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From Kowshik Prakasam <kpraka...@confluent.io>
Subject Re: [DISCUSS] KIP-584: Versioning scheme for features
Date Fri, 03 Apr 2020 20:04:25 GMT
Hey Boyang,

Thanks for the feedback! I've updated the KIP. Please find below my
response.

> 1. Do you mind updating the non-goal section as we are introducing a
> --feature-force-downgrade to address downgrade concern?

(Kowshik): This was already mentioned. Look for non-goal: 1-b.

> 2. For the flags `--feature` seems to be a redundant prefix, as the script
> is already called `kafka-features.sh`. They could just be called
> `--upgrade` and `--force-downgrade`.

(Kowshik): Great point! Done.

> 3. I don't feel strong to require a confirmation for a normal feature
> upgrade, unless there are other existing scripts doing so.

(Kowshik): Done. Removed now. We now ask for a confirmation only for
downgrades.

> 4. How could we know the existing feature versions when user are only
> executing upgrades? Does the `kafka-features.sh` always send a
> DescribeFeatureRequest to broker first?

(Kowshik): For deletes, yes it will make an ApiVersionsRequest call to show
the
versions of the features. Perhaps the ApiVersionsRequest can be sent
to just the controller to avoid questions on consistency, but that's
an implementation detail.

> 5. I'm not 100% sure, but a script usually use the same flag once, so
maybe
> we should also do that for `--upgrade-feature`? Instead of flagging twice
> for different features, a comma separated list of (feature:max_version)
> will be expected, or something like that.

(Kowshik): Done. I'm using a comma-separated list now.

> 6. "The node data shall be readable via existing ZK tooling" Just trying
to
> clarify, we are not introducing ZK direct read tool in this KIP correct?
As
> for KIP-500 <https://issues.apache.org/jira/browse/KIP-500> we are
eventually going to deprecate all direct ZK access tools.

(Kowshik): Done. Yes, we are not intending to add such a tool. I was just
saying that
if we ever want to read it from ZK, then it's readable via ZK cli (in the
interim).
I have modified the text conveying the intent to support reads via
ApiVersionsRequest only (optionally this request can be directed at the
controller to
void questions on consistency, but that's an implementation detail).

> 7. Could we have a centralized section called `Public Interfaces` to
> summarize all the public API changes? This is a required section in a KIP.
> And we should also write down the new error codes we will be introducing
in
> this KIP, and include both new and old error codes in the Response schema
> comment if possible. For example, UpdateFeatureResponse could expect a
> `NOT_CONTROLLER` error code.

(Kowshik): Done. The error codes have been documented in the response
schemas now.
Added a new section titled "New or Changed Public Interfaces" summarizing
only the
changes made to the public interfaces.


Cheers,
Kowshik


On Fri, Apr 3, 2020 at 9:39 AM Boyang Chen <reluctanthero104@gmail.com>
wrote:

> Hey Kowshik,
>
> thanks for getting the KIP updated. The Zookeeper routing approach makes
> sense and simplifies the changes.
> Some follow-ups:
>
> 1. Do you mind updating the non-goal section as we are introducing a
> --feature-force-downgrade to address downgrade concern?
>
> 2. For the flags `--feature` seems to be a redundant prefix, as the script
> is already called `kafka-features.sh`. They could just be called
> `--upgrade` and `--force-downgrade`.
>
> 3. I don't feel strong to require a confirmation for a normal feature
> upgrade, unless there are other existing scripts doing so.
>
> 4. How could we know the existing feature versions when user are only
> executing upgrades? Does the `kafka-features.sh` always send a
> DescribeFeatureRequest to broker first?
>
> 5. I'm not 100% sure, but a script usually use the same flag once, so maybe
> we should also do that for `--upgrade-feature`? Instead of flagging twice
> for different features, a comma separated list of (feature:max_version)
> will be expected, or something like that.
>
> 6. "The node data shall be readable via existing ZK tooling" Just trying to
> clarify, we are not introducing ZK direct read tool in this KIP correct? As
> for KIP-500 <https://issues.apache.org/jira/browse/KIP-500> we are
> eventually going to deprecate all direct ZK access tools.
>
> 7. Could we have a centralized section called `Public Interfaces` to
> summarize all the public API changes? This is a required section in a KIP.
> And we should also write down the new error codes we will be introducing in
> this KIP, and include both new and old error codes in the Response schema
> comment if possible. For example, UpdateFeatureResponse could expect a
> `NOT_CONTROLLER` error code.
>
>
> Boyang
>
> On Fri, Apr 3, 2020 at 3:15 AM Kowshik Prakasam <kprakasam@confluent.io>
> wrote:
>
> > Hi all,
> >
> > Any other feedback on this KIP before we start the vote?
> >
> >
> > Cheers,
> > Kowshik
> >
> > On Fri, Apr 3, 2020 at 1:27 AM Kowshik Prakasam <kprakasam@confluent.io>
> > wrote:
> >
> > > Hey Jun,
> > >
> > > Thanks a lot for the great feedback! Please note that the design
> > > has changed a little bit on the KIP, and we now propagate the finalized
> > > features metadata only via ZK watches (instead of UpdateMetadataRequest
> > > from the controller).
> > >
> > > Please find below my response to your questions/feedback, with the
> prefix
> > > "(Kowshik):".
> > >
> > > > 100. UpdateFeaturesRequest/UpdateFeaturesResponse
> > > > 100.1 Since this request waits for responses from brokers, should we
> > add
> > > a
> > > > timeout in the request (like createTopicRequest)?
> > >
> > > (Kowshik): Great point! Done. I have added a timeout field. Note: we no
> > > longer
> > > wait for responses from brokers, since the design has been changed so
> > that
> > > the
> > > features information is propagated via ZK. Nevertheless, it is right to
> > > have a timeout
> > > for the request.
> > >
> > > > 100.2 The response schema is a bit weird. Typically, the response
> just
> > > > shows an error code and an error message, instead of echoing the
> > request.
> > >
> > > (Kowshik): Great point! Yeah, I have modified it to just return an
> error
> > > code and a message.
> > > Previously it was not echoing the "request", rather it was returning
> the
> > > latest set of
> > > cluster-wide finalized features (after applying the updates). But you
> are
> > > right,
> > > the additional info is not required, so I have removed it from the
> > > response schema.
> > >
> > > > 100.3 Should we add a separate request to list/describe the existing
> > > > features?
> > >
> > > (Kowshik): This is already present in the KIP via the
> 'DescribeFeatures'
> > > Admin API,
> > > which, underneath covers uses the ApiVersionsRequest to list/describe
> the
> > > existing features. Please read the 'Tooling support' section.
> > >
> > > > 100.4 We are mixing ADD_OR_UPDATE and DELETE in a single request. For
> > > > DELETE, the version field doesn't make sense. So, I guess the broker
> > just
> > > > ignores this? An alternative way is to have a separate
> > > DeleteFeaturesRequest
> > >
> > > (Kowshik): Great point! I have modified the KIP now to have 2 separate
> > > controller APIs
> > > serving these different purposes:
> > > 1. updateFeatures
> > > 2. deleteFeatures
> > >
> > > > 100.5 In UpdateFeaturesResponse, we have "The monotonically
> increasing
> > > > version of the metadata for finalized features." I am wondering why
> the
> > > > ordering is important?
> > >
> > > (Kowshik): In the latest KIP write-up, it is called epoch (instead of
> > > version), and
> > > it is just the ZK node version. Basically, this is the epoch for the
> > > cluster-wide
> > > finalized feature version metadata. This metadata is served to clients
> > via
> > > the
> > > ApiVersionsResponse (for reads). We propagate updates from the
> > '/features'
> > > ZK node
> > > to all brokers, via ZK watches setup by each broker on the '/features'
> > > node.
> > >
> > > Now here is why the ordering is important:
> > > ZK watches don't propagate at the same time. As a result, the
> > > ApiVersionsResponse
> > > is eventually consistent across brokers. This can introduce cases
> > > where clients see an older lower epoch of the features metadata, after
> a
> > > more recent
> > > higher epoch was returned at a previous point in time. We expect
> clients
> > > to always employ the rule that the latest received higher epoch of
> > metadata
> > > always trumps an older smaller epoch. Those clients that are external
> to
> > > Kafka should strongly consider discovering the latest metadata once
> > during
> > > startup from the brokers, and if required refresh the metadata
> > periodically
> > > (to get the latest metadata).
> > >
> > > > 100.6 Could you specify the required ACL for this new request?
> > >
> > > (Kowshik): What is ACL, and how could I find out which one to specify?
> > > Please could you provide me some pointers? I'll be glad to update the
> > > KIP once I know the next steps.
> > >
> > > > 101. For the broker registration ZK node, should we bump up the
> version
> > > in
> > > the json?
> > >
> > > (Kowshik): Great point! Done. I've increased the version in the broker
> > > json by 1.
> > >
> > > > 102. For the /features ZK node, not sure if we need the epoch field.
> > Each
> > > > ZK node has an internal version field that is incremented on every
> > > update.
> > >
> > > (Kowshik): Great point! Done. I'm using the ZK node version now,
> instead
> > > of explicitly
> > > incremented epoch.
> > >
> > > > 103. "Enabling the actual semantics of a feature version cluster-wide
> > is
> > > > left to the discretion of the logic implementing the feature (ex: can
> > be
> > > > done via dynamic broker config)." Does that mean the broker
> > registration
> > > ZK
> > > > node will be updated dynamically when this happens?
> > >
> > > (Kowshik): Not really. The text was just conveying that a broker could
> > > "know" of
> > > a new feature version, but it does not mean the broker should have also
> > > activated the effects of the feature version. Knowing vs activation
> are 2
> > > separate things,
> > > and the latter can be achieved by dynamic config. I have reworded the
> > text
> > > to
> > > make this clear to the reader.
> > >
> > >
> > > > 104. UpdateMetadataRequest
> > > > 104.1 It would be useful to describe when the feature metadata is
> > > included
> > > > in the request. My understanding is that it's only included if (1)
> > there
> > > is
> > > > a change to the finalized feature; (2) broker restart; (3) controller
> > > > failover.
> > > > 104.2 The new fields have the following versions. Why are the
> versions
> > 3+
> > > > when the top version is bumped to 6?
> > > >       "fields":  [
> > > >         {"name": "Name", "type":  "string", "versions":  "3+",
> > > >           "about": "The name of the feature."},
> > > >         {"name":  "Version", "type":  "int64", "versions":  "3+",
> > > >           "about": "The finalized version for the feature."}
> > > >       ]
> > >
> > > (Kowshik): With the new improved design, we have completely eliminated
> > the
> > > need to
> > > use UpdateMetadataRequest. This is because we now rely on ZK to deliver
> > the
> > > notifications for changes to the '/features' ZK node.
> > >
> > > > 105. kafka-features.sh: Instead of using update/delete, perhaps it's
> > > better
> > > > to use enable/disable?
> > >
> > > (Kowshik): For delete, yes, I have changed it so that we instead call
> it
> > > 'disable'.
> > > However for 'update', it can now also refer to either an upgrade or a
> > > forced downgrade.
> > > Therefore, I have left it the way it is, just calling it as just
> > 'update'.
> > >
> > >
> > > Cheers,
> > > Kowshik
> > >
> > > On Tue, Mar 31, 2020 at 6:51 PM Jun Rao <jun@confluent.io> wrote:
> > >
> > >> Hi, Kowshik,
> > >>
> > >> Thanks for the KIP. Looks good overall. A few comments below.
> > >>
> > >> 100. UpdateFeaturesRequest/UpdateFeaturesResponse
> > >> 100.1 Since this request waits for responses from brokers, should we
> > add a
> > >> timeout in the request (like createTopicRequest)?
> > >> 100.2 The response schema is a bit weird. Typically, the response just
> > >> shows an error code and an error message, instead of echoing the
> > request.
> > >> 100.3 Should we add a separate request to list/describe the existing
> > >> features?
> > >> 100.4 We are mixing ADD_OR_UPDATE and DELETE in a single request. For
> > >> DELETE, the version field doesn't make sense. So, I guess the broker
> > just
> > >> ignores this? An alternative way is to have a separate
> > >> DeleteFeaturesRequest
> > >> 100.5 In UpdateFeaturesResponse, we have "The monotonically increasing
> > >> version of the metadata for finalized features." I am wondering why
> the
> > >> ordering is important?
> > >> 100.6 Could you specify the required ACL for this new request?
> > >>
> > >> 101. For the broker registration ZK node, should we bump up the
> version
> > in
> > >> the json?
> > >>
> > >> 102. For the /features ZK node, not sure if we need the epoch field.
> > Each
> > >> ZK node has an internal version field that is incremented on every
> > update.
> > >>
> > >> 103. "Enabling the actual semantics of a feature version cluster-wide
> is
> > >> left to the discretion of the logic implementing the feature (ex: can
> be
> > >> done via dynamic broker config)." Does that mean the broker
> registration
> > >> ZK
> > >> node will be updated dynamically when this happens?
> > >>
> > >> 104. UpdateMetadataRequest
> > >> 104.1 It would be useful to describe when the feature metadata is
> > included
> > >> in the request. My understanding is that it's only included if (1)
> there
> > >> is
> > >> a change to the finalized feature; (2) broker restart; (3) controller
> > >> failover.
> > >> 104.2 The new fields have the following versions. Why are the versions
> > 3+
> > >> when the top version is bumped to 6?
> > >>       "fields":  [
> > >>         {"name": "Name", "type":  "string", "versions":  "3+",
> > >>           "about": "The name of the feature."},
> > >>         {"name":  "Version", "type":  "int64", "versions":  "3+",
> > >>           "about": "The finalized version for the feature."}
> > >>       ]
> > >>
> > >> 105. kafka-features.sh: Instead of using update/delete, perhaps it's
> > >> better
> > >> to use enable/disable?
> > >>
> > >> Jun
> > >>
> > >> On Tue, Mar 31, 2020 at 5:29 PM Kowshik Prakasam <
> > kprakasam@confluent.io>
> > >> wrote:
> > >>
> > >> > Hey Boyang,
> > >> >
> > >> > Thanks for the great feedback! I have updated the KIP based on your
> > >> > feedback.
> > >> > Please find my response below for your comments, look for sentences
> > >> > starting
> > >> > with "(Kowshik)" below.
> > >> >
> > >> >
> > >> > > 1. "When is it safe for the brokers to begin handling EOS traffic"
> > >> could
> > >> > be
> > >> > > converted as "When is it safe for the brokers to start serving
new
> > >> > > Exactly-Once(EOS) semantics" since EOS is not explained earlier
in
> > the
> > >> > > context.
> > >> >
> > >> > (Kowshik): Great point! Done.
> > >> >
> > >> > > 2. In the *Explanation *section, the metadata version number
part
> > >> seems a
> > >> > > bit blurred. Could you point a reference to later section that
we
> > >> going
> > >> > to
> > >> > > store it in Zookeeper and update it every time when there is
a
> > feature
> > >> > > change?
> > >> >
> > >> > (Kowshik): Great point! Done. I've added a reference in the KIP.
> > >> >
> > >> >
> > >> > > 3. For the feature downgrade, although it's a Non-goal of the
KIP,
> > for
> > >> > > features such as group coordinator semantics, there is no legal
> > >> scenario
> > >> > to
> > >> > > perform a downgrade at all. So having downgrade door open is
> pretty
> > >> > > error-prone as human faults happen all the time. I'm assuming
as
> new
> > >> > > features are implemented, it's not very hard to add a flag during
> > >> feature
> > >> > > creation to indicate whether this feature is "downgradable".
Could
> > you
> > >> > > explain a bit more on the extra engineering effort for shipping
> this
> > >> KIP
> > >> > > with downgrade protection in place?
> > >> >
> > >> > (Kowshik): Great point! I'd agree and disagree here. While I agree
> > that
> > >> > accidental
> > >> > downgrades can cause problems, I also think sometimes downgrades
> > should
> > >> > be allowed for emergency reasons (not all downgrades cause issues).
> > >> > It is just subjective to the feature being downgraded.
> > >> >
> > >> > To be more strict about feature version downgrades, I have modified
> > the
> > >> KIP
> > >> > proposing that we mandate a `--force-downgrade` flag be used in the
> > >> > UPDATE_FEATURES api
> > >> > and the tooling, whenever the human is downgrading a finalized
> feature
> > >> > version.
> > >> > Hopefully this should cover the requirement, until we find the need
> > for
> > >> > advanced downgrade support.
> > >> >
> > >> > > 4. "Each broker’s supported dictionary of feature versions
will be
> > >> > defined
> > >> > > in the broker code." So this means in order to restrict a certain
> > >> > feature,
> > >> > > we need to start the broker first and then send a feature gating
> > >> request
> > >> > > immediately, which introduces a time gap and the intended-to-close
> > >> > feature
> > >> > > could actually serve request during this phase. Do you think
we
> > should
> > >> > also
> > >> > > support configurations as well so that admin user could freely
> roll
> > >> up a
> > >> > > cluster with all nodes complying the same feature gating, without
> > >> > worrying
> > >> > > about the turnaround time to propagate the message only after
the
> > >> cluster
> > >> > > starts up?
> > >> >
> > >> > (Kowshik): This is a great point/question. One of the expectations
> out
> > >> of
> > >> > this KIP, which is
> > >> > already followed in the broker, is the following.
> > >> >  - Imagine at time T1 the broker starts up and registers it’s
> presence
> > >> in
> > >> > ZK,
> > >> >    along with advertising it’s supported features.
> > >> >  - Imagine at a future time T2 the broker receives the
> > >> > UpdateMetadataRequest
> > >> >    from the controller, which contains the latest finalized features
> > as
> > >> > seen by
> > >> >    the controller. The broker validates this data against it’s
> > supported
> > >> > features to
> > >> >    make sure there is no mismatch (it will shutdown if there is an
> > >> > incompatibility).
> > >> >
> > >> > It is expected that during the time between the 2 events T1 and T2,
> > the
> > >> > broker is
> > >> > almost a silent entity in the cluster. It does not add any value to
> > the
> > >> > cluster, or carry
> > >> > out any important broker activities. By “important”, I mean it
is
> not
> > >> doing
> > >> > mutations
> > >> > on it’s persistence, not mutating critical in-memory state, won’t
be
> > >> > serving
> > >> > produce/fetch requests. Note it doesn’t even know it’s assigned
> > >> partitions
> > >> > until
> > >> > it receives UpdateMetadataRequest from controller. Anything the
> broker
> > >> is
> > >> > doing up
> > >> > until this point is not damaging/useful.
> > >> >
> > >> > I’ve clarified the above in the KIP, see this new section:
> > >> >
> > >> >
> > >>
> >
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-584%3A+Versioning+scheme+for+features#KIP-584:Versioningschemeforfeatures-Incompatiblebrokerlifetime
> > >> > .
> > >> >
> > >> > > 5. "adding a new Feature, updating or deleting an existing
> Feature",
> > >> may
> > >> > be
> > >> > > I misunderstood something, I thought the features are defined
in
> > >> broker
> > >> > > code, so admin could not really create a new feature?
> > >> >
> > >> > (Kowshik): Great point! You understood this right. Here adding a
> > feature
> > >> > means we are
> > >> > adding a cluster-wide finalized *max* version for a feature that was
> > >> > previously never finalized.
> > >> > I have clarified this in the KIP now.
> > >> >
> > >> > > 6. I think we need a separate error code like
> > >> FEATURE_UPDATE_IN_PROGRESS
> > >> > to
> > >> > > reject a concurrent feature update request.
> > >> >
> > >> > (Kowshik): Great point! I have modified the KIP adding the above
> (see
> > >> > 'Tooling support -> Admin API changes').
> > >> >
> > >> > > 7. I think we haven't discussed the alternative solution to pass
> the
> > >> > > feature information through Zookeeper. Is that mentioned in the
> KIP
> > to
> > >> > > justify why using UpdateMetadata is more favorable?
> > >> >
> > >> > (Kowshik): Nice question! The broker reads finalized feature info
> > >> stored in
> > >> > ZK,
> > >> > only during startup when it does a validation. When serving
> > >> > `ApiVersionsRequest`, the
> > >> > broker does not read this info from ZK directly. I'd imagine the
> risk
> > is
> > >> > that it can increase
> > >> > the ZK read QPS which can be a bottleneck for the system. Today, in
> > >> Kafka
> > >> > we use the
> > >> > controller to fan out ZK updates to brokers and we want to stick to
> > that
> > >> > pattern to avoid
> > >> > the ZK read bottleneck when serving `ApiVersionsRequest`.
> > >> >
> > >> > > 8. I was under the impression that user could configure a range
of
> > >> > > supported versions, what's the trade-off for allowing single
> > finalized
> > >> > > version only?
> > >> >
> > >> > (Kowshik): Great question! The finalized version of a feature
> > basically
> > >> > refers to
> > >> > the cluster-wide finalized feature "maximum" version. For example,
> if
> > >> the
> > >> > 'group_coordinator' feature
> > >> > has the finalized version set to 10, then, it means that
> cluster-wide
> > >> all
> > >> > versions upto v10 are
> > >> > supported for this feature. However, note that if some version (ex:
> > v0)
> > >> > gets deprecated
> > >> > for this feature, then we don’t convey that using this scheme (also
> > >> > supporting deprecation is a non-goal).
> > >> >
> > >> > (Kowshik): I’ve now modified the KIP at all points, refering to
> > >> finalized
> > >> > feature "maximum" versions.
> > >> >
> > >> > > 9. One minor syntax fix: Note that here the "client" here may
be a
> > >> > producer
> > >> >
> > >> > (Kowshik): Great point! Done.
> > >> >
> > >> >
> > >> > Cheers,
> > >> > Kowshik
> > >> >
> > >> >
> > >> > On Tue, Mar 31, 2020 at 1:17 PM Boyang Chen <
> > reluctanthero104@gmail.com
> > >> >
> > >> > wrote:
> > >> >
> > >> > > Hey Kowshik,
> > >> > >
> > >> > > thanks for the revised KIP. Got a couple of questions:
> > >> > >
> > >> > > 1. "When is it safe for the brokers to begin handling EOS traffic"
> > >> could
> > >> > be
> > >> > > converted as "When is it safe for the brokers to start serving
new
> > >> > > Exactly-Once(EOS) semantics" since EOS is not explained earlier
in
> > the
> > >> > > context.
> > >> > >
> > >> > > 2. In the *Explanation *section, the metadata version number
part
> > >> seems a
> > >> > > bit blurred. Could you point a reference to later section that
we
> > >> going
> > >> > to
> > >> > > store it in Zookeeper and update it every time when there is
a
> > feature
> > >> > > change?
> > >> > >
> > >> > > 3. For the feature downgrade, although it's a Non-goal of the
KIP,
> > for
> > >> > > features such as group coordinator semantics, there is no legal
> > >> scenario
> > >> > to
> > >> > > perform a downgrade at all. So having downgrade door open is
> pretty
> > >> > > error-prone as human faults happen all the time. I'm assuming
as
> new
> > >> > > features are implemented, it's not very hard to add a flag during
> > >> feature
> > >> > > creation to indicate whether this feature is "downgradable".
Could
> > you
> > >> > > explain a bit more on the extra engineering effort for shipping
> this
> > >> KIP
> > >> > > with downgrade protection in place?
> > >> > >
> > >> > > 4. "Each broker’s supported dictionary of feature versions
will be
> > >> > defined
> > >> > > in the broker code." So this means in order to restrict a certain
> > >> > feature,
> > >> > > we need to start the broker first and then send a feature gating
> > >> request
> > >> > > immediately, which introduces a time gap and the intended-to-close
> > >> > feature
> > >> > > could actually serve request during this phase. Do you think
we
> > should
> > >> > also
> > >> > > support configurations as well so that admin user could freely
> roll
> > >> up a
> > >> > > cluster with all nodes complying the same feature gating, without
> > >> > worrying
> > >> > > about the turnaround time to propagate the message only after
the
> > >> cluster
> > >> > > starts up?
> > >> > >
> > >> > > 5. "adding a new Feature, updating or deleting an existing
> Feature",
> > >> may
> > >> > be
> > >> > > I misunderstood something, I thought the features are defined
in
> > >> broker
> > >> > > code, so admin could not really create a new feature?
> > >> > >
> > >> > > 6. I think we need a separate error code like
> > >> FEATURE_UPDATE_IN_PROGRESS
> > >> > to
> > >> > > reject a concurrent feature update request.
> > >> > >
> > >> > > 7. I think we haven't discussed the alternative solution to pass
> the
> > >> > > feature information through Zookeeper. Is that mentioned in the
> KIP
> > to
> > >> > > justify why using UpdateMetadata is more favorable?
> > >> > >
> > >> > > 8. I was under the impression that user could configure a range
of
> > >> > > supported versions, what's the trade-off for allowing single
> > finalized
> > >> > > version only?
> > >> > >
> > >> > > 9. One minor syntax fix: Note that here the "client" here may
be a
> > >> > producer
> > >> > >
> > >> > > Boyang
> > >> > >
> > >> > > On Mon, Mar 30, 2020 at 4:53 PM Colin McCabe <cmccabe@apache.org>
> > >> wrote:
> > >> > >
> > >> > > > On Thu, Mar 26, 2020, at 19:24, Kowshik Prakasam wrote:
> > >> > > > > Hi Colin,
> > >> > > > >
> > >> > > > > Thanks for the feedback! I've changed the KIP to address
your
> > >> > > > > suggestions.
> > >> > > > > Please find below my explanation. Here is a link to
KIP 584:
> > >> > > > >
> > >> > > >
> > >> > >
> > >> >
> > >>
> >
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-584%3A+Versioning+scheme+for+features
> > >> > > > > .
> > >> > > > >
> > >> > > > > 1. '__data_version__' is the version of the finalized
feature
> > >> > metadata
> > >> > > > > (i.e. actual ZK node contents), while the '__schema_version__'
> > is
> > >> the
> > >> > > > > version of the schema of the data persisted in ZK.
These serve
> > >> > > different
> > >> > > > > purposes. '__data_version__' is is useful mainly to
clients
> > during
> > >> > > reads,
> > >> > > > > to differentiate between the 2 versions of eventually
> consistent
> > >> > > > 'finalized
> > >> > > > > features' metadata (i.e. larger metadata version is
more
> > recent).
> > >> > > > > '__schema_version__' provides an additional degree
of
> > flexibility,
> > >> > > where
> > >> > > > if
> > >> > > > > we decide to change the schema for '/features' node
in ZK (in
> > the
> > >> > > > future),
> > >> > > > > then we can manage broker roll outs suitably (i.e.
> > >> > > > > serialization/deserialization of the ZK data can be
handled
> > >> safely).
> > >> > > >
> > >> > > > Hi Kowshik,
> > >> > > >
> > >> > > > If you're talking about a number that lets you know if data
is
> > more
> > >> or
> > >> > > > less recent, we would typically call that an epoch, and
not a
> > >> version.
> > >> > > For
> > >> > > > the ZK data structures, the word "version" is typically
reserved
> > for
> > >> > > > describing changes to the overall schema of the data that
is
> > >> written to
> > >> > > > ZooKeeper.  We don't even really change the "version" of
those
> > >> schemas
> > >> > > that
> > >> > > > much, since most changes are backwards-compatible.  But
we do
> > >> include
> > >> > > that
> > >> > > > version field just in case.
> > >> > > >
> > >> > > > I don't think we really need an epoch here, though, since
we can
> > >> just
> > >> > > look
> > >> > > > at the broker epoch.  Whenever the broker registers, its
epoch
> > will
> > >> be
> > >> > > > greater than the previous broker epoch.  And the newly
> registered
> > >> data
> > >> > > will
> > >> > > > take priority.  This will be a lot simpler than adding a
> separate
> > >> epoch
> > >> > > > system, I think.
> > >> > > >
> > >> > > > >
> > >> > > > > 2. Regarding admin client needing min and max information
-
> you
> > >> are
> > >> > > > right!
> > >> > > > > I've changed the KIP such that the Admin API also allows
the
> > user
> > >> to
> > >> > > read
> > >> > > > > 'supported features' from a specific broker. Please
look at
> the
> > >> > section
> > >> > > > > "Admin API changes".
> > >> > > >
> > >> > > > Thanks.
> > >> > > >
> > >> > > > >
> > >> > > > > 3. Regarding the use of `long` vs `Long` - it was not
> > deliberate.
> > >> > I've
> > >> > > > > improved the KIP to just use `long` at all places.
> > >> > > >
> > >> > > > Sounds good.
> > >> > > >
> > >> > > > >
> > >> > > > > 4. Regarding kafka.admin.FeatureCommand tool - you
are right!
> > I've
> > >> > > > updated
> > >> > > > > the KIP sketching the functionality provided by this
tool,
> with
> > >> some
> > >> > > > > examples. Please look at the section "Tooling support
> examples".
> > >> > > > >
> > >> > > > > Thank you!
> > >> > > >
> > >> > > >
> > >> > > > Thanks, Kowshik.
> > >> > > >
> > >> > > > cheers,
> > >> > > > Colin
> > >> > > >
> > >> > > > >
> > >> > > > >
> > >> > > > > Cheers,
> > >> > > > > Kowshik
> > >> > > > >
> > >> > > > > On Wed, Mar 25, 2020 at 11:31 PM Colin McCabe <
> > cmccabe@apache.org
> > >> >
> > >> > > > wrote:
> > >> > > > >
> > >> > > > > > Thanks, Kowshik, this looks good.
> > >> > > > > >
> > >> > > > > > In the "Schema" section, do we really need both
> > >> __schema_version__
> > >> > > and
> > >> > > > > > __data_version__?  Can we just have a single version
field
> > here?
> > >> > > > > >
> > >> > > > > > Shouldn't the Admin(Client) function have some
way to get
> the
> > >> min
> > >> > and
> > >> > > > max
> > >> > > > > > information that we're exposing as well?  I guess
we could
> > have
> > >> > min,
> > >> > > > max,
> > >> > > > > > and current.  Unrelated: is the use of Long rather
than long
> > >> > > deliberate
> > >> > > > > > here?
> > >> > > > > >
> > >> > > > > > It would be good to describe how the command line
tool
> > >> > > > > > kafka.admin.FeatureCommand will work.  For example
the flags
> > >> that
> > >> > it
> > >> > > > will
> > >> > > > > > take and the output that it will generate to STDOUT.
> > >> > > > > >
> > >> > > > > > cheers,
> > >> > > > > > Colin
> > >> > > > > >
> > >> > > > > >
> > >> > > > > > On Tue, Mar 24, 2020, at 17:08, Kowshik Prakasam
wrote:
> > >> > > > > > > Hi all,
> > >> > > > > > >
> > >> > > > > > > I've opened KIP-584
> <https://issues.apache.org/jira/browse/KIP-584>
> > >> <https://issues.apache.org/jira/browse/KIP-584> <
> > >> > https://issues.apache.org/jira/browse/KIP-584
> > >> > > >
> > >> > > > > > > which
> > >> > > > > > > is intended to provide a versioning scheme
for features.
> I'd
> > >> like
> > >> > > to
> > >> > > > use
> > >> > > > > > > this thread to discuss the same. I'd appreciate
any
> feedback
> > >> on
> > >> > > this.
> > >> > > > > > > Here
> > >> > > > > > > is a link to KIP-584
> <https://issues.apache.org/jira/browse/KIP-584>
> > >> <https://issues.apache.org/jira/browse/KIP-584>:
> > >> > > > > > >
> > >> > > > > >
> > >> > > >
> > >> > >
> > >> >
> > >>
> >
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-584%3A+Versioning+scheme+for+features
> > >> > > > > > >  .
> > >> > > > > > >
> > >> > > > > > > Thank you!
> > >> > > > > > >
> > >> > > > > > >
> > >> > > > > > > Cheers,
> > >> > > > > > > Kowshik
> > >> > > > > > >
> > >> > > > > >
> > >> > > > >
> > >> > > >
> > >> > >
> > >> >
> > >>
> > >
> >
>

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