Hi Calvin, 01. Should we update the KIP to mention this?
09. The upgrade part is still not very clear in my opinion. It would be good to clearly mention how we are going to handle the upgrade of the AlterPartition API and the Fetch API. For the former, the broker uses the ApiVersions API to discover the supported versions of the controller so it will use the appropriate version based on this. For the later, we use the IBP/metadata version to gate the version of the fetch request used. Therefore, the version 14 will be used only when the IBP/metadata version is upgraded. Besides those two points, the KIP looks good to me. Thanks, David On Fri, Feb 10, 2023 at 7:47 PM Calvin Liu <ca...@confluent.io.invalid> wrote: > Hi David, > 01. It is a good idea to fence some delayed Fetch requests from the reboot > followers. > 06. Ack > 09. Rephrased the sentence to let the ZK controller ignore the broker > epoch. > > Thanks, > Calvin. > > On Fri, Feb 10, 2023 at 6:11 AM David Jacot <dja...@confluent.io.invalid> > wrote: > > > Hi Calvin, > > > > 01. Yeah, this should generally not happen. I was wondering if it could > > happen in the case of a partial failure of a broker for instance. > > Generally, I think that being defensive on the leader side does not hurt > > here. I am perhaps too extreme here. > > > > 03. NewIsr does not need to be ignorable because we will only set it when > > an old version is used. > > > > 06. It is a bit weird to have ReplicaId and BrokerId in the final > schema. I > > would remove ReplicaId. The comment is enough to explain the renaming. > > > > 09. Could you elaborate on "As the AlterPartition and Fetch requests are > > shared between ZK and Kraft mode, the related field will keep empty in ZK > > mode and will not be used."? I would do it the other way around, I think > > that the followers and the leader should always populare all the fields > but > > the ZK controller should not take it into account. It will be easier like > > this vs having to put gates everywhere. > > > > Best, > > David > > > > On Thu, Feb 9, 2023 at 7:27 PM Calvin Liu <ca...@confluent.io.invalid> > > wrote: > > > > > Hi Alexandre, > > > 104: I am not aware of any proposals around the up-to-date replica > > > election. It can be a good place to dig deeper. > > > 105: Yes, it almost puts nothing on the performance. > > > > > > Thanks, > > > Calvin > > > > > > On Thu, Feb 9, 2023 at 1:26 AM Alexandre Dupriez < > > > alexandre.dupr...@gmail.com> wrote: > > > > > > > Hi, Calvin, > > > > > > > > Many thanks for the replies. > > > > > > > > 103. Thanks for confirming the testing strategy. Exercising the right > > > > sequence of requests is a good idea. > > > > > > > > 104. Out of scope here, but the KIP reminds that currently, the > > > > controller does not attempt to detect data loss on the latest replica > > > > in the ISR and to choose the most up-to-date replica as a leader. Is > > > > this an area where the community wants to invest in building a > > > > potential solution? > > > > > > > > 105. I assume any performance impact of the change in Fetch requests > > > > is marginal if even noticeable at all. > > > > > > > > Thanks, > > > > Alexandre > > > > > > > > Le mer. 8 févr. 2023 à 23:57, Calvin Liu <ca...@confluent.io.invalid > > > > a > > > > écrit : > > > > > > > > > > For Jun: > > > > > --- Since this KIP changes the inter-broker protocol, should we > bump > > up > > > > the > > > > > metadata version (the equivalent of IBP) during the upgrade? > > > > > Yes, we can. > > > > > > > > > > For Artem: > > > > > --- Could you elaborate on the behavior during rolls in the > > > Compatibility > > > > > section? > > > > > We can update the metadata version(IBP) to make sure the brokers > can > > > have > > > > > the latest code. > > > > > Also, during the IBP upgrade, the leader can just skip setting > broker > > > > epoch > > > > > or set -1 for the brokers that have not started using the new APIs. > > The > > > > > controller can bypass the check for such brokers so that the > cluster > > > can > > > > > still change ISR during the upgrade. > > > > > > > > > > --- Also for compatibility it's probably going to be easier to just > > > add a > > > > > new > > > > > array of epochs in addition to the existing array of broker ids, > > > instead > > > > of > > > > > removing one field and adding another. > > > > > We can do it both ways. Just prefer to replace it with a new field > > for > > > > > better readability. > > > > > > > > > > --- The KIP mentions that we would explicitly do something special > in > > > ZK > > > > > mode > > > > > in order to not implement new functionality. > > > > > It can be as simple as skipping setting the broker epoch if it is > in > > ZK > > > > > mode. > > > > > > > > > > For Alexandre: > > > > > 100: Yes, you are right, it does not require a controller > movement. I > > > > > removed the controller movement part when quoting the scenario from > > the > > > > > KAFKA-14139. > > > > > 101: In the current code, you can't remove the last replica in the > > ISR. > > > > > But, any damage to this replica will result in data loss. > > > > > 102: Yeah, I understand your concern. It is definitely great to > have > > a > > > > fix > > > > > in ZK, but considering the KAFKA-14139 is a rare case, it has > higher > > > ROE > > > > > for applying to just Kraft mode. > > > > > 103: I found that it is much easier to repro the bug in Kraft mode > by > > > > > feeding the controller with a given sequence of events/requests. So > > we > > > > may > > > > > just need a unit test to cover the case. > > > > > > > > > > For David: > > > > > 01: > > > > > Can you help explain why the follower can have a stale broker > epoch? > > Is > > > > it > > > > > because the registration request has any delay? But the broker will > > not > > > > > start fetching before the registration success. > > > > > On the other hand, if the follower fetches with the stale broker > > epoch, > > > > is > > > > > it good enough to ask the leader to hold to include this follower > > until > > > > the > > > > > fetch is consistent with the metadata cache? > > > > > 02: Ack > > > > > 03: I think NewIsrWithEpochs is not ignorable. For the deprecated > > > > > field NewIsr, what is the right way to make it ignorable? Just mark > > it > > > > > ignorable in this change? > > > > > 04: Ack > > > > > 05: Ack > > > > > 06: Ack > > > > > 07: Yes, will add it. > > > > > > > > > > > > > > > > > > > > On Wed, Feb 8, 2023 at 6:52 AM David Jacot > > <dja...@confluent.io.invalid > > > > > > > > > wrote: > > > > > > > > > > > Hi Calvin, > > > > > > > > > > > > Thanks for the KIP! The overall approach looks reasonable to me. > I > > > > have a > > > > > > few questions/comments: > > > > > > > > > > > > 01. I wonder if the leader should also verify the broker epochs > > based > > > > on > > > > > > its metadata cache before sending the AlterPartition request to > the > > > > > > controller. Imagine the case where a follower not in the ISR > would > > > keep > > > > > > fetching with a stale broker epoch but with a valid leader epoch. > > In > > > > this > > > > > > case, the leader would try to add it back to the ISR when the > > > follower > > > > > > catches up but the controller would reject it because its broker > > > epoch > > > > is > > > > > > stale. Until this condition resolves itself, the leader can't add > > any > > > > other > > > > > > followers back to the ISR because the ISR validation is all or > > > nothing > > > > at > > > > > > the moment. Letting the leader check before sending the > > > AlterPartition > > > > > > request would mitigate this. This condition must be rare but > could > > > > happen. > > > > > > We did this in KIP-841. > > > > > > > > > > > > 02. In AlterPartitionRequest/AlterPartitionResponse, you need to > > > > update the > > > > > > `validVersions` to `0-3`. > > > > > > > > > > > > 03. Personally, I like the `NewIsrWithEpochs` field in > > > > > > the AlterPartitionRequest. We can handle the backward > compatibility > > > in > > > > the > > > > > > request builder. Basically, we would always populate > > NewIsrWithEpochs > > > > and > > > > > > the request builder can translate it to NewIsr if an earlier > > version > > > is > > > > > > used. Should the field be ignorable? > > > > > > > > > > > > 04. Should NewIsrWithEpochs.BrokerEpoch have -1 as default? > > > > > > > > > > > > 05. In FetchRequest/FetchResponse, you need to update the > > > > `validVersions` > > > > > > as well. > > > > > > > > > > > > 06. It is a little weird to have ReplicaId and BrokerEpoch in the > > > > > > FetchRequest. I wonder if we should rename ReplicaId to BrokerId > > > > because it > > > > > > is actually the broker id (even the documentation of the field > says > > > > it). > > > > > > > > > > > > 07. On the followers, the fetch request version is derived from > the > > > > > > metadata version/IBP. As we add a new fetch version, we need to > > add a > > > > new > > > > > > metadata version/IBP as well. > > > > > > > > > > > > 08. Regarding KRaft vs ZK, I don't have a strong opinion. ZK is > on > > > the > > > > way > > > > > > out so not doing it seems fine. If we do this, we could basically > > > just > > > > > > ignore the broker epoch in ZK and it will keep working as today. > > > > > > > > > > > > Best, > > > > > > David > > > > > > > > > > > > On Wed, Feb 8, 2023 at 3:01 PM Alexandre Dupriez < > > > > > > alexandre.dupr...@gmail.com> wrote: > > > > > > > > > > > > > Hi, Calvin, > > > > > > > > > > > > > > Thanks for the KIP and fast follow-up. A few questions. > > > > > > > > > > > > > > 100. The scenario illustrated in the KIP involves a controller > > > > > > > movement. Is this really required? Cannot the scenario occur > > with a > > > > > > > similar stale AlterPartition request and the same controller > > > > > > > throughout? > > > > > > > > > > > > > > 101. In the case where card(ISR) = 1 and the last replica > leaves, > > > it > > > > > > > will be re-elected as the leader upon reconnection. If the > > replica > > > is > > > > > > > empty, all data for the partition will be lost. Is this a > correct > > > > > > > understanding of the scenario? > > > > > > > > > > > > > > 102. I understand that ZK is going to be unsupported soon. > > However > > > > for > > > > > > > as long as it is available to end users, is there any reason > not > > to > > > > > > > support the fix in ZK mode? Arguably, the implementation for > the > > > > logic > > > > > > > to AlterPartition is duplicated for both controller types, and > it > > > may > > > > > > > be more work than is worth if ZK is fully decommissioned in the > > > next > > > > > > > few months. (Alternatively, is there a plan to back port the > fix > > to > > > > > > > older minor versions?). > > > > > > > > > > > > > > 103. The KIP mentions system tests to be used to simulate the > > race > > > > > > > condition. Would it be possible to provide more details about > it? > > > Do > > > > > > > we think it worth having this scenario be exercised in the > > > functional > > > > > > > tests of the core/server module? > > > > > > > > > > > > > > Thanks, > > > > > > > Alexandre > > > > > > > > > > > > > > Le mer. 8 févr. 2023 à 03:31, Artem Livshits > > > > > > > <alivsh...@confluent.io.invalid> a écrit : > > > > > > > > > > > > > > > > Hi Calvin, > > > > > > > > > > > > > > > > Thank you for the KIP. I have a similar question -- we need > to > > > > support > > > > > > > > rolling upgrades (when we have some old brokers and some new > > > > brokers), > > > > > > so > > > > > > > > there could be combinations of old leader - new follower, new > > > > leader - > > > > > > > old > > > > > > > > follower, new leader - old controller, old leader - new > > > controller. > > > > > > > Could > > > > > > > > you elaborate on the behavior during rolls in the > Compatibility > > > > > > section? > > > > > > > > > > > > > > > > Also for compatibility it's probably going to be easier to > just > > > > add a > > > > > > new > > > > > > > > array of epochs in addition to the existing array of broker > > ids, > > > > > > instead > > > > > > > of > > > > > > > > removing one field and adding another. > > > > > > > > > > > > > > > > The KIP mentions that we would explicitly do something > special > > in > > > > ZK > > > > > > mode > > > > > > > > in order to not implement new functionality. I think it may > be > > > > easier > > > > > > to > > > > > > > > implement functionality for both ZK and KRraft mode than > adding > > > > code to > > > > > > > > disable it in ZK mode. > > > > > > > > > > > > > > > > -Artem > > > > > > > > > > > > > > > > On Tue, Feb 7, 2023 at 4:58 PM Jun Rao > > <j...@confluent.io.invalid > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > Hi, Calvin, > > > > > > > > > > > > > > > > > > Thanks for the KIP. Looks good to me overall. > > > > > > > > > > > > > > > > > > Since this KIP changes the inter-broker protocol, should we > > > bump > > > > up > > > > > > the > > > > > > > > > metadata version (the equivalent of IBP) during upgrade? > > > > > > > > > > > > > > > > > > Jun > > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Feb 3, 2023 at 10:55 AM Calvin Liu > > > > > > <ca...@confluent.io.invalid > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > Hi everyone, > > > > > > > > > > I'd like to discuss the fix for the broker reboot data > loss > > > > > > > KAFKA-14139 > > > > > > > > > > <https://issues.apache.org/jira/browse/KAFKA-14139>. > > > > > > > > > > It changes the Fetch and AlterPartition requests to > include > > > the > > > > > > > broker > > > > > > > > > > epochs. Then the controller can use these epochs to help > > > > reject the > > > > > > > stale > > > > > > > > > > AlterPartition request. > > > > > > > > > > Please take a look. Thanks! > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-903%3A+Replicas+with+stale+broker+epoch+should+not+be+allowed+to+join+the+ISR > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
