >> case.
>> > > > >> > > > >> > > > > > > >> > > What
>> > > > >> > > > >> > > > > > > >> > > > > do
>> > > > >> > > > >> > > > > > > >> > > > > > you think?
>> > > > >> > > > >> > > > > > > >> > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > Thanks,
>> > > > >> > > > >> > > > > > > >> > > > > > Dong
>> > > > >> > > > >> > > > > > > >> > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > On Tue, Jan 2, 2018 at 6:28 PM,
>> > Jun
>> > > > Rao
>> > > > >> <
>> > > > >> > > > >> > > > j...@confluent.io
>> > > > >> > > > >> > > > > >
>> > > > >> > > > >> > > > > > > >> wrote:
>> > > > >> > > > >> > > > > > > >> > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > > Hi, Dong,
>> > > > >> > > > >> > > > > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > > Thanks for the reply.
>> > > > >> > > > >> > > > > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > > To solve the topic recreation
>> > > issue,
>> > > > >> we
>> > > > >> > > could
>> > > > >> > > > >> use
>> > > > >> > > > >> > > > > either a
>> > > > >> > > > >> > > > > > > >> global
>> > > > >> > > > >> > > > > > > >> > > > > > metadata
>> > > > >> > > > >> > > > > > > >> > > > > > > version or a partition level
>> > > epoch.
>> > > > >> But
>> > > > >> > > > either
>> > > > >> > > > >> one
>> > > > >> > > > >> > > > will
>> > > > >> > > > >> > > > > > be a
>> > > > >> > > > >> > > > > > > >> new
>> > > > >> > > > >> > > > > > > >> > > > > concept,
>> > > > >> > > > >> > > > > > > >> > > > > > > right? To me, the latter
>> seems
>> > > more
>> > > > >> > > natural.
>> > > > >> > > > It
>> > > > >> > > > >> > also
>> > > > >> > > > >> > > > > makes
>> > > > >> > > > >> > > > > > > it
>> > > > >> > > > >> > > > > > > >> > > easier
>> > > > >> > > > >> > > > > > > >> > > > to
>> > > > >> > > > >> > > > > > > >> > > > > > > detect if a consumer's
>> offset is
>> > > > still
>> > > > >> > > valid
>> > > > >> > > > >> > after a
>> > > > >> > > > >> > > > > topic
>> > > > >> > > > >> > > > > > > is
>> > > > >> > > > >> > > > > > > >> > > > > recreated.
>> > > > >> > > > >> > > > > > > >> > > > > > As
>> > > > >> > > > >> > > > > > > >> > > > > > > you pointed out, we don't
>> need
>> > to
>> > > > >> store
>> > > > >> > the
>> > > > >> > > > >> > > partition
>> > > > >> > > > >> > > > > > epoch
>> > > > >> > > > >> > > > > > > in
>> > > > >> > > > >> > > > > > > >> > the
>> > > > >> > > > >> > > > > > > >> > > > > > message.
>> > > > >> > > > >> > > > > > > >> > > > > > > The following is what I am
>> > > thinking.
>> > > > >> > When a
>> > > > >> > > > >> > > partition
>> > > > >> > > > >> > > > is
>> > > > >> > > > >> > > > > > > >> created,
>> > > > >> > > > >> > > > > > > >> > > we
>> > > > >> > > > >> > > > > > > >> > > > > can
>> > > > >> > > > >> > > > > > > >> > > > > > > assign a partition epoch
>> from an
>> > > > >> > > > >> ever-increasing
>> > > > >> > > > >> > > > global
>> > > > >> > > > >> > > > > > > >> counter
>> > > > >> > > > >> > > > > > > >> > and
>> > > > >> > > > >> > > > > > > >> > > > > store
>> > > > >> > > > >> > > > > > > >> > > > > > > it in
>> /brokers/topics/[topic]/
>> > > > >> > > > >> > > > partitions/[partitionId]
>> > > > >> > > > >> > > > > in
>> > > > >> > > > >> > > > > > > ZK.
>> > > > >> > > > >> > > > > > > >> > The
>> > > > >> > > > >> > > > > > > >> > > > > > > partition
>> > > > >> > > > >> > > > > > > >> > > > > > > epoch is propagated to every
>> > > broker.
>> > > > >> The
>> > > > >> > > > >> consumer
>> > > > >> > > > >> > > will
>> > > > >> > > > >> > > > > be
>> > > > >> > > > >> > > > > > > >> > tracking
>> > > > >> > > > >> > > > > > > >> > > a
>> > > > >> > > > >> > > > > > > >> > > > > > tuple
>> > > > >> > > > >> > > > > > > >> > > > > > > of <offset, leader epoch,
>> > > partition
>> > > > >> > epoch>
>> > > > >> > > > for
>> > > > >> > > > >> > > > offsets.
>> > > > >> > > > >> > > > > > If a
>> > > > >> > > > >> > > > > > > >> > topic
>> > > > >> > > > >> > > > > > > >> > > is
>> > > > >> > > > >> > > > > > > >> > > > > > > recreated, it's possible
>> that a
>> > > > >> > consumer's
>> > > > >> > > > >> offset
>> > > > >> > > > >> > > and
>> > > > >> > > > >> > > > > > leader
>> > > > >> > > > >> > > > > > > >> > epoch
>> > > > >> > > > >> > > > > > > >> > > > > still
>> > > > >> > > > >> > > > > > > >> > > > > > > match that in the broker, but
>> > > > >> partition
>> > > > >> > > epoch
>> > > > >> > > > >> > won't
>> > > > >> > > > >> > > > be.
>> > > > >> > > > >> > > > > In
>> > > > >> > > > >> > > > > > > >> this
>> > > > >> > > > >> > > > > > > >> > > case,
>> > > > >> > > > >> > > > > > > >> > > > > we
>> > > > >> > > > >> > > > > > > >> > > > > > > can potentially still treat
>> the
>> > > > >> > consumer's
>> > > > >> > > > >> offset
>> > > > >> > > > >> > as
>> > > > >> > > > >> > > > out
>> > > > >> > > > >> > > > > > of
>> > > > >> > > > >> > > > > > > >> range
>> > > > >> > > > >> > > > > > > >> > > and
>> > > > >> > > > >> > > > > > > >> > > > > > reset
>> > > > >> > > > >> > > > > > > >> > > > > > > the offset based on the
>> offset
>> > > reset
>> > > > >> > policy
>> > > > >> > > > in
>> > > > >> > > > >> the
>> > > > >> > > > >> > > > > > consumer.
>> > > > >> > > > >> > > > > > > >> This
>> > > > >> > > > >> > > > > > > >> > > > seems
>> > > > >> > > > >> > > > > > > >> > > > > > > harder to do with a global
>> > > metadata
>> > > > >> > > version.
>> > > > >> > > > >> > > > > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > > Jun
>> > > > >> > > > >> > > > > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > > On Mon, Dec 25, 2017 at 6:56
>> AM,
>> > > > Dong
>> > > > >> > Lin <
>> > > > >> > > > >> > > > > > > >> lindon...@gmail.com>
>> > > > >> > > > >> > > > > > > >> > > > wrote:
>> > > > >> > > > >> > > > > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > > > Hey Jun,
>> > > > >> > > > >> > > > > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > > > This is a very good
>> example.
>> > > After
>> > > > >> > > thinking
>> > > > >> > > > >> > > through
>> > > > >> > > > >> > > > > this
>> > > > >> > > > >> > > > > > > in
>> > > > >> > > > >> > > > > > > >> > > > detail, I
>> > > > >> > > > >> > > > > > > >> > > > > > > agree
>> > > > >> > > > >> > > > > > > >> > > > > > > > that we need to commit
>> offset
>> > > with
>> > > > >> > leader
>> > > > >> > > > >> epoch
>> > > > >> > > > >> > in
>> > > > >> > > > >> > > > > order
>> > > > >> > > > >> > > > > > > to
>> > > > >> > > > >> > > > > > > >> > > address
>> > > > >> > > > >> > > > > > > >> > > > > > this
>> > > > >> > > > >> > > > > > > >> > > > > > > > example.
>> > > > >> > > > >> > > > > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > > > I think the remaining
>> question
>> > > is
>> > > > >> how
>> > > > >> > to
>> > > > >> > > > >> address
>> > > > >> > > > >> > > the
>> > > > >> > > > >> > > > > > > >> scenario
>> > > > >> > > > >> > > > > > > >> > > that
>> > > > >> > > > >> > > > > > > >> > > > > the
>> > > > >> > > > >> > > > > > > >> > > > > > > > topic is deleted and
>> > re-created.
>> > > > One
>> > > > >> > > > possible
>> > > > >> > > > >> > > > solution
>> > > > >> > > > >> > > > > > is
>> > > > >> > > > >> > > > > > > to
>> > > > >> > > > >> > > > > > > >> > > commit
>> > > > >> > > > >> > > > > > > >> > > > > > > offset
>> > > > >> > > > >> > > > > > > >> > > > > > > > with both the leader epoch
>> and
>> > > the
>> > > > >> > > metadata
>> > > > >> > > > >> > > version.
>> > > > >> > > > >> > > > > The
>> > > > >> > > > >> > > > > > > >> logic
>> > > > >> > > > >> > > > > > > >> > > and
>> > > > >> > > > >> > > > > > > >> > > > > the
>> > > > >> > > > >> > > > > > > >> > > > > > > > implementation of this
>> > solution
>> > > > does
>> > > > >> > not
>> > > > >> > > > >> > require a
>> > > > >> > > > >> > > > new
>> > > > >> > > > >> > > > > > > >> concept
>> > > > >> > > > >> > > > > > > >> > > > (e.g.
>> > > > >> > > > >> > > > > > > >> > > > > > > > partition epoch) and it
>> does
>> > not
>> > > > >> > require
>> > > > >> > > > any
>> > > > >> > > > >> > > change
>> > > > >> > > > >> > > > to
>> > > > >> > > > >> > > > > > the
>> > > > >> > > > >> > > > > > > >> > > message
>> > > > >> > > > >> > > > > > > >> > > > > > format
>> > > > >> > > > >> > > > > > > >> > > > > > > > or leader epoch. It also
>> > allows
>> > > us
>> > > > >> to
>> > > > >> > > order
>> > > > >> > > > >> the
>> > > > >> > > > >> > > > > metadata
>> > > > >> > > > >> > > > > > > in
>> > > > >> > > > >> > > > > > > >> a
>> > > > >> > > > >> > > > > > > >> > > > > > > > straightforward manner
>> which
>> > may
>> > > > be
>> > > > >> > > useful
>> > > > >> > > > in
>> > > > >> > > > >> > the
>> > > > >> > > > >> > > > > > future.
>> > > > >> > > > >> > > > > > > >> So it
>> > > > >> > > > >> > > > > > > >> > > may
>> > > > >> > > > >> > > > > > > >> > > > > be
>> > > > >> > > > >> > > > > > > >> > > > > > a
>> > > > >> > > > >> > > > > > > >> > > > > > > > better solution than
>> > generating
>> > > a
>> > > > >> > random
>> > > > >> > > > >> > partition
>> > > > >> > > > >> > > > > epoch
>> > > > >> > > > >> > > > > > > >> every
>> > > > >> > > > >> > > > > > > >> > > time
>> > > > >> > > > >> > > > > > > >> > > > > we
>> > > > >> > > > >> > > > > > > >> > > > > > > > create a partition. Does
>> this
>> > > > sound
>> > > > >> > > > >> reasonable?
>> > > > >> > > > >> > > > > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > > > Previously one concern with
>> > > using
>> > > > >> the
>> > > > >> > > > >> metadata
>> > > > >> > > > >> > > > version
>> > > > >> > > > >> > > > > > is
>> > > > >> > > > >> > > > > > > >> that
>> > > > >> > > > >> > > > > > > >> > > > > consumer
>> > > > >> > > > >> > > > > > > >> > > > > > > > will be forced to refresh
>> > > metadata
>> > > > >> even
>> > > > >> > > if
>> > > > >> > > > >> > > metadata
>> > > > >> > > > >> > > > > > > version
>> > > > >> > > > >> > > > > > > >> is
>> > > > >> > > > >> > > > > > > >> > > > > > increased
>> > > > >> > > > >> > > > > > > >> > > > > > > > due to topics that the
>> > consumer
>> > > is
>> > > > >> not
>> > > > >> > > > >> > interested
>> > > > >> > > > >> > > > in.
>> > > > >> > > > >> > > > > > Now
>> > > > >> > > > >> > > > > > > I
>> > > > >> > > > >> > > > > > > >> > > > realized
>> > > > >> > > > >> > > > > > > >> > > > > > that
>> > > > >> > > > >> > > > > > > >> > > > > > > > this is probably not a
>> > problem.
>> > > > >> > Currently
>> > > > >> > > > >> client
>> > > > >> > > > >> > > > will
>> > > > >> > > > >> > > > > > > >> refresh
>> > > > >> > > > >> > > > > > > >> > > > > metadata
>> > > > >> > > > >> > > > > > > >> > > > > > > > either due to
>> > > > >> InvalidMetadataException
>> > > > >> > in
>> > > > >> > > > the
>> > > > >> > > > >> > > > response
>> > > > >> > > > >> > > > > > > from
>> > > > >> > > > >> > > > > > > >> > > broker
>> > > > >> > > > >> > > > > > > >> > > > or
>> > > > >> > > > >> > > > > > > >> > > > > > due
>> > > > >> > > > >> > > > > > > >> > > > > > > > to metadata expiry. The
>> > addition
>> > > > of
>> > > > >> the
>> > > > >> > > > >> metadata
>> > > > >> > > > >> > > > > version
>> > > > >> > > > >> > > > > > > >> should
>> > > > >> > > > >> > > > > > > >> > > > > > increase
>> > > > >> > > > >> > > > > > > >> > > > > > > > the overhead of metadata
>> > refresh
>> > > > >> caused
>> > > > >> > > by
>> > > > >> > > > >> > > > > > > >> > > > InvalidMetadataException.
>> > > > >> > > > >> > > > > > > >> > > > > If
>> > > > >> > > > >> > > > > > > >> > > > > > > > client refresh metadata
>> due to
>> > > > >> expiry
>> > > > >> > and
>> > > > >> > > > it
>> > > > >> > > > >> > > > receives
>> > > > >> > > > >> > > > > a
>> > > > >> > > > >> > > > > > > >> > metadata
>> > > > >> > > > >> > > > > > > >> > > > > whose
>> > > > >> > > > >> > > > > > > >> > > > > > > > version is lower than the
>> > > current
>> > > > >> > > metadata
>> > > > >> > > > >> > > version,
>> > > > >> > > > >> > > > we
>> > > > >> > > > >> > > > > > can
>> > > > >> > > > >> > > > > > > >> > reject
>> > > > >> > > > >> > > > > > > >> > > > the
>> > > > >> > > > >> > > > > > > >> > > > > > > > metadata but still reset
>> the
>> > > > >> metadata
>> > > > >> > > age,
>> > > > >> > > > >> which
>> > > > >> > > > >> > > > > > > essentially
>> > > > >> > > > >> > > > > > > >> > keep
>> > > > >> > > > >> > > > > > > >> > > > the
>> > > > >> > > > >> > > > > > > >> > > > > > > > existing behavior in the
>> > client.
>> > > > >> > > > >> > > > > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > > > Thanks much,
>> > > > >> > > > >> > > > > > > >> > > > > > > > Dong
>> > > > >> > > > >> > > > > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > > >
>> > > > >> > > > >> > > > > > > >> > > > > >
>> > > > >> > > > >> > > > > > > >> > > > >
>> > > > >> > > > >> > > > > > > >> > > >
>> > > > >> > > > >> > > > > > > >> > >
>> > > > >> > > > >> > > > > > > >> >
>> > > > >> > > > >> > > > > > > >>
>> > > > >> > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > > >
>> > > > >> > > > >> > > > > > >
>> > > > >> > > > >> > > > > >
>> > > > >> > > > >> > > > >
>> > > > >> > > > >> > > >
>> > > > >> > > > >> > >
>> > > > >> > > > >> >
>> > > > >> > > > >>
>> > > > >> > > > >
>> > > > >> > > > >
>> > > > >> > > >
>> > > > >> > >
>> > > > >> >
>> > > > >>
>> > > > >
>> > > > >
>> > > >
>> > >
>> >
>>
>
>
