Hi, Calvin and Justine,
Historically, when we change the record format in the log, we don't support
software version downgrading.
For the record format change in the metadata log, have we thought about
forcing the write of the latest metadata records with the old version
during MV downgrading? This will in theory allow the old version of the
software to obtain the latest metadata.
Thanks,
Jun
On Wed, Oct 4, 2023 at 9:53 AM Justine Olshan <jols...@confluent.io.invalid>
wrote:
> Sorry -- not MV but software version.
>
> On Wed, Oct 4, 2023 at 9:51 AM Justine Olshan <jols...@confluent.io>
> wrote:
>
> > Catching up with this discussion.
> >
> > I was just curious -- have we had other instances where downgrading MV is
> > not supported? I think Kafka typically tries to support downgrades, and I
> > couldn't think of other examples.
> >
> > Thanks,
> > Justine
> >
> > On Wed, Oct 4, 2023 at 9:40 AM Calvin Liu <ca...@confluent.io.invalid>
> > wrote:
> >
> >> Hi Jun,
> >> 54. Marked the software downgrading is not supported. As the old
> >> controller
> >> will not understand the new PartitionRecord and PartitionChangeRecord.
> >> Thanks!
> >>
> >> On Wed, Oct 4, 2023 at 9:12 AM Jun Rao <j...@confluent.io.invalid>
> wrote:
> >>
> >> > Hi, Calvin,
> >> >
> >> > Thanks for the reply. Just one more comment.
> >> >
> >> > 54. It seems that downgrading MV is supported. Is downgrading the
> >> software
> >> > version supported? It would be useful to document that.
> >> >
> >> > Thanks,
> >> >
> >> > Jun
> >> >
> >> > On Tue, Oct 3, 2023 at 4:55 PM Artem Livshits
> >> > <alivsh...@confluent.io.invalid> wrote:
> >> >
> >> > > Hi Colin,
> >> > >
> >> > > I think in your example "do_unclean_recovery" would need to do
> >> different
> >> > > things depending on the strategy.
> >> > >
> >> > > do_unclean_recovery() {
> >> > > if (unclean.recovery.manager.enabled) {
> >> > > if (strategy == Aggressive)
> >> > > use UncleanRecoveryManager(waitLastKnownERL=false) // just
> >> inspect
> >> > > logs from whoever is available
> >> > > else
> >> > > use UncleanRecoveryManager(waitLastKnownERL=true) // must
> wait
> >> > for
> >> > > at least last known ELR
> >> > > } else {
> >> > > if (strategy == Aggressive)
> >> > > choose the last known leader if that is available, or a random
> >> > leader
> >> > > if not)
> >> > > else
> >> > > wait for last known leader to get back
> >> > > }
> >> > > }
> >> > >
> >> > > The idea is that the Aggressive strategy would kick in as soon as we
> >> lost
> >> > > the leader and would pick a leader from whoever is available; but
> the
> >> > > Balanced will only kick in when ELR is empty and will wait for the
> >> > brokers
> >> > > that likely have most data to be available.
> >> > >
> >> > > On Tue, Oct 3, 2023 at 3:04 PM Colin McCabe <cmcc...@apache.org>
> >> wrote:
> >> > >
> >> > > > On Tue, Oct 3, 2023, at 10:49, Jun Rao wrote:
> >> > > > > Hi, Calvin,
> >> > > > >
> >> > > > > Thanks for the update KIP. A few more comments.
> >> > > > >
> >> > > > > 41. Why would a user choose the option to select a random
> replica
> >> as
> >> > > the
> >> > > > > leader instead of using unclean.recovery.strateg=Aggressive? It
> >> seems
> >> > > > that
> >> > > > > the latter is strictly better? If that's not the case, could we
> >> fold
> >> > > this
> >> > > > > option under unclean.recovery.strategy instead of introducing a
> >> > > separate
> >> > > > > config?
> >> > > >
> >> > > > Hi Jun,
> >> > > >
> >> > > > I thought the flow of control was:
> >> > > >
> >> > > > If there is no leader for the partition {
> >> > > > If (there are unfenced ELR members) {
> >> > > > choose_an_unfenced_ELR_member
> >> > > > } else if (there are fenced ELR members AND
> strategy=Aggressive) {
> >> > > > do_unclean_recovery
> >> > > > } else if (there are no ELR members AND strategy != None) {
> >> > > > do_unclean_recovery
> >> > > > } else {
> >> > > > do nothing about the missing leader
> >> > > > }
> >> > > > }
> >> > > >
> >> > > > do_unclean_recovery() {
> >> > > > if (unclean.recovery.manager.enabled) {
> >> > > > use UncleanRecoveryManager
> >> > > > } else {
> >> > > > choose the last known leader if that is available, or a random
> >> > leader
> >> > > > if not)
> >> > > > }
> >> > > > }
> >> > > >
> >> > > > However, I think this could be clarified, especially the behavior
> >> when
> >> > > > unclean.recovery.manager.enabled=false. Inuitively the goal for
> >> > > > unclean.recovery.manager.enabled=false is to be "the same as now,
> >> > mostly"
> >> > > > but it's very underspecified in the KIP, I agree.
> >> > > >
> >> > > > >
> >> > > > > 50. ElectLeadersRequest: "If more than 20 topics are included,
> >> only
> >> > the
> >> > > > > first 20 will be served. Others will be returned with
> >> > DesiredLeaders."
> >> > > > Hmm,
> >> > > > > not sure that I understand this. ElectLeadersResponse doesn't
> >> have a
> >> > > > > DesiredLeaders field.
> >> > > > >
> >> > > > > 51. GetReplicaLogInfo: "If more than 2000 partitions are
> included,
> >> > only
> >> > > > the
> >> > > > > first 2000 will be served" Do we return an error for the
> remaining
> >> > > > > partitions? Actually, should we include an errorCode field at
> the
> >> > > > partition
> >> > > > > level in GetReplicaLogInfoResponse to cover non-existing
> >> partitions
> >> > and
> >> > > > no
> >> > > > > authorization, etc?
> >> > > > >
> >> > > > > 52. The entry should matches => The entry should match
> >> > > > >
> >> > > > > 53. ElectLeadersRequest.DesiredLeaders: Should it be nullable
> >> since a
> >> > > > user
> >> > > > > may not specify DesiredLeaders?
> >> > > > >
> >> > > > > 54. Downgrade: Is that indeed possible? I thought earlier you
> said
> >> > that
> >> > > > > once the new version of the records are in the metadata log, one
> >> > can't
> >> > > > > downgrade since the old broker doesn't know how to parse the new
> >> > > version
> >> > > > of
> >> > > > > the metadata records?
> >> > > > >
> >> > > >
> >> > > > MetadataVersion downgrade is currently broken but we have fixing
> it
> >> on
> >> > > our
> >> > > > plate for Kafka 3.7.
> >> > > >
> >> > > > The way downgrade works is that "new features" are dropped,
> leaving
> >> > only
> >> > > > the old ones.
> >> > > >
> >> > > > > 55. CleanShutdownFile: Should we add a version field for future
> >> > > > extension?
> >> > > > >
> >> > > > > 56. Config changes are public facing. Could we have a separate
> >> > section
> >> > > to
> >> > > > > document all the config changes?
> >> > > >
> >> > > > +1. A separate section for this would be good.
> >> > > >
> >> > > > best,
> >> > > > Colin
> >> > > >
> >> > > > >
> >> > > > > Thanks,
> >> > > > >
> >> > > > > Jun
> >> > > > >
> >> > > > > On Mon, Sep 25, 2023 at 4:29 PM Calvin Liu
> >> > <ca...@confluent.io.invalid
> >> > > >
> >> > > > > wrote:
> >> > > > >
> >> > > > >> Hi Jun
> >> > > > >> Thanks for the comments.
> >> > > > >>
> >> > > > >> 40. If we change to None, it is not guaranteed for no data
> loss.
> >> For
> >> > > > users
> >> > > > >> who are not able to validate the data with external resources,
> >> > manual
> >> > > > >> intervention does not give a better result but a loss of
> >> > availability.
> >> > > > So
> >> > > > >> practically speaking, the Balance mode would be a better
> default
> >> > > value.
> >> > > > >>
> >> > > > >> 41. No, it represents how we want to do the unclean leader
> >> election.
> >> > > If
> >> > > > it
> >> > > > >> is false, the unclean leader election will be the old random
> way.
> >> > > > >> Otherwise, the unclean recovery will be used.
> >> > > > >>
> >> > > > >> 42. Good catch. Updated.
> >> > > > >>
> >> > > > >> 43. Only the first 20 topics will be served. Others will be
> >> returned
> >> > > > with
> >> > > > >> InvalidRequestError
> >> > > > >>
> >> > > > >> 44. The order matters. The desired leader entries match with
> the
> >> > topic
> >> > > > >> partition list by the index.
> >> > > > >>
> >> > > > >> 45. Thanks! Updated.
> >> > > > >>
> >> > > > >> 46. Good advice! Updated.
> >> > > > >>
> >> > > > >> 47.1, updated the comment. Basically it will elect the replica
> in
> >> > the
> >> > > > >> desiredLeader field to be the leader
> >> > > > >>
> >> > > > >> 47.2 We can let the admin client do the conversion. Using the
> >> > > > desiredLeader
> >> > > > >> field in the json format seems easier for users.
> >> > > > >>
> >> > > > >> 48. Once the MV version is downgraded, all the ELR related
> fields
> >> > will
> >> > > > be
> >> > > > >> removed on the next partition change. The controller will also
> >> > ignore
> >> > > > the
> >> > > > >> ELR fields. Updated the KIP.
> >> > > > >>
> >> > > > >> 49. Yes, it would be deprecated/removed.
> >> > > > >>
> >> > > > >>
> >> > > > >> On Mon, Sep 25, 2023 at 3:49 PM Jun Rao
> <j...@confluent.io.invalid
> >> >
> >> > > > wrote:
> >> > > > >>
> >> > > > >> > Hi, Calvin,
> >> > > > >> >
> >> > > > >> > Thanks for the updated KIP. Made another pass. A few more
> >> comments
> >> > > > below.
> >> > > > >> >
> >> > > > >> > 40. unclean.leader.election.enable.false ->
> >> > > > >> > unclean.recovery.strategy.Balanced: The Balanced mode could
> >> still
> >> > > > lead to
> >> > > > >> > data loss. So, I am wondering if
> >> > > unclean.leader.election.enable.false
> >> > > > >> > should map to None?
> >> > > > >> >
> >> > > > >> > 41. unclean.recovery.manager.enabled: I am not sure why we
> >> > introduce
> >> > > > this
> >> > > > >> > additional config. Is it the same as
> >> > unclean.recovery.strategy=None?
> >> > > > >> >
> >> > > > >> > 42. DescribeTopicResponse.TopicAuthorizedOperations: Should
> >> this
> >> > be
> >> > > at
> >> > > > >> the
> >> > > > >> > topic level?
> >> > > > >> >
> >> > > > >> > 43. "Limit: 20 topics max per request": Could we describe
> what
> >> > > > happens if
> >> > > > >> > the request includes more than 20 topics?
> >> > > > >> >
> >> > > > >> > 44. ElectLeadersRequest.DesiredLeaders: Could we describe
> >> whether
> >> > > the
> >> > > > >> > ordering matters?
> >> > > > >> >
> >> > > > >> > 45. GetReplicaLogInfo.TopicPartitions: "about": "The topic
> >> > > partitions
> >> > > > to
> >> > > > >> > elect leaders.": The description in "about" is incorrect.
> >> > > > >> >
> >> > > > >> > 46. GetReplicaLogInfoResponse: Should we nest partitions
> under
> >> > > > topicId to
> >> > > > >> > be consistent with other types of responses?
> >> > > > >> >
> >> > > > >> > 47. kafka-leader-election.sh:
> >> > > > >> > 47.1 Could we explain DESIGNATION?
> >> > > > >> > 47.2 desiredLeader: Should it be a list to match the field in
> >> > > > >> > ElectLeadersRequest?
> >> > > > >> >
> >> > > > >> > 48. We could add a section on downgrade?
> >> > > > >> >
> >> > > > >> > 49. LastKnownLeader: This seems only needed in the first
> phase
> >> of
> >> > > > >> > delivering ELR. Will it be removed when the complete KIP is
> >> > > delivered?
> >> > > > >> >
> >> > > > >> > Thanks,
> >> > > > >> >
> >> > > > >> > Jun
> >> > > > >> >
> >> > > > >> > On Tue, Sep 19, 2023 at 1:30 PM Colin McCabe <
> >> cmcc...@apache.org>
> >> > > > wrote:
> >> > > > >> >
> >> > > > >> > > Hi Calvin,
> >> > > > >> > >
> >> > > > >> > > Thanks for the explanations. I like the idea of using none,
> >> > > > balanced,
> >> > > > >> > > aggressive. We also had an offline discussion about why it
> is
> >> > good
> >> > > > to
> >> > > > >> > use a
> >> > > > >> > > new config key (basically, so that we can deprecate the old
> >> one
> >> > > > which
> >> > > > >> had
> >> > > > >> > > only false/true values in 4.0) With these changes, I am +1.
> >> > > > >> > >
> >> > > > >> > > best,
> >> > > > >> > > Colin
> >> > > > >> > >
> >> > > > >> > > On Mon, Sep 18, 2023, at 15:54, Calvin Liu wrote:
> >> > > > >> > > > Hi Colin,
> >> > > > >> > > > Also, can we deprecate unclean.leader.election.enable in
> >> 4.0?
> >> > > > Before
> >> > > > >> > > that,
> >> > > > >> > > > we can have both the config unclean.recovery.strategy and
> >> > > > >> > > > unclean.leader.election.enable
> >> > > > >> > > > and using the unclean.recovery.Enabled to determine which
> >> > config
> >> > > > to
> >> > > > >> use
> >> > > > >> > > > during the unclean leader election.
> >> > > > >> > > >
> >> > > > >> > > > On Mon, Sep 18, 2023 at 3:51 PM Calvin Liu <
> >> > ca...@confluent.io>
> >> > > > >> wrote:
> >> > > > >> > > >
> >> > > > >> > > >> Hi Colin,
> >> > > > >> > > >> For the unclean.recovery.strategy config name, how about
> >> we
> >> > use
> >> > > > the
> >> > > > >> > > >> following
> >> > > > >> > > >> None. It basically means no unclean recovery will be
> >> > performed.
> >> > > > >> > > >> Aggressive. It means availability goes first. Whenever
> the
> >> > > > partition
> >> > > > >> > > can't
> >> > > > >> > > >> elect a durable replica, the controller will try the
> >> unclean
> >> > > > >> recovery.
> >> > > > >> > > >> Balanced. It is the balance point of the availability
> >> > > > >> > first(Aggressive)
> >> > > > >> > > >> and least availability(None). The controller performs
> >> unclean
> >> > > > >> recovery
> >> > > > >> > > when
> >> > > > >> > > >> both ISR and ELR are empty.
> >> > > > >> > > >>
> >> > > > >> > > >>
> >> > > > >> > > >> On Fri, Sep 15, 2023 at 11:42 AM Calvin Liu <
> >> > > ca...@confluent.io>
> >> > > > >> > wrote:
> >> > > > >> > > >>
> >> > > > >> > > >>> Hi Colin,
> >> > > > >> > > >>>
> >> > > > >> > > >>> > So, the proposal is that if someone sets
> >> > > > >> > > "unclean.leader.election.enable
> >> > > > >> > > >>> = true"...
> >> > > > >> > > >>>
> >> > > > >> > > >>>
> >> > > > >> > > >>> The idea is to use one of the
> >> unclean.leader.election.enable
> >> > > and
> >> > > > >> > > >>> unclean.recovery.strategy based on the
> >> > > > unclean.recovery.Enabled. A
> >> > > > >> > > possible
> >> > > > >> > > >>> version can be
> >> > > > >> > > >>>
> >> > > > >> > > >>> If unclean.recovery.Enabled:
> >> > > > >> > > >>>
> >> > > > >> > > >>> {
> >> > > > >> > > >>>
> >> > > > >> > > >>> Check unclean.recovery.strategy. If set, use it.
> >> Otherwise,
> >> > > > check
> >> > > > >> > > >>> unclean.leader.election.enable and translate it to
> >> > > > >> > > >>> unclean.recovery.strategy.
> >> > > > >> > > >>>
> >> > > > >> > > >>> } else {
> >> > > > >> > > >>>
> >> > > > >> > > >>> Use unclean.leader.election.enable
> >> > > > >> > > >>>
> >> > > > >> > > >>> }
> >> > > > >> > > >>>
> >> > > > >> > > >>>
> >> > > > >> > > >>> —--------
> >> > > > >> > > >>>
> >> > > > >> > > >>> >The configuration key should be
> >> > > > >> "unclean.recovery.manager.enabled",
> >> > > > >> > > >>> right?
> >> > > > >> > > >>>
> >> > > > >> > > >>>
> >> > > > >> > > >>> I think we have two ways of choosing a leader
> uncleanly,
> >> > > unclean
> >> > > > >> > leader
> >> > > > >> > > >>> election and unclean recovery(log inspection) and we
> try
> >> to
> >> > > > switch
> >> > > > >> > > between
> >> > > > >> > > >>> them.
> >> > > > >> > > >>>
> >> > > > >> > > >>> Do you mean we want to develop two ways of performing
> the
> >> > > > unclean
> >> > > > >> > > >>> recovery and one of them is using “unclean recovery
> >> > manager”?
> >> > > I
> >> > > > >> guess
> >> > > > >> > > we
> >> > > > >> > > >>> haven’t discussed the second way.
> >> > > > >> > > >>>
> >> > > > >> > > >>>
> >> > > > >> > > >>> —-------
> >> > > > >> > > >>>
> >> > > > >> > > >>> >How do these 4 levels of overrides interact with your
> >> new
> >> > > > >> > > >>> configurations?
> >> > > > >> > > >>>
> >> > > > >> > > >>>
> >> > > > >> > > >>> I do notice in the Kraft controller code, the method to
> >> > check
> >> > > > >> whether
> >> > > > >> > > >>> perform unclean leader election is hard coded to false
> >> since
> >> > > > >> > > >>> 2021(uncleanLeaderElectionEnabledForTopic). Isn’t it a
> >> good
> >> > > > chance
> >> > > > >> to
> >> > > > >> > > >>> completely deprecate the
> unclean.leader.election.enable?
> >> We
> >> > > > don’t
> >> > > > >> > even
> >> > > > >> > > have
> >> > > > >> > > >>> to worry about the config conversion.
> >> > > > >> > > >>>
> >> > > > >> > > >>> On the other hand, whatever the override is, as long as
> >> the
> >> > > > >> > controller
> >> > > > >> > > >>> can have the final effective
> >> unclean.leader.election.enable,
> >> > > the
> >> > > > >> > topic
> >> > > > >> > > >>> level config unclean.recovery.strategy, the cluster
> level
> >> > > config
> >> > > > >> > > >>> unclean.recovery.Enabled, the controller can calculate
> >> the
> >> > > > correct
> >> > > > >> > > methods
> >> > > > >> > > >>> to use right?
> >> > > > >> > > >>>
> >> > > > >> > > >>>
> >> > > > >> > > >>> On Fri, Sep 15, 2023 at 10:02 AM Colin McCabe <
> >> > > > cmcc...@apache.org>
> >> > > > >> > > wrote:
> >> > > > >> > > >>>
> >> > > > >> > > >>>> On Thu, Sep 14, 2023, at 22:23, Calvin Liu wrote:
> >> > > > >> > > >>>> > Hi Colin
> >> > > > >> > > >>>> > 1. I think using the new config name is more clear.
> >> > > > >> > > >>>> > a. The unclean leader election is actually
> >> removed
> >> > > if
> >> > > > >> > unclean
> >> > > > >> > > >>>> > recovery is in use.
> >> > > > >> > > >>>> > b. Using multiple values in
> >> > > > >> unclean.leader.election.enable
> >> > > > >> > is
> >> > > > >> > > >>>> > confusing and it will be more confusing after people
> >> > forget
> >> > > > >> about
> >> > > > >> > > this
> >> > > > >> > > >>>> > discussion.
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> Hi Calvin,
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> So, the proposal is that if someone sets
> >> > > > >> > > "unclean.leader.election.enable
> >> > > > >> > > >>>> = true" but then sets one of your new configurations,
> >> the
> >> > > > value of
> >> > > > >> > > >>>> unclean.leader.election.enable is ignored? That seems
> >> less
> >> > > > clear
> >> > > > >> to
> >> > > > >> > > me, not
> >> > > > >> > > >>>> more. Just in general, having multiple configuration
> >> keys
> >> > to
> >> > > > >> control
> >> > > > >> > > the
> >> > > > >> > > >>>> same thing confuses users. Basically, they are sitting
> >> at a
> >> > > > giant
> >> > > > >> > > control
> >> > > > >> > > >>>> panel, and some of the levers do nothing.
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> > 2. Sorry I forgot to mention in the response that I
> >> did
> >> > add
> >> > > > the
> >> > > > >> > > >>>> > unclean.recovery.Enabled flag.
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> The configuration key should be
> >> > > > >> "unclean.recovery.manager.enabled",
> >> > > > >> > > >>>> right? Becuase we can do "unclean recovery" without
> the
> >> > > > manager.
> >> > > > >> > > Disabling
> >> > > > >> > > >>>> the manager just means we use a different mechanism
> for
> >> > > > recovery.
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> > c. Maybe I underestimated the challenge of
> >> > replacing
> >> > > > the
> >> > > > >> > > >>>> config. Any
> >> > > > >> > > >>>> > implementation problems ahead?
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> There are four levels of overrides for
> >> > > > >> > unclean.leader.election.enable.
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> 1. static configuration for node.
> >> > > > >> > > >>>> This goes in the configuration file, typically
> named
> >> > > > >> > > >>>> server.properties
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> 2. dynamic configuration for node default
> >> > > > >> > > >>>> ConfigResource(type=BROKER, name="")
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> 3. dynamic configuration for node
> >> > > > >> > > >>>> ConfigResource(type=BROKER, name=<controller id>)
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> 4. dynamic configuration for topic
> >> > > > >> > > >>>> ConfigResource(type=TOPIC, name=<topic-name>)
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> How do these 4 levels of overrides interact with your
> >> new
> >> > > > >> > > >>>> configurations? If the new configurations dominate
> over
> >> the
> >> > > old
> >> > > > >> > ones,
> >> > > > >> > > it
> >> > > > >> > > >>>> seems like this will get a lot more confusing to
> >> implement
> >> > > (and
> >> > > > >> also
> >> > > > >> > > to
> >> > > > >> > > >>>> use.)
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> Again, I'd recommend just adding some new values to
> >> > > > >> > > >>>> unclean.leader.election.enable. It's simple and will
> >> > prevent
> >> > > > user
> >> > > > >> > > confusion
> >> > > > >> > > >>>> (as well as developer confusion.)
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> best,
> >> > > > >> > > >>>> Colin
> >> > > > >> > > >>>>
> >> > > > >> > > >>>>
> >> > > > >> > > >>>> > 3. About the admin client, I mentioned 3 changes in
> >> the
> >> > > > client.
> >> > > > >> > > >>>> Anything
> >> > > > >> > > >>>> > else I missed in the KIP?
> >> > > > >> > > >>>> > a. The client will switch to using the new RPC
> >> > > instead
> >> > > > of
> >> > > > >> > > >>>> > MetadataRequest for the topics.
> >> > > > >> > > >>>> > b. The TopicPartitionInfo used in
> >> TopicDescription
> >> > > > needs
> >> > > > >> to
> >> > > > >> > > add
> >> > > > >> > > >>>> new
> >> > > > >> > > >>>> > fields related to the ELR.
> >> > > > >> > > >>>> > c. The outputs will add the ELR related
> fields.
> >> > > > >> > > >>>> >
> >> > > > >> > > >>>> > On Thu, Sep 14, 2023 at 9:19 PM Colin McCabe <
> >> > > > >> cmcc...@apache.org>
> >> > > > >> > > >>>> wrote:
> >> > > > >> > > >>>> >
> >> > > > >> > > >>>> >> Hi Calvin,
> >> > > > >> > > >>>> >>
> >> > > > >> > > >>>> >> Thanks for the changes.
> >> > > > >> > > >>>> >>
> >> > > > >> > > >>>> >> 1. Earlier I commented that creating
> >> > > > >> "unclean.recovery.strategy "
> >> > > > >> > > is
> >> > > > >> > > >>>> not
> >> > > > >> > > >>>> >> necessary, and we can just reuse the existing
> >> > > > >> > > >>>> >> "unclean.leader.election.enable" configuration key.
> >> > Let's
> >> > > > >> discuss
> >> > > > >> > > >>>> that.
> >> > > > >> > > >>>> >>
> >> > > > >> > > >>>> >> 2.I also don't understand why you didn't add a
> >> > > > configuration to
> >> > > > >> > > >>>> enable or
> >> > > > >> > > >>>> >> disable the Unclean Recovery Manager. This seems
> >> like a
> >> > > very
> >> > > > >> > simple
> >> > > > >> > > >>>> way to
> >> > > > >> > > >>>> >> handle the staging issue which we discussed. The
> URM
> >> can
> >> > > > just
> >> > > > >> be
> >> > > > >> > > >>>> turned off
> >> > > > >> > > >>>> >> until it is production ready. Let's discuss this.
> >> > > > >> > > >>>> >>
> >> > > > >> > > >>>> >> 3. You still need to describe the changes to
> >> AdminClient
> >> > > > that
> >> > > > >> are
> >> > > > >> > > >>>> needed
> >> > > > >> > > >>>> >> to use DescribeTopicRequest.
> >> > > > >> > > >>>> >>
> >> > > > >> > > >>>> >> Keep at it. It's looking better. :)
> >> > > > >> > > >>>> >>
> >> > > > >> > > >>>> >> best,
> >> > > > >> > > >>>> >> Colin
> >> > > > >> > > >>>> >>
> >> > > > >> > > >>>> >>
> >> > > > >> > > >>>> >> On Thu, Sep 14, 2023, at 11:03, Calvin Liu wrote:
> >> > > > >> > > >>>> >> > Hi Colin
> >> > > > >> > > >>>> >> > Thanks for the comments!
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > I did the following changes
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > 1.
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > Simplified the API spec section to only
> include
> >> the
> >> > > > diff.
> >> > > > >> > > >>>> >> > 2.
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > Reordered the HWM requirement section.
> >> > > > >> > > >>>> >> > 3.
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > Removed the URM implementation details to keep
> >> the
> >> > > > >> necessary
> >> > > > >> > > >>>> >> > characteristics to perform the unclean
> recovery.
> >> > > > >> > > >>>> >> > 1.
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > When to perform the unclean recovery
> >> > > > >> > > >>>> >> > 2.
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > Under different config, how the unclean
> >> recovery
> >> > > > finds
> >> > > > >> > the
> >> > > > >> > > >>>> leader.
> >> > > > >> > > >>>> >> > 3.
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > How the config
> unclean.leader.election.enable
> >> > and
> >> > > > >> > > >>>> >> > unclean.recovery.strategy are converted
> when
> >> > users
> >> > > > >> > > >>>> enable/disable
> >> > > > >> > > >>>> >> the
> >> > > > >> > > >>>> >> > unclean recovery.
> >> > > > >> > > >>>> >> > 4.
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > More details about how we change admin client.
> >> > > > >> > > >>>> >> > 5.
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > API limits on the GetReplicaLogInfoRequest and
> >> > > > >> > > >>>> DescribeTopicRequest.
> >> > > > >> > > >>>> >> > 6.
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > Two metrics added
> >> > > > >> > > >>>> >> > 1.
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> >
> >> > > > Kafka.controller.global_under_min_isr_partition_count
> >> > > > >> > > >>>> >> > 2.
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> >
> >> kafka.controller.unclean_recovery_finished_count
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> > On Wed, Sep 13, 2023 at 10:46 AM Colin McCabe <
> >> > > > >> > > cmcc...@apache.org>
> >> > > > >> > > >>>> >> wrote:
> >> > > > >> > > >>>> >> >
> >> > > > >> > > >>>> >> >> On Tue, Sep 12, 2023, at 17:21, Calvin Liu
> wrote:
> >> > > > >> > > >>>> >> >> > Hi Colin
> >> > > > >> > > >>>> >> >> > Thanks for the comments!
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> Hi Calvin,
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> Thanks again for the KIP.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> One meta-comment: it's usually better to just
> do a
> >> > diff
> >> > > > on a
> >> > > > >> > > >>>> message
> >> > > > >> > > >>>> >> spec
> >> > > > >> > > >>>> >> >> file or java file if you're including changes to
> >> it
> >> > in
> >> > > > the
> >> > > > >> > KIP.
> >> > > > >> > > >>>> This is
> >> > > > >> > > >>>> >> >> easier to read than looking for "new fields
> begin"
> >> > etc.
> >> > > > in
> >> > > > >> the
> >> > > > >> > > >>>> text, and
> >> > > > >> > > >>>> >> >> gracefully handles the case where existing
> fields
> >> > were
> >> > > > >> > changed.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> > Rewrite the Additional High Watermark
> >> advancement
> >> > > > >> > requirement
> >> > > > >> > > >>>> >> >> > There was feedback on this section that some
> >> > readers
> >> > > > may
> >> > > > >> not
> >> > > > >> > > be
> >> > > > >> > > >>>> >> familiar
> >> > > > >> > > >>>> >> >> > with HWM and Ack=0,1,all requests. This can
> help
> >> > them
> >> > > > >> > > understand
> >> > > > >> > > >>>> the
> >> > > > >> > > >>>> >> >> > proposal. I will rewrite this part for more
> >> > > > readability.
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> To be clear, I wasn't suggesting dropping either
> >> > > > section. I
> >> > > > >> > > agree
> >> > > > >> > > >>>> that
> >> > > > >> > > >>>> >> >> they add useful background. I was just
> suggesting
> >> > that
> >> > > we
> >> > > > >> > should
> >> > > > >> > > >>>> discuss
> >> > > > >> > > >>>> >> >> the "acks" setting AFTER discussing the new high
> >> > > > watermark
> >> > > > >> > > >>>> advancement
> >> > > > >> > > >>>> >> >> conditions. We also should discuss acks=0. While
> >> it
> >> > > isn't
> >> > > > >> > > >>>> conceptually
> >> > > > >> > > >>>> >> much
> >> > > > >> > > >>>> >> >> different than acks=1 here, its omission from
> this
> >> > > > section
> >> > > > >> is
> >> > > > >> > > >>>> confusing.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> > Unclean recovery
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> > The plan is to replace the
> >> > > > unclean.leader.election.enable
> >> > > > >> > with
> >> > > > >> > > >>>> >> >> > unclean.recovery.strategy. If the Unclean
> >> Recovery
> >> > is
> >> > > > >> > enabled
> >> > > > >> > > >>>> then it
> >> > > > >> > > >>>> >> >> deals
> >> > > > >> > > >>>> >> >> > with the three options in the
> >> > > > unclean.recovery.strategy.
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> > Let’s refine the Unclean Recovery. We have
> >> already
> >> > > > taken a
> >> > > > >> > > lot of
> >> > > > >> > > >>>> >> >> > suggestions and I hope to enhance the
> >> durability of
> >> > > > Kafka
> >> > > > >> to
> >> > > > >> > > the
> >> > > > >> > > >>>> next
> >> > > > >> > > >>>> >> >> level
> >> > > > >> > > >>>> >> >> > with this KIP.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> I am OK with doing the unclean leader recovery
> >> > > > improvements
> >> > > > >> in
> >> > > > >> > > >>>> this KIP.
> >> > > > >> > > >>>> >> >> However, I think we need to really work on the
> >> > > > configuration
> >> > > > >> > > >>>> settings.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> Configuration overrides are often quite messy.
> For
> >> > > > example,
> >> > > > >> > the
> >> > > > >> > > >>>> cases
> >> > > > >> > > >>>> >> >> where we have log.roll.hours and
> >> log.roll.segment.ms
> >> > ,
> >> > > > the
> >> > > > >> > user
> >> > > > >> > > >>>> has to
> >> > > > >> > > >>>> >> >> remember which one takes precedence, and it is
> not
> >> > > > obvious.
> >> > > > >> > So,
> >> > > > >> > > >>>> rather
> >> > > > >> > > >>>> >> than
> >> > > > >> > > >>>> >> >> creating a new configuration, why not add
> >> additional
> >> > > > values
> >> > > > >> to
> >> > > > >> > > >>>> >> >> "unclean.leader.election.enable"? I think this
> >> will
> >> > be
> >> > > > >> simpler
> >> > > > >> > > for
> >> > > > >> > > >>>> >> people
> >> > > > >> > > >>>> >> >> to understand, and simpler in the code as well.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> What if we continued to use
> >> > > > "unclean.leader.election.enable"
> >> > > > >> > but
> >> > > > >> > > >>>> >> extended
> >> > > > >> > > >>>> >> >> it so that it took a string? Then the string
> could
> >> > have
> >> > > > >> these
> >> > > > >> > > >>>> values:
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> never
> >> > > > >> > > >>>> >> >> never automatically do an unclean leader
> >> election
> >> > > > under
> >> > > > >> > any
> >> > > > >> > > >>>> >> conditions
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> false / default
> >> > > > >> > > >>>> >> >> only do an unclean leader election if there
> >> may
> >> > be
> >> > > > >> > possible
> >> > > > >> > > >>>> data
> >> > > > >> > > >>>> >> loss
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> true / always
> >> > > > >> > > >>>> >> >> always do an unclean leader election if we
> >> can't
> >> > > > >> > immediately
> >> > > > >> > > >>>> elect a
> >> > > > >> > > >>>> >> >> leader
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> It's a bit awkward that false maps to default
> >> rather
> >> > > > than to
> >> > > > >> > > >>>> never. But
> >> > > > >> > > >>>> >> >> this awkwardness exists if we use two different
> >> > > > >> configuration
> >> > > > >> > > keys
> >> > > > >> > > >>>> as
> >> > > > >> > > >>>> >> well.
> >> > > > >> > > >>>> >> >> The reason for the awkwardness is that we simply
> >> > don't
> >> > > > want
> >> > > > >> > most
> >> > > > >> > > >>>> of the
> >> > > > >> > > >>>> >> >> people currently setting
> >> > > > >> unclean.leader.election.enable=false
> >> > > > >> > to
> >> > > > >> > > >>>> get the
> >> > > > >> > > >>>> >> >> "never" behavior. We have to bite that bullet.
> >> Better
> >> > > to
> >> > > > be
> >> > > > >> > > clear
> >> > > > >> > > >>>> and
> >> > > > >> > > >>>> >> >> explicit than hide it.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> Another thing that's a bit awkward is having two
> >> > > > different
> >> > > > >> > ways
> >> > > > >> > > to
> >> > > > >> > > >>>> do
> >> > > > >> > > >>>> >> >> unclean leader election specified in the KIP.
> You
> >> > > > descirbe
> >> > > > >> two
> >> > > > >> > > >>>> methods:
> >> > > > >> > > >>>> >> the
> >> > > > >> > > >>>> >> >> simple "choose the last leader" method, and the
> >> > > "unclean
> >> > > > >> > > recovery
> >> > > > >> > > >>>> >> manager"
> >> > > > >> > > >>>> >> >> method. I understand why you did it this way --
> >> > "choose
> >> > > > the
> >> > > > >> > last
> >> > > > >> > > >>>> >> leader" is
> >> > > > >> > > >>>> >> >> simple, and will help us deliver an
> implementation
> >> > > > quickly,
> >> > > > >> > > while
> >> > > > >> > > >>>> the
> >> > > > >> > > >>>> >> URM
> >> > > > >> > > >>>> >> >> is preferable in the long term. My suggestion
> >> here is
> >> > > to
> >> > > > >> > > separate
> >> > > > >> > > >>>> the
> >> > > > >> > > >>>> >> >> decision of HOW to do unclean leader election
> from
> >> > the
> >> > > > >> > decision
> >> > > > >> > > of
> >> > > > >> > > >>>> WHEN
> >> > > > >> > > >>>> >> to
> >> > > > >> > > >>>> >> >> do it.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> So in other words, have
> >> > > "unclean.leader.election.enable"
> >> > > > >> > specify
> >> > > > >> > > >>>> when we
> >> > > > >> > > >>>> >> >> do unclean leader election, and have a new
> >> > > configuration
> >> > > > >> like
> >> > > > >> > > >>>> >> >> "unclean.recovery.manager.enable" to determine
> if
> >> we
> >> > > use
> >> > > > the
> >> > > > >> > > URM.
> >> > > > >> > > >>>> >> >> Presumably the URM will take some time to get
> >> fully
> >> > > > stable,
> >> > > > >> so
> >> > > > >> > > >>>> this can
> >> > > > >> > > >>>> >> >> default to false for a while, and we can flip
> the
> >> > > > default to
> >> > > > >> > > true
> >> > > > >> > > >>>> when
> >> > > > >> > > >>>> >> we
> >> > > > >> > > >>>> >> >> feel ready.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> The URM is somewhat under-described here. I
> think
> >> we
> >> > > > need a
> >> > > > >> > few
> >> > > > >> > > >>>> >> >> configurations here for it. For example, we
> need a
> >> > > > >> > > configuration to
> >> > > > >> > > >>>> >> specify
> >> > > > >> > > >>>> >> >> how long it should wait for a broker to respond
> to
> >> > its
> >> > > > RPCs
> >> > > > >> > > before
> >> > > > >> > > >>>> >> moving
> >> > > > >> > > >>>> >> >> on. We also need to understand how the URM
> >> interacts
> >> > > with
> >> > > > >> > > >>>> >> >> unclean.leader.election.enable=always. I assume
> >> that
> >> > > with
> >> > > > >> > > "always"
> >> > > > >> > > >>>> we
> >> > > > >> > > >>>> >> will
> >> > > > >> > > >>>> >> >> just unconditionally use the URM rather than
> >> choosing
> >> > > > >> > randomly.
> >> > > > >> > > >>>> But this
> >> > > > >> > > >>>> >> >> should be spelled out in the KIP.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> > DescribeTopicRequest
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> > 1.
> >> > > > >> > > >>>> >> >> > Yes, the plan is to replace the
> >> MetadataRequest
> >> > > with
> >> > > > >> the
> >> > > > >> > > >>>> >> >> > DescribeTopicRequest for the admin clients.
> >> Will
> >> > > > check
> >> > > > >> > the
> >> > > > >> > > >>>> details.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> Sounds good. But as I said, you need to specify
> >> how
> >> > > > >> > AdminClient
> >> > > > >> > > >>>> >> interacts
> >> > > > >> > > >>>> >> >> with the new request. This will involve adding
> >> some
> >> > > > fields
> >> > > > >> to
> >> > > > >> > > >>>> >> >> TopicDescription.java. And you need to specify
> the
> >> > > > changes
> >> > > > >> to
> >> > > > >> > > the
> >> > > > >> > > >>>> >> >> kafka-topics.sh command line tool. Otherwise we
> >> > cannot
> >> > > > use
> >> > > > >> the
> >> > > > >> > > >>>> tool to
> >> > > > >> > > >>>> >> see
> >> > > > >> > > >>>> >> >> the new information.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> The new requests, DescribeTopicRequest and
> >> > > > >> > > >>>> GetReplicaLogInfoRequest,
> >> > > > >> > > >>>> >> need
> >> > > > >> > > >>>> >> >> to have limits placed on them so that their size
> >> > can't
> >> > > be
> >> > > > >> > > >>>> infinite. We
> >> > > > >> > > >>>> >> >> don't want to propagate the current problems of
> >> > > > >> > MetadataRequest,
> >> > > > >> > > >>>> where
> >> > > > >> > > >>>> >> >> clients can request massive responses that can
> >> mess
> >> > up
> >> > > > the
> >> > > > >> JVM
> >> > > > >> > > when
> >> > > > >> > > >>>> >> handled.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> Adding limits is simple for
> >> GetReplicaLogInfoRequest
> >> > --
> >> > > > we
> >> > > > >> can
> >> > > > >> > > >>>> just say
> >> > > > >> > > >>>> >> >> that only 2000 partitions at a time can be
> >> requested.
> >> > > For
> >> > > > >> > > >>>> >> >> DescribeTopicRequest we can probably just limit
> >> to 20
> >> > > > topics
> >> > > > >> > or
> >> > > > >> > > >>>> >> something
> >> > > > >> > > >>>> >> >> like that, to avoid the complexity of doing
> >> > pagination
> >> > > in
> >> > > > >> this
> >> > > > >> > > KIP.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> > 2.
> >> > > > >> > > >>>> >> >> > I can let the broker load the ELR info so
> >> that
> >> > > they
> >> > > > can
> >> > > > >> > > serve
> >> > > > >> > > >>>> the
> >> > > > >> > > >>>> >> >> > DescribeTopicRequest as well.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> Yes, it's fine to add to MetadataCache. In fact,
> >> > you'll
> >> > > > be
> >> > > > >> > > loading
> >> > > > >> > > >>>> it
> >> > > > >> > > >>>> >> >> anyway once it's added to PartitionImage.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> > 3.
> >> > > > >> > > >>>> >> >> > Yeah, it does not make sense to have the
> >> topic
> >> > id
> >> > > if
> >> > > > >> > > >>>> >> >> > DescribeTopicRequest is only used by the
> >> admin
> >> > > > client.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> OK. That makes things simpler. We can always
> >> create a
> >> > > new
> >> > > > >> API
> >> > > > >> > > later
> >> > > > >> > > >>>> >> >> (hopefully not in this KIP!) to query by topic
> ID.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> > Metrics
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> > As for overall cluster health metrics, I think
> >> > > > >> under-min-ISR
> >> > > > >> > > is
> >> > > > >> > > >>>> still
> >> > > > >> > > >>>> >> a
> >> > > > >> > > >>>> >> >> > useful one. ELR is more like a safety belt.
> When
> >> > the
> >> > > > ELR
> >> > > > >> is
> >> > > > >> > > >>>> used, the
> >> > > > >> > > >>>> >> >> > cluster availability has already been
> impacted.
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> > Maybe we can have a metric to count the
> >> partitions
> >> > > that
> >> > > > >> > > sum(ISR,
> >> > > > >> > > >>>> ELR)
> >> > > > >> > > >>>> >> <
> >> > > > >> > > >>>> >> >> min
> >> > > > >> > > >>>> >> >> > ISR. What do you think?
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> How about:
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> A. a metric for the totoal number of
> >> under-min-isr
> >> > > > >> > partitions?
> >> > > > >> > > We
> >> > > > >> > > >>>> don't
> >> > > > >> > > >>>> >> >> have that in Apache Kafka at the moment.
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> B. a metric for the number of unclean leader
> >> > elections
> >> > > we
> >> > > > >> did
> >> > > > >> > > (for
> >> > > > >> > > >>>> >> >> simplicity, it can reset to 0 on controller
> >> restart:
> >> > we
> >> > > > >> expect
> >> > > > >> > > >>>> people to
> >> > > > >> > > >>>> >> >> monitor the change over time anyway)
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> best,
> >> > > > >> > > >>>> >> >> Colin
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> > Yeah, for the ongoing unclean recoveries, the
> >> > > > controller
> >> > > > >> can
> >> > > > >> > > >>>> keep an
> >> > > > >> > > >>>> >> >> > accurate count through failover because
> >> partition
> >> > > > >> > registration
> >> > > > >> > > >>>> can
> >> > > > >> > > >>>> >> >> indicate
> >> > > > >> > > >>>> >> >> > whether a recovery is needed. However, for the
> >> > > happened
> >> > > > >> > ones,
> >> > > > >> > > >>>> unless
> >> > > > >> > > >>>> >> we
> >> > > > >> > > >>>> >> >> > want to persist the number somewhere, we can
> >> only
> >> > > > figure
> >> > > > >> it
> >> > > > >> > > out
> >> > > > >> > > >>>> from
> >> > > > >> > > >>>> >> the
> >> > > > >> > > >>>> >> >> > log.
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> > On Tue, Sep 12, 2023 at 3:16 PM Colin McCabe <
> >> > > > >> > > cmcc...@apache.org
> >> > > > >> > > >>>> >
> >> > > > >> > > >>>> >> wrote:
> >> > > > >> > > >>>> >> >> >
> >> > > > >> > > >>>> >> >> >> Also, we should have metrics that show what
> is
> >> > going
> >> > > > on
> >> > > > >> > with
> >> > > > >> > > >>>> regard
> >> > > > >> > > >>>> >> to
> >> > > > >> > > >>>> >> >> the
> >> > > > >> > > >>>> >> >> >> eligible replica set. I'm not sure exactly
> >> what to
> >> > > > >> suggest,
> >> > > > >> > > but
> >> > > > >> > > >>>> >> >> something
> >> > > > >> > > >>>> >> >> >> that could identify when things are going
> >> wrong in
> >> > > the
> >> > > > >> > > clsuter.
> >> > > > >> > > >>>> >> >> >>
> >> > > > >> > > >>>> >> >> >> For example, maybe a metric for partitions
> >> > > containing
> >> > > > >> > > replicas
> >> > > > >> > > >>>> that
> >> > > > >> > > >>>> >> are
> >> > > > >> > > >>>> >> >> >> ineligible to be leader? That would show a
> >> spike
> >> > > when
> >> > > > a
> >> > > > >> > > broker
> >> > > > >> > > >>>> had an
> >> > > > >> > > >>>> >> >> >> unclean restart.
> >> > > > >> > > >>>> >> >> >>
> >> > > > >> > > >>>> >> >> >> Ideally, we'd also have a metric that
> indicates
> >> > when
> >> > > > an
> >> > > > >> > > unclear
> >> > > > >> > > >>>> >> leader
> >> > > > >> > > >>>> >> >> >> election or a recovery happened. It's a bit
> >> tricky
> >> > > > >> because
> >> > > > >> > > the
> >> > > > >> > > >>>> simple
> >> > > > >> > > >>>> >> >> >> thing, of tracking it per controller, may be
> a
> >> bit
> >> > > > >> > confusing
> >> > > > >> > > >>>> during
> >> > > > >> > > >>>> >> >> >> failovers.
> >> > > > >> > > >>>> >> >> >>
> >> > > > >> > > >>>> >> >> >> best,
> >> > > > >> > > >>>> >> >> >> Colin
> >> > > > >> > > >>>> >> >> >>
> >> > > > >> > > >>>> >> >> >>
> >> > > > >> > > >>>> >> >> >> On Tue, Sep 12, 2023, at 14:25, Colin McCabe
> >> > wrote:
> >> > > > >> > > >>>> >> >> >> > Hi Calvin,
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > Thanks for the KIP. I think this is a great
> >> > > > >> improvement.
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> >> Additional High Watermark advance
> >> requirement
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > Typo: change "advance" to "advancement"
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> >> A bit recap of some key concepts.
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > Typo: change "bit" to "quick"
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> >> Ack=1/all produce request. It defines when
> >> the
> >> > > > Kafka
> >> > > > >> > > server
> >> > > > >> > > >>>> should
> >> > > > >> > > >>>> >> >> >> respond to the produce request
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > I think this section would be clearer if we
> >> > talked
> >> > > > >> about
> >> > > > >> > > the
> >> > > > >> > > >>>> new
> >> > > > >> > > >>>> >> high
> >> > > > >> > > >>>> >> >> >> > watermark advancement requirement first,
> and
> >> > THEN
> >> > > > >> talked
> >> > > > >> > > >>>> about its
> >> > > > >> > > >>>> >> >> >> > impact on acks=0, acks=1, and acks=all.
> >> > > > acks=all
> >> > > > >> is
> >> > > > >> > of
> >> > > > >> > > >>>> course
> >> > > > >> > > >>>> >> the
> >> > > > >> > > >>>> >> >> >> > main case we care about here, so it would
> be
> >> > good
> >> > > to
> >> > > > >> lead
> >> > > > >> > > with
> >> > > > >> > > >>>> >> that,
> >> > > > >> > > >>>> >> >> >> > rather than delving into the technicalities
> >> of
> >> > > > acks=0/1
> >> > > > >> > > first.
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> >> Unclean recovery
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > So, here you are introducing a new
> >> > configuration,
> >> > > > >> > > >>>> >> >> >> > unclean.recovery.strategy. The difficult
> >> thing
> >> > > here
> >> > > > is
> >> > > > >> > that
> >> > > > >> > > >>>> there
> >> > > > >> > > >>>> >> is a
> >> > > > >> > > >>>> >> >> >> > lot of overlap with
> >> > > unclean.leader.election.enable.
> >> > > > So
> >> > > > >> we
> >> > > > >> > > >>>> have 3
> >> > > > >> > > >>>> >> >> >> > different settings for
> >> > unclean.recovery.strategy,
> >> > > > plus
> >> > > > >> 2
> >> > > > >> > > >>>> different
> >> > > > >> > > >>>> >> >> >> > settings for
> unclean.leader.election.enable,
> >> > > giving
> >> > > > a
> >> > > > >> > cross
> >> > > > >> > > >>>> >> product of
> >> > > > >> > > >>>> >> >> >> > 6 different options. The following "unclean
> >> > > recovery
> >> > > > >> > > manager"
> >> > > > >> > > >>>> >> section
> >> > > > >> > > >>>> >> >> >> > only applies to one fo those 6 different
> >> > > > possibilities
> >> > > > >> (I
> >> > > > >> > > >>>> think?)
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > I simply don't think we need so many
> >> different
> >> > > > election
> >> > > > >> > > types.
> >> > > > >> > > >>>> >> Really
> >> > > > >> > > >>>> >> >> >> > the use-cases we need are people who want
> NO
> >> > > unclean
> >> > > > >> > > >>>> elections,
> >> > > > >> > > >>>> >> people
> >> > > > >> > > >>>> >> >> >> > who want "the reasonable thing" and people
> >> who
> >> > > want
> >> > > > >> > > >>>> avaialbility at
> >> > > > >> > > >>>> >> >> all
> >> > > > >> > > >>>> >> >> >> > costs.
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > Overall, I feel like the first half of the
> >> KIP
> >> > is
> >> > > > about
> >> > > > >> > the
> >> > > > >> > > >>>> ELR,
> >> > > > >> > > >>>> >> and
> >> > > > >> > > >>>> >> >> >> > the second half is about reworking unclean
> >> > leader
> >> > > > >> > > election. It
> >> > > > >> > > >>>> >> might
> >> > > > >> > > >>>> >> >> be
> >> > > > >> > > >>>> >> >> >> > better to move that second half to a
> separate
> >> > KIP
> >> > > so
> >> > > > >> that
> >> > > > >> > > we
> >> > > > >> > > >>>> can
> >> > > > >> > > >>>> >> >> figure
> >> > > > >> > > >>>> >> >> >> > it out fully. It should be fine to punt
> this
> >> > until
> >> > > > >> later
> >> > > > >> > > and
> >> > > > >> > > >>>> just
> >> > > > >> > > >>>> >> have
> >> > > > >> > > >>>> >> >> >> > the current behavior on empty ELR be
> waiting
> >> for
> >> > > the
> >> > > > >> last
> >> > > > >> > > >>>> known
> >> > > > >> > > >>>> >> leader
> >> > > > >> > > >>>> >> >> >> > to return. After all, that's what we do
> >> today.
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> >> DescribeTopicRequest
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > Is the intention for AdminClient to use
> this
> >> RPC
> >> > > for
> >> > > > >> > > >>>> >> >> >> > Admin#describeTopics ? If so, we need to
> >> > describe
> >> > > > all
> >> > > > >> of
> >> > > > >> > > the
> >> > > > >> > > >>>> >> changes
> >> > > > >> > > >>>> >> >> to
> >> > > > >> > > >>>> >> >> >> > the admin client API, as well as changes to
> >> > > > >> command-line
> >> > > > >> > > >>>> tools like
> >> > > > >> > > >>>> >> >> >> > kafka-topics.sh (if there are any). For
> >> example,
> >> > > you
> >> > > > >> will
> >> > > > >> > > >>>> probably
> >> > > > >> > > >>>> >> >> need
> >> > > > >> > > >>>> >> >> >> > changes to TopicDescription.java. You will
> >> also
> >> > > > need to
> >> > > > >> > > >>>> provide
> >> > > > >> > > >>>> >> all of
> >> > > > >> > > >>>> >> >> >> > the things that admin client needs -- for
> >> > example,
> >> > > > >> > > >>>> >> >> >> > TopicAuthorizedOperations.
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > I also don't think the controller should
> >> serve
> >> > > this
> >> > > > >> > > request.
> >> > > > >> > > >>>> We
> >> > > > >> > > >>>> >> want
> >> > > > >> > > >>>> >> >> to
> >> > > > >> > > >>>> >> >> >> > minimize load on the controller. Just like
> >> with
> >> > > the
> >> > > > >> other
> >> > > > >> > > >>>> metadata
> >> > > > >> > > >>>> >> >> >> > requests like MetadataRequest, this should
> be
> >> > > > served by
> >> > > > >> > > >>>> brokers.
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > It's a bit confusing why both topic ID and
> >> topic
> >> > > > name
> >> > > > >> are
> >> > > > >> > > >>>> provided
> >> > > > >> > > >>>> >> to
> >> > > > >> > > >>>> >> >> >> > this API. Is the intention that callers
> >> should
> >> > set
> >> > > > one
> >> > > > >> > but
> >> > > > >> > > >>>> not the
> >> > > > >> > > >>>> >> >> >> > other? Or both? This needs to be clarified.
> >> > Also,
> >> > > > if we
> >> > > > >> > do
> >> > > > >> > > >>>> want to
> >> > > > >> > > >>>> >> >> >> > support lookups by UUID, that is another
> >> thing
> >> > > that
> >> > > > >> needs
> >> > > > >> > > to
> >> > > > >> > > >>>> be
> >> > > > >> > > >>>> >> added
> >> > > > >> > > >>>> >> >> >> > to adminclient.
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > In general, I feel like this should also
> >> > probably
> >> > > be
> >> > > > >> its
> >> > > > >> > > own
> >> > > > >> > > >>>> KIP
> >> > > > >> > > >>>> >> since
> >> > > > >> > > >>>> >> >> >> > it's fairly complex
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > best,
> >> > > > >> > > >>>> >> >> >> > Colin
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> >
> >> > > > >> > > >>>> >> >> >> > On Thu, Aug 10, 2023, at 15:46, Calvin Liu
> >> > wrote:
> >> > > > >> > > >>>> >> >> >> >> Hi everyone,
> >> > > > >> > > >>>> >> >> >> >> I'd like to discuss a series of
> enhancement
> >> to
> >> > > the
> >> > > > >> > > >>>> replication
> >> > > > >> > > >>>> >> >> protocol.
> >> > > > >> > > >>>> >> >> >> >>
> >> > > > >> > > >>>> >> >> >> >> A partition replica can experience local
> >> data
> >> > > loss
> >> > > > in
> >> > > > >> > > unclean
> >> > > > >> > > >>>> >> >> shutdown
> >> > > > >> > > >>>> >> >> >> >> scenarios where unflushed data in the OS
> >> page
> >> > > > cache is
> >> > > > >> > > lost
> >> > > > >> > > >>>> - such
> >> > > > >> > > >>>> >> >> as an
> >> > > > >> > > >>>> >> >> >> >> availability zone power outage or a server
> >> > error.
> >> > > > The
> >> > > > >> > > Kafka
> >> > > > >> > > >>>> >> >> replication
> >> > > > >> > > >>>> >> >> >> >> protocol is designed to handle these
> >> situations
> >> > > by
> >> > > > >> > > removing
> >> > > > >> > > >>>> such
> >> > > > >> > > >>>> >> >> >> replicas
> >> > > > >> > > >>>> >> >> >> >> from the ISR and only re-adding them once
> >> they
> >> > > have
> >> > > > >> > caught
> >> > > > >> > > >>>> up and
> >> > > > >> > > >>>> >> >> >> therefore
> >> > > > >> > > >>>> >> >> >> >> recovered any lost data. This prevents
> >> replicas
> >> > > > that
> >> > > > >> > lost
> >> > > > >> > > an
> >> > > > >> > > >>>> >> >> arbitrary
> >> > > > >> > > >>>> >> >> >> log
> >> > > > >> > > >>>> >> >> >> >> suffix, which included committed data,
> from
> >> > being
> >> > > > >> > elected
> >> > > > >> > > >>>> leader.
> >> > > > >> > > >>>> >> >> >> >> However, there is a "last replica
> standing"
> >> > state
> >> > > > >> which
> >> > > > >> > > when
> >> > > > >> > > >>>> >> combined
> >> > > > >> > > >>>> >> >> >> with
> >> > > > >> > > >>>> >> >> >> >> a data loss unclean shutdown event can
> turn
> >> a
> >> > > local
> >> > > > >> data
> >> > > > >> > > loss
> >> > > > >> > > >>>> >> >> scenario
> >> > > > >> > > >>>> >> >> >> into
> >> > > > >> > > >>>> >> >> >> >> a global data loss scenario, i.e.,
> committed
> >> > data
> >> > > > can
> >> > > > >> be
> >> > > > >> > > >>>> removed
> >> > > > >> > > >>>> >> from
> >> > > > >> > > >>>> >> >> >> all
> >> > > > >> > > >>>> >> >> >> >> replicas. When the last replica in the ISR
> >> > > > experiences
> >> > > > >> > an
> >> > > > >> > > >>>> unclean
> >> > > > >> > > >>>> >> >> >> shutdown
> >> > > > >> > > >>>> >> >> >> >> and loses committed data, it will be
> >> reelected
> >> > > > leader
> >> > > > >> > > after
> >> > > > >> > > >>>> >> starting
> >> > > > >> > > >>>> >> >> up
> >> > > > >> > > >>>> >> >> >> >> again, causing rejoining followers to
> >> truncate
> >> > > > their
> >> > > > >> > logs
> >> > > > >> > > and
> >> > > > >> > > >>>> >> thereby
> >> > > > >> > > >>>> >> >> >> >> removing the last copies of the committed
> >> > records
> >> > > > >> which
> >> > > > >> > > the
> >> > > > >> > > >>>> leader
> >> > > > >> > > >>>> >> >> lost
> >> > > > >> > > >>>> >> >> >> >> initially.
> >> > > > >> > > >>>> >> >> >> >>
> >> > > > >> > > >>>> >> >> >> >> The new KIP will maximize the protection
> and
> >> > > > provides
> >> > > > >> > > >>>> MinISR-1
> >> > > > >> > > >>>> >> >> >> tolerance to
> >> > > > >> > > >>>> >> >> >> >> data loss unclean shutdown events.
> >> > > > >> > > >>>> >> >> >> >>
> >> > > > >> > > >>>> >> >> >> >>
> >> > > > >> > > >>>> >> >> >>
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >>
> >> > > > >> > > >>>>
> >> > > > >> > >
> >> > > > >> >
> >> > > > >>
> >> > > >
> >> > >
> >> >
> >>
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-966%3A+Eligible+Leader+Replicas
> >> > > > >> > > >>>> >> >> >>
> >> > > > >> > > >>>> >> >>
> >> > > > >> > > >>>> >>
> >> > > > >> > > >>>>
> >> > > > >> > > >>>
> >> > > > >> > >
> >> > > > >> >
> >> > > > >>
> >> > > >
> >> > >
> >> >
> >>
> >
>
