Hi Henry, Thanks for the response.
1. HC> Yes we only upload data logs to fast cloud storage. The follower broker will build up its own indexes, producer snapshot as it appends data records to its local logs (in the same way today when the follower builds up those indexing data structure when it is doing appendAsFollower from data from FetchResponse). This is different than KIP-405 where it needs to build up and upload all those index/snapshot files to object storage since all the data-logs/index-files will no longer be present on all brokers once local.retention.ms passed, the data files and its index files needs to live together on object storage for the future downloads. In our KIP, the fast object storage is merely an intermediate data hop to transfer data logs, both leader and followers have their data-logs and indexes built up and kept in the traditional way until the content is uploaded onto slow object storage. I see. We should add them into the KIP. 2. HC>. We sort of assume the AWS S3/S3E1Z will always be there but might have slower access time occasionally. In the rare case when the fast cloud storage is down, the replication flow from leader to the follower will be stalled. If the producer is producing is using acks=1, the ack will be sent back from the leader to the producer immediately, but the follower will not get the data immediately so the high watermark cannot move and the consumer won't be able to consumer that message. If the producer is using acks=all, the ack will not be able to sent back to the producer. I think we can use the proposal you had to fall back to the traditional FetchRequest/Response, that can come as the enhancement to this KIP as an error handling improvement. Yes, we should consider this situation and put in the KIP. 3. HC> Yes you are right that in 2 brokers with S3E1Z deploy there are only 2 AZs (although there are 5 replicas), so there is a tradeoff we lost the availability in 3rd AZ. If the user cares about durability and availability in all 3 AZs, they can choose to deploy with 3 brokers and the S3E1Z, this way they get durability and availability in all 3AZs but they still get the across-AZ traffic free. In our design, we put the leader and in the same AZ as the S3E1Z to speed up the upload of data segments. In our vision of this project, we can get rid of follower in the future if we can speed up the follower bootstrap/catchup time on leader switch. It's fine for this tradeoff. I just think we should clearly write in the KIP. About the WAL metadata: HC> Yes the Wal Metadata size can be big. In terms of the life cycle of WAL segment and its metadata, as soon as the log content is uploaded onto slow object storage, we can remove the data segment from fast object storage. For a large active topic, the log segment rotation and subsequent upload to slow object storage can happen within 5-10 minutes. But sometimes it might be hard to track each upload, a simpler implementation would be using topic's local.retention.ms to decide whether the wal segment and its metadata are still in scope, that retention time might be 1-2 hours. In terms of ratio of segment between KIP-405 and KIP-1176, we are aiming to upload every 10ms with data from multiple partitions. The upload size for the data segment is about 100KB-300KB, so the ratio is about 3000-10000 times. Our current thinking is to have a shorter retention on the wal metadata topic (e.g. 1-2 hours) to reduce the overall disk space for the metadata topic, but your other concern about 3-way replication of this metadata topic and the across-AZ traffic cost of that replication is still there, the data volume of this metadata topic is a small/medium size topic (our calculation shows it's about 200KB/s per broker node). Maybe we can also use S3E1Z to save the across-AZ traffic cost of the metadata topic replication? > a simpler implementation would be using topic's local.retention.ms to decide whether the wal segment and its metadata are still in scope, that retention time might be 1-2 hours. Sorry, I don't get the idea of using local.retention.ms config. Suppose " local.retention.ms" is 1 hour, are we going to delete the wal segment/metadata after 1 hour it's uploaded to fast cloud storage? That means we might delete the data that are still in the active segment (not rolled), right? Because we can't predict when the log segment rotation will happen, using local.retention.ms is not a good idea. Or do I misunderstand it? I understand the rationale why you choose to use internal topic to store the wal metadata. I just want to see how we can handle the size of the metadata well, either we have a good retention policy, or periodically upload to S3E1Z for checkpointing. No matter the ratio is 3000 or 10000, if the size will only get increased, not decreased, then when the broker restarted, the wal metadata consumer will need more and more time to read all the wal metadata before it can serve the produce request. That will be a problem sometime in the future. Thank you. Luke On Fri, May 9, 2025 at 5:52 AM Henry Haiying Cai <haiying_...@yahoo.com.invalid> wrote: > Luke, > Thanks for your continued suggestions on this KIP, see an my answer below > inline with HC> indentation. > On Thursday, May 8, 2025 at 02:10:07 AM PDT, Luke Chen < > show...@gmail.com> wrote: > > Hi Henry, > > Some more questions: > 2. It seems in the KIP, I _assume_ the fast cloud storage will always be > available without issue. > What will happen when the fast cloud storage is down? > Do we fail the producer write immediately? Or do we have any fall back > mechanism? > Maybe we can fall back to the traditional data replication like I proposed > earlier? > > HC>. We sort of assume the AWS S3/S3E1Z will always be there but might > have slower access time occasionally. In the rare case when the fast cloud > storage is down, the replication flow from leader to the follower will be > stalled. If the producer is producing is using acks=1, the ack will be > sent back from the leader to the producer immediately, but the follower > will not get the data immediately so the high watermark cannot move and the > consumer won't be able to consumer that message. If the producer is using > acks=all, the ack will not be able to sent back to the producer. I think > we can use the proposal you had to fall back to the traditional > FetchRequest/Response, that can come as the enhancement to this KIP as an > error handling improvement. > 3. Durability > In the KIP, we tried to propose the "2 brokers + S3E1Z" deployment, which > is quite attractive. > But I think we should make it clear about how the durability can be. > In 3 brokers deployment, we usually deploy 3 brokers in 3 different AZ for > durability or availability. > But in "2 brokers + S3E1Z" deployment, we should deploy them on 3 different > AZs, too, right? > However in your previous reply, you put the leader node and S3E1Z in the > same AZ, to trade for lower latency. > Do you think we should make it clear in the KIP to add an additional > "durability" section? > And I guess in the comparison table in the KIP, you also put the leader and > S3E1Z in the same zone to get the single digit ms, is that right? > We might need to add some more context about the deployment above the > comparison table. > > HC> Yes you are right that in 2 brokers with S3E1Z deploy there are only 2 > AZs (although there are 5 replicas), so there is a tradeoff we lost the > availability in 3rd AZ. If the user cares about durability and > availability in all 3 AZs, they can choose to deploy with 3 brokers and the > S3E1Z, this way they get durability and availability in all 3AZs but they > still get the across-AZ traffic free. In our design, we put the leader and > in the same AZ as the S3E1Z to speed up the upload of data segments. In > our vision of this project, we can get rid of follower in the future if we > can speed up the follower bootstrap/catchup time on leader switch. > Thank you. > Luke > > > > Thanks. > Luke > > On Thu, May 8, 2025 at 3:57 PM Luke Chen <show...@gmail.com> wrote: > > > Hi Xinyu and Henry, > > > > I think the WAL metadata in KIP1176 is not for log recover, the log > > recovery still loads log segments locally. > > The WAL metadata is for leader <-> follower information sharing only. Is > > my understanding correct? > > > > About the WAL metadata, as I mentioned earlier, I still worry about the > > size of it even if we move it to a separate topic. > > Since we don't know when exactly the WAL log segments will be moved to > > slow cloud storage, we have no way to set a "safe" retention.ms for this > > topic. > > Like in current tiered storage, by default we set retention.ms to -1 for > > the remote log metadata topic to avoid data loss. > > But we know the metadata size of KIP-405 VS KIP-1176 will have huge > > differences. > > Suppose the segment size is 1GB, and each request to fast cloud storage > is > > 10KB, the size will be 100,000 times larger in KIP-1176. > > > > I'm thinking, if the WAL metadata is just for notifying followers about > > the records location in fast cloud storage, could we simplify the WAL > > metadata management by including them in the fetch response with a > special > > flag (ex: walMetadata=true) in the fetchResponse record instead? Because > > 1. When the followers successfully download the logs from the fast cloud > > storage, the metadata is useless anymore. > > 2. To help some lag behind replicas catch up, these metadata can be > stored > > in local disk under the partition folder in leader and followers nodes. > So > > when the lagged follower fetches some old data in the active log segment, > > the leader can still respond with the metadata to the follower, to let > the > > follower download the logs from fast cloud storage to avoid cross-az > cost. > > 3. If the metadata local file is not found on the leader node, we can > fall > > back to pass the pure logs directly (with cross-az cost for sure, but it > > will be rare). > > 4. The metadata local file won't be uploaded to slow cloud storage and > > will be deleted after local retention expired. > > 5. Compared with the existing design using __remote_log_metadata topic, > > the metadata is still needed to be replicated to all replicas, so the > > cross-az cost is the same. > > > > What do you think about this alternative for WAL metadata? > > > > One more question from me: > > 1. It looks like we only move "logs" to the fast cloud storage, not the > > index files, producer snapshots,...etc. Is that right? > > Because this is different from KIP-405, and it is kind of inherited from > > KIP-405, we should make it clear in the KIP. > > > > > > Thanks. > > Luke > > > > > > > > > > On Thu, May 8, 2025 at 9:54 AM Xinyu Zhou <yu...@apache.org> wrote: > > > >> Hi Henry, > >> > >> Thank you for your detailed reply. The answer makes sense to me, and > >> you're > >> right, KIP-1176 has a clear and specific scope and is expected to have a > >> quick path to implement it. > >> > >> I also want to discuss the metadata management of WAL log segments. Is > an > >> internal topic necessary for managing metadata? In AutoMQ, WAL is solely > >> for recovery and is expected to be uploaded to standard S3 as soon as > >> possible, without metadata management. I think KIP-1176 might not need > it > >> either; during recovery, we can simply scan the WAL to restore the > >> metadata. > >> > >> Regards, > >> Xinyu > >> > >> On Thu, May 8, 2025 at 2:00 AM Henry Haiying Cai > >> <haiying_...@yahoo.com.invalid> wrote: > >> > >> > Xinyu, > >> > Thanks for your time reading the KIP and detailed comments. We are > >> > honored to have technical leaders from AutoMQ to look at our work. > >> > Please see my answers below inline. > >> > > >> > On Tuesday, May 6, 2025 at 08:37:22 PM PDT, Xinyu Zhou < > >> > yu...@apache.org> wrote: > >> > > >> > Hi Henry and Tom, > >> > > >> > I've read the entire KIP-1176, and I think it's a smart move to > advance > >> > tiered storage. > >> > > >> > If I understand correctly, KIP-1176 aims to eliminate cross-AZ traffic > >> in > >> > tier 1 storage by replicating data to followers through the S3EOZ > >> bucket. > >> > After that, followers only need to replicate data from the S3EOZ > bucket, > >> > which is free for cross-AZ traffic. > >> > > >> > Based on my understanding, I have some questions: > >> > > >> > 1. Does KIP-1176 focus solely on eliminating cross-AZ traffic from > ISR > >> > replication? Have you considered using S3/S3EOZ to reduce cross-AZ > >> > traffic > >> > from the producer side as well? Actually, AutoMQ has validated and > >> > implemented this solution, you can refer to this pull request: > >> > https://github.com/AutoMQ/automq/pull/2505 > >> > HC> The focus of KIP-1176 is mainly on reducing across-AZ traffic cost > >> > between brokers which is a big percentage (like 60%) on the broker > side > >> > cost. At the moment, we are focusing only on broker side's cost and > >> > optimize producer/consumer side traffic later. I know there are > efforts > >> > from the community to optimize on AZ traffic between producer and > >> broker as > >> > well (e.g. KIP-1123), we will get benefit from across-AZ cost savings > >> from > >> > producer side when those efforts materialized. > >> > 2. KIP-1176, like AutoMQ, is a leader-based architecture that > benefits > >> > from using object storage for elastic features, such as quickly > >> > reassigning > >> > partitions. However, KIP-1176 still uses local block storage for > >> managing > >> > active log segments, so its elasticity is similar to current tiered > >> > storage, right? Will KIP-1176 consider enhancing elasticity by > >> utilizing > >> > object storage? Or is this not the scope of KIP-1176? > >> > HC> KIP-1176 is a small KIP which built on existing constructs from > >> tiered > >> > storage and also built on the existing core tenet of Kafka: page > >> cache. I > >> > know there are other efforts (e.g. KIP-1150 and AutoMQ's solution) > which > >> > proposed revamping Kafka's memory management and storage system by > >> moving > >> > everything to cloud and built memory/disk caching layers on top of > that, > >> > those are big and audacious efforts which can take years to merge back > >> into > >> > Apache Kafka. Instead we are focusing on a small and iterative > approach > >> > which can be absorbed into Apache Kafka much easier/quicker while > >> cutting a > >> > big cost portion. Although this KIP is targeting a smaller goal, but > it > >> > can also achieve a bigger goal cloud-native-elasticity if everything > is > >> > moved to cloud storage. KIP-405 moved all closed log segments to > object > >> > storage and this KIP moved active log segment to object storage, now > >> with > >> > everything on the cloud storage, the consumers now can read directly > >> from > >> > cloud storage (without connecting to the broker), in this direction > >> > majority of the traffic (consumer traffic probably comprises 2/3 of > the > >> > overall traffic) will be happening outside broker, there are much less > >> > resources we need to allocate to the broker. > >> > 3. The KIP indicates that the S3EOZ cost isn't significantly low, > with > >> > cross-AZ data transfer fees at $1612 and S3EOZ costs at $648. Many > AWS > >> > customers get substantial discounts on cross-AZ transfer fees, so the > >> > final > >> > benefit of KIP-1176 might not be significant(I am not sure). Could > you > >> > please share any updates on KIP-1176 in Slack? > >> > > >> > HC>. Yes you are right that big companies (e.g. Slack/Salesforce) get > >> > deeper discount from AWS. Since I cannot share the discount rate from > >> my > >> > company I can only quote public pricing number. But even with those > >> > discounts, across AZ traffic is still the major cost factor. > >> > Also, I’m concerned about the community. Vendors are keen to move > Kafka > >> to > >> > object storage because cloud, especially AWS, is their main market, > >> making > >> > cross-AZ traffic important. However, Apache Kafka users are spread > >> across > >> > various environments, including different cloud providers (note that > >> only > >> > AWS and GCP charge for cross-AZ traffic) and many on-premise data > >> centers. > >> > Where are most self-hosted Kafka users located? Are they deeply > >> impacted by > >> > cross-AZ traffic costs? How does the community balance these users' > >> > differing needs and weigh expected benefits against architectural > >> > complexity? > >> > > >> > HC> This KIP (KIP-1176) is mainly targeting the same set of users who > is > >> > already using KIP-405: Tiered Storage by extending support of tiered > >> > storage to active log segment. For those users, they will get extra > >> > savings on across-AZ traffic and extra benefit of having everything on > >> the > >> > cloud storage. I think in US (probably Europe as well), AWS/GCP is > the > >> > majority of the cloud market. > >> > Overall, KIP-1176 is a great idea for using S3EOZ to eliminate > cross-AZ > >> > replication traffic. Well done! > >> > > >> > Disclaimer: I work for AutoMQ, but I am wearing the community hat to > >> join > >> > this discussion thread. > >> > > >> > Regards, > >> > Xinyu > >> > > >> > On Wed, May 7, 2025 at 9:13 AM Henry Haiying Cai > >> > <haiying_...@yahoo.com.invalid> wrote: > >> > > >> > > Christo, > >> > > In terms of supporting transactional messages, I looked at the > current > >> > > FetchRequest/Response code, looks like for follower fetch it's > always > >> > > fetching to the LOG_END offset (while for consumer fetch there is a > >> > choice > >> > > of fetch up to HIGH_WATERMARK vs fetch up to TXN_COMMITTED) , since > >> our > >> > > current implementation is to copy all the way to LOG_END between > >> leader > >> > and > >> > > follower broker (through object storage), it seems it would > naturally > >> > > support replicating transactional messages as well. > >> > > On Tuesday, May 6, 2025 at 12:20:43 PM PDT, Henry Haiying Cai < > >> > > haiying_...@yahoo.com> wrote: > >> > > > >> > > Christo, > >> > > Thanks for your detailed comments and see my answer below inline. > >> > > On Tuesday, May 6, 2025 at 02:40:29 AM PDT, Christo Lolov < > >> > > christolo...@gmail.com> wrote: > >> > > > >> > > Hello! > >> > > > >> > > It is great to see another proposal on the same topic, but > optimising > >> for > >> > > different scenarios, so thanks a lot for the effort put in this! > >> > > > >> > > I have a few questions and statements in no particular order. > >> > > > >> > > If you use acks=-1 (acks=all) then an acknowledgement can only be > >> sent to > >> > > the producer if and only if the records have been persisted in > >> replicated > >> > > object storage (S3) or non-replicated object storage (S3E1AZ) and > >> > > downloaded on followers. If you do not do this, then you do not > cover > >> the > >> > > following two failure scenarios which Kafka does cover today: > >> > > > >> > > 1. Your leader persists records on disk. Your followers fetch the > >> > metadata > >> > > for these records. The high watermark on the leader advances. The > >> leader > >> > > sends acknowledgement to the producer. The records are not yet put > in > >> > > object storage. The leader crashes irrecoverably before the records > >> are > >> > > uploaded. > >> > > > >> > > 2. Your leader persists records on disk. Your followers fetch the > >> > metadata > >> > > for these records. The high watermark on the leader advances. The > >> leader > >> > > sends acknowledgement to the producer. The records are put in > >> > > non-replicated object storage, but not downloaded by followers. The > >> > > non-replicated object storage experiences prolonged unavailability. > >> The > >> > > leader crashes irrecoverably. > >> > > > >> > > In both of these scenarios you risk either data loss or data > >> > unavailability > >> > > if a single replica goes out of commission. As such, this breaks the > >> > > current definition of acks=-1 (acks=all) to the best of my > knowledge. > >> I > >> > am > >> > > happy to discuss this further if you think this is not the case. > >> > > HC > Our current implementation is to wait until the follower gets > the > >> > > producer data and FollowerState in leader's memory gets updated > >> through > >> > the > >> > > existing FollowerRequest/Response exchange (to be exact, it is the > >> > > subsequent FollowerRequest/Response after the follower has appended > >> the > >> > > producer data) before leader can acknowledge back to the producer, > >> this > >> > way > >> > > we don't have to modify the current implementation of high watermark > >> and > >> > > follower state sync. So in this implementation, there is no risks > of > >> > data > >> > > loss since follower gets the producer data as in existing code. The > >> > > drawback is the extra hop from object storage to the follower > broker, > >> it > >> > > can be mitigated by tuning download frequency. We do have a plan to > >> > > optimize the latency in acks=-1 by acks back to producer as soon as > >> the > >> > > data is uploaded onto object storage, there is code we need to add > to > >> > deal > >> > > when the old leader crashes and the new leader needs to do fast > catch > >> up > >> > > sync with object storage, we plan to propose this as an performance > >> > > optimization feature fix on top of the current proposal. On your > >> concern > >> > > of follower having the new metadata but not having the new data, the > >> > > follower gets the data from object storage download and append to > >> local > >> > log > >> > > and then update its log end offset and its offset state is then > >> > transmitted > >> > > back to the leader broker on the subsequent FetchRequest (similar to > >> how > >> > it > >> > > was doing today except the process is triggered from > >> > processFetchResponse), > >> > > the log segment metadata the follower is getting from > >> > __remote_log_metadata > >> > > topic is used to trigger the background task to download new data > >> segment > >> > > but not used to build it's local log offsets (e.g. logEndOffset), > >> local > >> > > log's offset state are built when the data is appended to the local > >> log > >> > (as > >> > > in the existing Kafka code). > >> > > > >> > > S3E1AZ only resides in 1 availability zone. This poses the following > >> > > questions: > >> > > a) Will you have 1 bucket per availability zone assuming a 3-broker > >> > cluster > >> > > where each broker is in a separate availability zone? > >> > > HC>. Yes you are right that S3E1Z is only in one AZ. So in our > >> setup, we > >> > > have the S3E1Z's bucket AZ to be the same as the leader broker's AZ, > >> and > >> > > the follower broker is from a different AZ. So the data upload from > >> > leader > >> > > broker to S3E1Z is fast (within the same AZ), the download from > object > >> > > storage to the follower is slower (across AZ), but AWS don't charge > >> extra > >> > > for that download. > >> > > b) If not, then have you ran a test on the network penalty in terms > of > >> > > latency for the 2 brokers not in the same availability zone but > being > >> > > leaders for their respective partitions? Here I am interested to see > >> what > >> > > 2/3 of any cluster will experience? > >> > > HC>. As I mentioned above, the download from the S31EZ to the > >> follower is > >> > > slower because the traffic goes across AZ, it adds about 10ms for > >> bigger > >> > > packet. And also in the situation that you mentioned that a broker > >> has > >> > > some partitions as followers but some partitions as leaders (which > is > >> > > typical in a kafka cluster), we have 3 S3E1Z buckets (one in each > AZ), > >> > when > >> > > the brokers needs to upload data onto S3E1Z for its leader > >> partitions, it > >> > > will upload to the the bucket in the same AZ as itself. The path of > >> the > >> > > file including the bucket name is part of the log segment metadata > >> > > published to the __remote_log_metadata topic, when a follower broker > >> > needs > >> > > to do the download it will use the path of the file (including the > >> bucket > >> > > name) to download, this applies to the situation to that leader > broker > >> > when > >> > > it needs to download for the partitions it act as followers. > >> > > c) On a quick search it isn't clear whether S3E1AZ incurs cross-AZ > >> > > networking data charges (again, in the case where there is only 1 > >> bucket > >> > > for the whole cluster). This might be my fault, but from the table > at > >> the > >> > > end of the KIP it isn't super obvious to me whether the transfer > cost > >> > > includes these network charges. Have you ran a test to see whether > the > >> > > pricing still makes sense? If you have could you share these numbers > >> in > >> > the > >> > > KIP? > >> > > HC> S3 (including S3E1Z) doesn't charge for across-AZ traffic (they > do > >> > > extra charge if it's across region), but the latency is longer if > the > >> > data > >> > > travels across AZ. S3E1z charges for S3 PUT (upload) and S3 GET > >> > > (download), PUT is usually 10x more expensive than GET. So we don't > >> pay > >> > > for across AZ traffic cost but we do pay for S3 PUT and GET, so the > >> batch > >> > > size and upload frequency is still important to not overrun the S3 > PUT > >> > > cost. So number still make sense if the batch size and upload > >> frequency > >> > is > >> > > set right. > >> > > > >> > > As far as I understand, this will work in conjunction with Tiered > >> Storage > >> > > as it works today. Am I correct in my reading of the KIP? If I am > >> > correct, > >> > > then how you store data in active segments seems to differ from how > TS > >> > > stores data in closed segments. In your proposal you put multiple > >> > > partitions in the same blob. What and how will move this data back > to > >> the > >> > > old format used by TS? > >> > > HC> Yes we do design to run this active log segment support along > with > >> > the > >> > > current tiered storage. And yes the data stored in the active > segment > >> > > uploaded onto S3E1Z is a bit different than the closed segment > >> uploaded > >> > > onto S3, mostly for cost reasons (as mentioned above) to combine the > >> > > content from multiple topic partitions. The upload of active log > >> > segments > >> > > onto S3E1Z and upload of closed segment onto S3 (the current tiered > >> > > storage) are running in parallel on their own. For example, assume > we > >> > set > >> > > local.retention.ms = 1-hour for a tiered-storage-enabled topic, the > >> > > proposed KIP will upload the sections of batch records from the > active > >> > log > >> > > segment onto S3E1Z when the batch records are appended into the > active > >> > log > >> > > segment on local disk. At some point this active log segment will > be > >> > > closed (when it gets to size or age threshold) and later the current > >> > tiered > >> > > storage code will upload this closed log segment onto S3 when this > >> > segment > >> > > file is more than 1 hour old. These 2 activities (uploading to > S3E1Z > >> and > >> > > uploading to S3) are independently run, there is no need to transfer > >> the > >> > > log segment file from S3E1Z to S3. There is no change to the > current > >> > code > >> > > and management of tiered storage for closed segment. > >> > > > >> > > How will you handle compaction? > >> > > HC> We currently only support the normal append-only kafka logs, > >> > compacted > >> > > kafka logs are usually not very big to benefit from this KIP > proposal. > >> > But > >> > > we can look into compacted logs later. > >> > > How will you handle indexes? > >> > > HC>. We only need to upload/download the data segment log onto > S3E1Z, > >> > > various index files are built on the follower's disk when the > follower > >> > > downloads the data and appended onto the local log on follower's > disk > >> > (just > >> > > like the existing code the indexes file are built when the data is > >> > appended > >> > > to log), there is no need to transfer the index files from leader > >> broker > >> > > onto follower broker. This is a bit different than the existing > >> tiered > >> > > storage implementation for closed log segment where you need all the > >> > states > >> > > to be stored on object storage, in our proposal the S3E1Z is just an > >> > > intermediate data hop and we are replacing the follower direct read > >> from > >> > > leader by indirect download from object storage, but we are not > >> changing > >> > > how the index file was built. > >> > > How will you handle transactions? > >> > > HC> The current implementation handles the append-only > log-end-offset > >> > > based sync between leader and follower (those logs tends to be big > and > >> > > benefit from this proposal and this is also the majority of our > >> pipelines > >> > > in our company), we plan to add the support for transactions in the > >> log > >> > > file later, there might be some extra metadata needs to be included > in > >> > > object storage, but again we are basically replacing the information > >> > > exchange in the current FetchRequest/Response. > >> > > > >> > > Once again, this is quite exciting, so thanks for the contribution! > >> > > > >> > > Best, > >> > > Christo > >> > > > >> > > On Thu, 1 May 2025 at 19:01, Henry Haiying Cai > >> > > <haiying_...@yahoo.com.invalid> wrote: > >> > > > >> > > > Luke, > >> > > > Thanks for your comments, see my answers below inline. > >> > > > On Thursday, May 1, 2025 at 03:20:54 AM PDT, Luke Chen < > >> > > > show...@gmail.com> wrote: > >> > > > > >> > > > Hi Henry, > >> > > > > >> > > > This is a very interesting proposal! > >> > > > I love the idea to minimize the code change to be able to quickly > >> get > >> > > > delivered. > >> > > > Thanks for proposing this! > >> > > > > >> > > > Some questions: > >> > > > 1. In this KIP, we add one more tier of storage. That is: local > >> disk -> > >> > > > fast object store -> slow object store. > >> > > > Why can't we allow users to replace the local disk with the fast > >> object > >> > > > store directly? Any consideration on this? > >> > > > If we don't have the local disk, the follower fetch will be much > >> > > simplified > >> > > > without downloading from the fast object store, is my > understanding > >> > > > correct? > >> > > > HC> The fast object storage is not as fast as local disk, the data > >> > > latency > >> > > > on fast object storage is going to be in 10ms for big data packets > >> and > >> > > the > >> > > > local disk append is fast since we only need to append the records > >> into > >> > > the > >> > > > page cache of the local file (the flush from page cache to disk is > >> done > >> > > > asynchronously without affecting the main request/reply cycle > >> between > >> > > > producer and leader broker). This is actually the major > difference > >> > > > between this KIP and KIP-1150, although KIP-1150 can completely > >> > removing > >> > > > the local disk but they are going to have a long latency (their > main > >> > use > >> > > > cases is for customer can tolerate 200ms latency) and they need to > >> > start > >> > > > build their own memory management and caching strategy since they > >> are > >> > not > >> > > > using page cache anymore. Our KIP has no latency change > (comparing > >> the > >> > > > current Kafka status) on acks=1 path which I believe is still the > >> > > operating > >> > > > mode for many company's logging pipelines. > >> > > > > >> > > > 2. Will the WALmetadata be deleted after the data in fast object > >> > storage > >> > > is > >> > > > deleted? > >> > > > I'm a little worried about the metadata size in the WALmetadata. I > >> > guess > >> > > > the __remote_log_metadata topic is stored in local disk only, > right? > >> > > > HC> Currently we are reusing the classes and constructs from > >> KIP-405, > >> > > e.g. > >> > > > the __remote_log_metadata topic and ConsumerManager and > >> > ProducerManager. > >> > > > As you pointed out the size of segments from active log segments > is > >> > going > >> > > > to be big, our vision is to create a separate metadata topic for > >> active > >> > > log > >> > > > segments then we can have a shorter retention setting for this > >> topic to > >> > > > remove the segment metadata faster, but we would need to refactor > >> code > >> > in > >> > > > ConsumerManager and ProducerManager to work with 2nd metadata > topic. > >> > > > > >> > > > 3. In this KIP, we assume the fast object store is different from > >> the > >> > > slow > >> > > > object store. > >> > > > Is it possible we allow users to use the same one? > >> > > > Let's say, we set both fast/slow object store = S3 (some use cases > >> > > doesn't > >> > > > care about too much on the latency), if we offload the active log > >> > segment > >> > > > onto fast object store (S3), can we not offload the segment to > slow > >> > > object > >> > > > store again after the log segment is rolled? > >> > > > I'm thinking if it's possible we learn(borrow) some ideas from > >> > KIP-1150? > >> > > > This way, we can achieve the similar goal since we accumulate > >> (combine) > >> > > > data in multiple partitions and upload to S3 to save the cost. > >> > > > > >> > > > HC> Of course people can choose just to use S3 for both fast and > >> slow > >> > > > object storage. They can have the same class implementing both > >> > > > RemoteStorageManager and RemoteWalStorageManager, we proposed > >> > > > RemoteWalStorageManager as a separate interface to give people > >> > different > >> > > > implementation choices. > >> > > > I think KIP-1176 (this one) and KIP-1150 can combine some ideas or > >> > > > implementations. We mainly focus on cutting AZ transfer cost > while > >> > > > maintaining the same performance characteristics (such as latency) > >> and > >> > > > doing a smaller evolution of the current Kafka code base. KIP-1150 > >> is a > >> > > > much ambitious effort with a complete revamp of Kafka storage and > >> > memory > >> > > > management system. > >> > > > Thank you. > >> > > > Luke > >> > > > > >> > > > On Thu, May 1, 2025 at 1:45 PM Henry Haiying Cai > >> > > > <haiying_...@yahoo.com.invalid> wrote: > >> > > > > >> > > > > Link to the KIP: > >> > > > > > >> > > > > >> > > > >> > > >> > https://cwiki.apache.org/confluence/display/KAFKA/KIP-1176%3A+Tiered+Storage+for+Active+Log+Segment > >> > > > > Motivation > >> > > > > In KIP-405, the community has proposed and implemented the > tiered > >> > > storage > >> > > > > for old Kafka log segment files, when the log segments is older > >> than > >> > > > > local.retention.ms, it becomes eligible to be uploaded to > cloud's > >> > > object > >> > > > > storage and removed from the local storage thus reducing local > >> > storage > >> > > > > cost. KIP-405 only uploads older log segments but not the most > >> > recent > >> > > > > active log segments (write-ahead logs). Thus in a typical 3-way > >> > > > replicated > >> > > > > Kafka cluster, the 2 follower brokers would still need to > >> replicate > >> > the > >> > > > > active log segments from the leader broker. It is common > practice > >> to > >> > > set > >> > > > up > >> > > > > the 3 brokers in three different AZs to improve the high > >> availability > >> > > of > >> > > > > the cluster. This would cause the replications between > >> > leader/follower > >> > > > > brokers to be across AZs which is a significant cost (various > >> studies > >> > > > show > >> > > > > the across AZ transfer cost typically comprises 50%-60% of the > >> total > >> > > > > cluster cost). Since all the active log segments are physically > >> > present > >> > > > on > >> > > > > three Kafka Brokers, they still comprise significant resource > >> usage > >> > on > >> > > > the > >> > > > > brokers. The state of the broker is still quite big during node > >> > > > > replacement, leading to longer node replacement time. KIP-1150 > >> > recently > >> > > > > proposes diskless Kafka topic, but leads to increased latency > and > >> a > >> > > > > significant redesign. In comparison, this proposed KIP maintains > >> > > > identical > >> > > > > performance for acks=1 producer path, minimizes design changes > to > >> > > Kafka, > >> > > > > and still slashes cost by an estimated 43%. > >> > > > > > >> > > > > >> > > > >> > > >> > > >
