Hi PoAn,
As we are getting closer to releasing 4.0, I think that we can resume
working on this one if you are still interested. Are you? I would like
to have it in 4.1.
Best,
David
On Wed, Jan 15, 2025 at 1:26 AM Kirk True <k...@kirktrue.pro> wrote:
>
> Hi all,
>
> Hopefully a quick question...
>
> KT01. Will clients calculate the topic hash on the client? Based on the
> current state of the KIP and PR, I would have thought "no", but I ask based
> on the discussion around the possible use of Guava on client.
>
> Thanks,
> Kirk
>
> On Mon, Jan 6, 2025, at 9:11 AM, David Jacot wrote:
> > Hi PoAn,
> >
> > Thanks for the update. I haven't read the updated KIP yet.
> >
> > DJ02: I am not sure about using Guava as a dependency. I mentioned it more
> > as an inspiration/reference. I suppose that we could use it on the server
> > but we should definitely not use it on the client. I am not sure how others
> > feel about it.
> >
> > Best,
> > David
> >
> > On Mon, Jan 6, 2025 at 5:21 AM PoAn Yang <yangp...@gmail.com> wrote:
> >
> > > Hi Chia-Ping / David / Lucas,
> > >
> > > Happy new year and thanks for the review.
> > >
> > > DJ02: Thanks for the suggestion. I updated the PR to use Guava.
> > >
> > > DJ03: Yes, I updated the description to mention ISR change,
> > > add altering partition reassignment case, and mention that
> > > non-related topic change doesn’t trigger a rebalance.
> > > DJ03.1: Yes, I will keep using ModernGroup#requestMetadataRefresh
> > > to notify group.
> > >
> > > DJ06: Updated the PR to use Guava Hashing#combineUnordered
> > > function to combine topic hash.
> > >
> > > DJ07: Renamed it to MetadataHash.
> > >
> > > DJ08: Added a sample hash function to the KIP and use first byte as magic
> > > byte. This is also included in latest PR.
> > >
> > > DJ09: Added two paragraphs about upgraded and downgraded.
> > >
> > > DJ10: According to Lucas’s comment, I add StreamsGroupMetadataValue update
> > > to this KIP.
> > >
> > > Thanks,
> > > PoAn
> > >
> > >
> > > > On Dec 20, 2024, at 3:58 PM, Chia-Ping Tsai <chia7...@gmail.com> wrote:
> > > >
> > > >> because assignors are sticky.
> > > >
> > > > I forgot about that spec again :(
> > > >
> > > >
> > > >
> > > >
> > > > David Jacot <david.ja...@gmail.com> 於 2024年12月20日 週五 下午3:41寫道：
> > > >
> > > >> Hi Chia-Ping,
> > > >>
> > > >> DJ08: In my opinion, changing the format will be rare so it is
> > > >> acceptable if rebalances are triggered in this case on
> > > >> upgrade/downgrade. It is also what will happen if a cluster is
> > > >> downgraded from 4.1 (with this KIP) to 4.0. The rebalance won't change
> > > >> anything if the topology of the group is the same because assignors
> > > >> are sticky. The default ones are and we recommend custom ones to also
> > > >> be.
> > > >>
> > > >> Best,
> > > >> David
> > > >>
> > > >> On Fri, Dec 20, 2024 at 2:11 AM Chia-Ping Tsai <chia7...@apache.org>
> > > >> wrote:
> > > >>>
> > > >>> ummm, it does not work for downgrade as the old coordinator has no
> > > >>> idea
> > > >> about new format :(
> > > >>>
> > > >>>
> > > >>> On 2024/12/20 00:57:27 Chia-Ping Tsai wrote:
> > > >>>> hi David
> > > >>>>
> > > >>>>> DJ08:
> > > >>>>
> > > >>>> That's a good question. If the "hash" lacks version control, it could
> > > >> trigger a series of unnecessary rebalances. However, adding additional
> > > >> information ("magic") to the hash does not help the upgraded
> > > >> coordinator
> > > >> determine the "version." This means that the upgraded coordinator would
> > > >> still trigger unnecessary rebalances because it has no way to know
> > > >> which
> > > >> format to use when comparing the hash.
> > > >>>>
> > > >>>> Perhaps we can add a new field to ConsumerGroupMetadataValue to
> > > >> indicate the version of the "hash." This would allow the coordinator,
> > > when
> > > >> handling subscription metadata, to compute the old hash and determine
> > > >> whether an epoch bump is necessary. Additionally, the coordinator can
> > > >> generate a new record to upgrade the hash without requiring an epoch
> > > bump.
> > > >>>>
> > > >>>> Another issue is whether the coordinator should cache all versions of
> > > >> the hash. I believe this is necessary; otherwise, during an upgrade,
> > > there
> > > >> would be extensive recomputing of old hashes.
> > > >>>>
> > > >>>> I believe this idea should also work for downgrades, and that's just
> > > >> my two cents.
> > > >>>>
> > > >>>> Best,
> > > >>>> Chia-Ping
> > > >>>>
> > > >>>>
> > > >>>> On 2024/12/19 14:39:41 David Jacot wrote:
> > > >>>>> Hi PoAn and Chia-Ping,
> > > >>>>>
> > > >>>>> Thanks for your responses.
> > > >>>>>
> > > >>>>> DJ02: Sorry, I was not clear. I was wondering whether we could
> > > >> compute the
> > > >>>>> hash without having to convert to bytes before. Guava has a nice
> > > >> interface
> > > >>>>> for this allowing to incrementally add primitive types to the hash.
> > > >> We can
> > > >>>>> discuss this in the PR as it is an implementation detail.
> > > >>>>>
> > > >>>>> DJ03: Thanks. I don't think that the replicas are updated when a
> > > >> broker
> > > >>>>> shuts down. What you said applies to the ISR. I suppose that we can
> > > >> rely on
> > > >>>>> the ISR changes to trigger updates. It is also worth noting
> > > >>>>> that TopicsDelta#changedTopics is updated for every change (e.g. ISR
> > > >>>>> change, leader change, replicas change, etc.). I suppose that it is
> > > >> OK but
> > > >>>>> it seems that it will trigger refreshes which are not necessary.
> > > >> However, a
> > > >>>>> rebalance won't be triggered because the hash won't change.
> > > >>>>> DJ03.1: I suppose that we will continue to rely on
> > > >>>>> ModernGroup#requestMetadataRefresh to notify groups that must
> > > >> refresh their
> > > >>>>> hashes. Is my understanding correct?
> > > >>>>>
> > > >>>>> DJ05: Fair enough.
> > > >>>>>
> > > >>>>> DJ06: You mention in two places that you would like to combine
> > > >> hashes by
> > > >>>>> additioning them. I wonder if this is a good practice. Intuitively,
> > > >> I would
> > > >>>>> have used XOR or hashed the hashed. Guava has a method for combining
> > > >>>>> hashes. It may be worth looking into the algorithm used.
> > > >>>>>
> > > >>>>> DJ07: I would rename "AllTopicHash" to "MetadataHash" in order to be
> > > >> more
> > > >>>>> generic.
> > > >>>>>
> > > >>>>> DJ08: Regarding the per topic hash, I wonder whether we should
> > > >> precise in
> > > >>>>> the KIP how we will compute it. I had the following in mind:
> > > >>>>> hash(topicName; numPartitions; [partitionId;sorted racks]). We could
> > > >> also
> > > >>>>> add a magic byte at the first element as a sort of version. I am not
> > > >> sure
> > > >>>>> whether it is needed though. I was thinking about this while
> > > >> imagining how
> > > >>>>> we would handle changing the format in the future.
> > > >>>>>
> > > >>>>> DJ09: It would be great if we could provide more details about
> > > >> backward
> > > >>>>> compatibility. What happens when the cluster is upgraded or
> > > >> downgraded?
> > > >>>>>
> > > >>>>> DJ10: We should update KIP-1071. It may be worth pigging them in the
> > > >>>>> discussion thread of KIP-1071.
> > > >>>>>
> > > >>>>> Best,
> > > >>>>> David
> > > >>>>>
> > > >>>>> On Tue, Dec 17, 2024 at 9:25 AM PoAn Yang <yangp...@gmail.com>
> > > >> wrote:
> > > >>>>>
> > > >>>>>> Hi Chia-Ping / David / Andrew,
> > > >>>>>>
> > > >>>>>> Thanks for the review and suggestions.
> > > >>>>>>
> > > >>>>>> DJ01: Removed all implementation details.
> > > >>>>>>
> > > >>>>>> DJ02: Does the “incrementally” mean that we only calculate the
> > > >> difference
> > > >>>>>> parts?
> > > >>>>>> For example, if the number of partition change, we only calculate
> > > >> the hash
> > > >>>>>> of number of partition and reconstruct it to the topic hash.
> > > >>>>>> IMO, we only calculate topic hash one time. With cache mechanism,
> > > >> the
> > > >>>>>> value can be reused in different groups on a same broker.
> > > >>>>>> The CPU usage for this part is not very high.
> > > >>>>>>
> > > >>>>>> DJ03: Added the update path to KIP for both cases.
> > > >>>>>>
> > > >>>>>> DJ04: Yes, it’s a good idea. With cache mechanism and single hash
> > > >> per
> > > >>>>>> group, we can balance cpu and disk usage.
> > > >>>>>>
> > > >>>>>> DJ05: Currently, the topic hash is only used in coordinator.
> > > >> However, the
> > > >>>>>> metadata image is used in many different places.
> > > >>>>>> How about we move the hash to metadata image when we find more use
> > > >> cases?
> > > >>>>>>
> > > >>>>>> AS1, AS2: Thanks for the reminder. I will simply delete
> > > >>>>>> ShareGroupPartitionMetadataKey/Value and add a new field to
> > > >>>>>> ShareGroupMetadataValue.
> > > >>>>>>
> > > >>>>>> Best,
> > > >>>>>> PoAn
> > > >>>>>>
> > > >>>>>>> On Dec 17, 2024, at 5:50 AM, Andrew Schofield <
> > > >>>>>> andrew_schofield_j...@outlook.com> wrote:
> > > >>>>>>>
> > > >>>>>>> Hi PoAn,
> > > >>>>>>> Thanks for the KIP.
> > > >>>>>>>
> > > >>>>>>> AS1: From the point of view of share groups, the API and record
> > > >> schema
> > > >>>>>>> definitions are unstable in AK 4.0. In AK 4.1, we will start
> > > >> supporting
> > > >>>>>> proper
> > > >>>>>>> versioning. As a result, I think you do not need to deprecate
> > > >> the fields
> > > >>>>>> in the
> > > >>>>>>> ShareGroupPartitionMetadataValue. Just include the schema for
> > > >> the fields
> > > >>>>>>> which are actually needed, and I'll update the schema in the
> > > >> code when
> > > >>>>>>> the KIP is implemented.
> > > >>>>>>>
> > > >>>>>>> AS2: In the event that DJ04 actually removes the need for
> > > >>>>>>> ConsumerGroupPartitionMetadataKey/Value entirely, I would simply
> > > >>>>>>> delete ShareGroupPartitionMetadataKey/Value, assuming that it is
> > > >>>>>>> accepted in time for AK 4.1.
> > > >>>>>>>
> > > >>>>>>>
> > > >>>>>>> Thanks,
> > > >>>>>>> Andrew
> > > >>>>>>> ________________________________________
> > > >>>>>>> From: Chia-Ping Tsai <chia7...@apache.org>
> > > >>>>>>> Sent: 16 December 2024 16:27
> > > >>>>>>> To: dev@kafka.apache.org <dev@kafka.apache.org>
> > > >>>>>>> Subject: Re: [DISCUSS] KIP-1101: Trigger rebalance on rack
> > > >> topology
> > > >>>>>> changes
> > > >>>>>>>
> > > >>>>>>> hi David
> > > >>>>>>>
> > > >>>>>>>> DJ05
> > > >>>>>>>
> > > >>>>>>> One of the benefits of having a single hash per group (DJ04) is
> > > >> the
> > > >>>>>> reduction in the size of stored data. Additionally, the cost of
> > > >>>>>> re-computing can be minimized thanks to caching. So I'm + 1 to
> > > >> DJ04.
> > > >>>>>> However, the advantage of storing the topic cache in the metadata
> > > >> image is
> > > >>>>>> somewhat unclear to me. Could you please provide more details on
> > > >> what you
> > > >>>>>> mean by "tight"?Furthermore, since the metadata image is a
> > > >> thread-safe
> > > >>>>>> object, we need to ensure that the lazy initialization is also
> > > >> thread-safe.
> > > >>>>>> If no other components require the cache, it would be better to
> > > >> keep the
> > > >>>>>> caches within the coordinator.
> > > >>>>>>>
> > > >>>>>>> Best,
> > > >>>>>>> Chia-Ping
> > > >>>>>>>
> > > >>>>>>> On 2024/12/16 14:01:35 David Jacot wrote:
> > > >>>>>>>> Hi PoAn,
> > > >>>>>>>>
> > > >>>>>>>> Thanks for the KIP. I have some comments about it.
> > > >>>>>>>>
> > > >>>>>>>> DJ01: Please, remove all the code from the KIP. We only care
> > > >> about
> > > >>>>>> public
> > > >>>>>>>> interface changes, not about implementation details.
> > > >>>>>>>> DJ02: Regarding the hash computation, I agree that we should use
> > > >>>>>> Murmur3.
> > > >>>>>>>> However, I don't quite like the implementation that you shared.
> > > >> I
> > > >>>>>> wonder if
> > > >>>>>>>> we could make it work incrementally instead of computing a hash
> > > >> of
> > > >>>>>>>> everything and combining them.
> > > >>>>>>>> DJ03: Regarding the cache, my understanding is that the cache is
> > > >>>>>> populated
> > > >>>>>>>> when a topic without hash is seen in a HB request and the cache
> > > >> is
> > > >>>>>> cleaned
> > > >>>>>>>> up when topics are deleted based on the metadata image.
> > > >> However, the
> > > >>>>>> update
> > > >>>>>>>> path is not clear. Let's say that a partition is added to a
> > > >> topic, how
> > > >>>>>> does
> > > >>>>>>>> it detect it? Let's also imagine that the racks of a partition
> > > >> have
> > > >>>>>>>> changed, how does it detect it? In the KIP, it would be nice to
> > > >> be clear
> > > >>>>>>>> about those.
> > > >>>>>>>> DJ04: I wonder whether we should go with a single hash per
> > > >> group. Your
> > > >>>>>>>> argument against it is that it would require to re-compute the
> > > >> hash of
> > > >>>>>> all
> > > >>>>>>>> the topics when it needs to be computed. In my opinion, we could
> > > >>>>>> leverage
> > > >>>>>>>> the cached hash per topic to compute the hash of all the
> > > >> subscribed
> > > >>>>>> ones.
> > > >>>>>>>> We could basically combine all the hashes without having to
> > > >> compute all
> > > >>>>>> of
> > > >>>>>>>> them. This approach has a few benefits. 1) We could get rid of
> > > >>>>>>>> the ConsumerGroupPartitionMetadata record as we could store the
> > > >> hash
> > > >>>>>> with
> > > >>>>>>>> the group epoch. 2) We could get rid of the Map that we keep in
> > > >> each
> > > >>>>>> group
> > > >>>>>>>> to store the hashed corresponding to the subscribed topics.
> > > >>>>>>>> DJ05: Regarding the cache again, I wonder if we should actually
> > > >> store
> > > >>>>>> the
> > > >>>>>>>> hash in the metadata image instead of maintaining it somewhere
> > > >> else. We
> > > >>>>>>>> could still lazily compute it. The benefit is that the value
> > > >> would be
> > > >>>>>> tight
> > > >>>>>>>> to the topic. I have not really looked into it. Would it be an
> > > >> option?
> > > >>>>>>>>
> > > >>>>>>>> I'll be away for two weeks starting from Saturday. I kindly ask
> > > >> you to
> > > >>>>>> wait
> > > >>>>>>>> on me if we cannot conclude this week.
> > > >>>>>>>>
> > > >>>>>>>> Best,
> > > >>>>>>>> David
> > > >>>>>>>>
> > > >>>>>>>> On Tue, Nov 5, 2024 at 1:43 PM Frank Yang <yangp...@gmail.com>
> > > >> wrote:
> > > >>>>>>>>
> > > >>>>>>>>> Hi Chia-Ping,
> > > >>>>>>>>>
> > > >>>>>>>>> Thanks for the review and suggestions.
> > > >>>>>>>>>
> > > >>>>>>>>> Q0: Add how rack change and how it affects topic partition.
> > > >>>>>>>>>
> > > >>>>>>>>> Q1: Add why we need a balance algorithm to Motivation section.
> > > >>>>>>>>>
> > > >>>>>>>>> Q2: After checking again, we don’t need to update cache when
> > > >> we replay
> > > >>>>>>>>> records. We only need to renew it in consumer heartbeat.
> > > >>>>>>>>>
> > > >>>>>>>>> Q3: Add a new section “Topic Hash Function”.
> > > >>>>>>>>>
> > > >>>>>>>>> Thanks.
> > > >>>>>>>>> PoAn
> > > >>>>>>>>>
> > > >>>>>>>>>> On Nov 1, 2024, at 4:39 PM, Chia-Ping Tsai <
> > > >> chia7...@gmail.com>
> > > >>>>>> wrote:
> > > >>>>>>>>>>
> > > >>>>>>>>>> hi PoAn
> > > >>>>>>>>>>
> > > >>>>>>>>>> Thanks for for this KIP!
> > > >>>>>>>>>>
> > > >>>>>>>>>> Q0: Could you add more details about `A topic partition has
> > > >> rack
> > > >>>>>> change`?
> > > >>>>>>>>>> IIRC, the "rack change" includes both follower and leader,
> > > >> right?
> > > >>>>>>>>>>
> > > >>>>>>>>>> Q1: Could you please add the 'concerns' we discussed to the
> > > >> Motivation
> > > >>>>>>>>>> section? This should include topics like 'computations' and
> > > >> 'space
> > > >>>>>>>>> usage'.
> > > >>>>>>>>>>
> > > >>>>>>>>>> Q2: `The group coordinator can leverage it to add a new topic
> > > >>>>>> hash.`This
> > > >>>>>>>>>> description seems a bit off to me. Why do we need to update
> > > >> the cache
> > > >>>>>> at
> > > >>>>>>>>>> this phase? The cache is intended to prevent duplicate
> > > >> computations
> > > >>>>>>>>> caused
> > > >>>>>>>>>> by heartbeat requests that occur between two metadata change
> > > >> events.
> > > >>>>>>>>>> Therefore, we could even remove the changed topics from
> > > >> caches on a
> > > >>>>>>>>>> metadata change, as the first heartbeat request would update
> > > >> the
> > > >>>>>> caches
> > > >>>>>>>>> for
> > > >>>>>>>>>> all changed topics.
> > > >>>>>>>>>>
> > > >>>>>>>>>> Q3: Could you please include a section about the choice of
> > > >> hash
> > > >>>>>>>>>> implementation? The hash implementation must be consistent
> > > >> across
> > > >>>>>>>>> different
> > > >>>>>>>>>> JDKs, so we use Murmur3 to generate the hash value.
> > > >>>>>>>>>>
> > > >>>>>>>>>> Best,
> > > >>>>>>>>>> Chia-Ping
> > > >>>>>>>>>>
> > > >>>>>>>>>>
> > > >>>>>>>>>> Frank Yang <yangp...@gmail.com> 於 2024年11月1日 週五 下午3:57寫道：
> > > >>>>>>>>>>
> > > >>>>>>>>>>> Hi all,
> > > >>>>>>>>>>>
> > > >>>>>>>>>>> I would like to start a discussion thread on KIP-1101.
> > > >> Trigger
> > > >>>>>> rebalance
> > > >>>>>>>>>>> on rack topology changes. In this KIP, we aim to use less
> > > >> memory /
> > > >>>>>> disk
> > > >>>>>>>>>>> resources to detect rack changes in the new coordinator.
> > > >>>>>>>>>>>
> > > >>>>>>>>>>>
> > > >>>>>>>>>>>
> > > >>>>>>>>>
> > > >>>>>>
> > > >>
> > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-1101%3A+Trigger+rebalance+on+rack+topology+changes
> > > >>>>>>>>>>>
> > > >>>>>>>>>>> Please take a look and feel free to share any thoughts.
> > > >>>>>>>>>>>
> > > >>>>>>>>>>> Thanks.
> > > >>>>>>>>>>> PoAn
> > > >>>>>>>>>
> > > >>>>>>>>>
> > > >>>>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>
> > > >>>>
> > > >>
> > >
> > >
> >
