Hey Jun, Jason,
Thanks much for all the review! I will open the voting thread.
Regards,
Dong
On Tue, Jan 23, 2018 at 3:37 PM, Jun Rao <j...@confluent.io> wrote:
> Hi, Dong,
>
> The current KIP looks good to me.
>
> Thanks,
>
> Jun
>
> On Tue, Jan 23, 2018 at 12:29 PM, Dong Lin <lindon...@gmail.com> wrote:
>
> > 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
> > >> > > > >> > > > >> > > > > > > >> > > > > > > >
> > >> > > > >> > > > >> > > > > > > >> > > > > > >
> > >> > > > >> > > > >> > > > > > > >> > > > > >
> > >> > > > >> > > > >> > > > > > > >> > > > >
> > >> > > > >> > > > >> > > > > > > >> > > >
> > >> > > > >> > > > >> > > > > > > >> > >
> > >> > > > >> > > > >> > > > > > > >> >
> > >> > > > >> > > > >> > > > > > > >>
> > >> > > > >> > > > >> > > > > > > >
> > >> > > > >> > > > >> > > > > > > >
> > >> > > > >> > > > >> > > > > > >
> > >> > > > >> > > > >> > > > > >
> > >> > > > >> > > > >> > > > >
> > >> > > > >> > > > >> > > >
> > >> > > > >> > > > >> > >
> > >> > > > >> > > > >> >
> > >> > > > >> > > > >>
> > >> > > > >> > > > >
> > >> > > > >> > > > >
> > >> > > > >> > > >
> > >> > > > >> > >
> > >> > > > >> >
> > >> > > > >>
> > >> > > > >
> > >> > > > >
> > >> > > >
> > >> > >
> > >> >
> > >>
> > >
> > >
> >
>
