Hi, Ying, Thanks for the update. It's good to see the progress on this. Please let us know when you are done updating the KIP wiki.
Jun On Tue, Jul 7, 2020 at 10:13 AM Ying Zheng <yi...@uber.com.invalid> wrote: > Hi Jun, > > Satish and I have added more design details in the KIP, including how to > keep consistency between replicas (especially when there is leadership > changes / log truncations) and new metrics. We also made some other minor > changes in the doc. We will finish the KIP changes in the next couple of > days. We will let you know when we are done. Most of the changes are > already updated to the wiki KIP. You can take a look. But it's not the > final version yet. > > As for the implementation, the code is mostly done and we already had some > feature tests / system tests. I have added the performance test results in > the KIP. However the recent design changes (e.g. leader epoch info > management / log truncation / some of the new metrics) have not been > implemented yet. It will take about 2 weeks for us to implement after you > review and agree with those design changes. > > > > On Tue, Jul 7, 2020 at 9:23 AM Jun Rao <j...@confluent.io> wrote: > > > Hi, Satish, Harsha, > > > > Any new updates on the KIP? This feature is one of the most important and > > most requested features in Apache Kafka right now. It would be helpful if > > we can make sustained progress on this. Could you share how far along is > > the design/implementation right now? Is there anything that other people > > can help to get it across the line? > > > > As for "transactional support" and "follower requests/replication", no > > further comments from me as long as the producer state and leader epoch > can > > be restored properly from the object store when needed. > > > > Thanks, > > > > Jun > > > > On Tue, Jun 9, 2020 at 3:39 AM Satish Duggana <satish.dugg...@gmail.com> > > wrote: > > > > > We did not want to add many implementation details in the KIP. But we > > > decided to add them in the KIP as appendix or sub-sections(including > > > follower fetch protocol) to describe the flow with the main cases. > > > That will answer most of the queries. I will update on this mail > > > thread when the respective sections are updated. > > > > > > Thanks, > > > Satish. > > > > > > On Sat, Jun 6, 2020 at 7:49 PM Alexandre Dupriez > > > <alexandre.dupr...@gmail.com> wrote: > > > > > > > > Hi Satish, > > > > > > > > A couple of questions specific to the section "Follower > > > > Requests/Replication", pages 16:17 in the design document [1]. > > > > > > > > 900. It is mentioned that followers fetch auxiliary states from the > > > > remote storage. > > > > > > > > 900.a Does the consistency model of the external storage impacts > reads > > > > of leader epochs and other auxiliary data? > > > > > > > > 900.b What are the benefits of using a mechanism to store and access > > > > the leader epochs which is different from other metadata associated > to > > > > tiered segments? What are the benefits of retrieving this information > > > > on-demand from the follower rather than relying on propagation via > the > > > > topic __remote_log_metadata? What are the advantages over using a > > > > dedicated control structure (e.g. a new record type) propagated via > > > > this topic? Since in the document, different control paths are > > > > operating in the system, how are the metadata stored in > > > > __remote_log_metadata [which also include the epoch of the leader > > > > which offloaded a segment] and the remote auxiliary states, kept in > > > > sync? > > > > > > > > 900.c A follower can encounter an OFFSET_MOVED_TO_TIERED_STORAGE. Is > > > > this in response to a Fetch or OffsetForLeaderEpoch request? > > > > > > > > 900.d What happens if, after a follower encountered an > > > > OFFSET_MOVED_TO_TIERED_STORAGE response, its attempts to retrieve > > > > leader epochs fail (for instance, because the remote storage is > > > > temporarily unavailable)? Does the follower fallbacks to a mode where > > > > it ignores tiered segments, and applies truncation using only locally > > > > available information? What happens when access to the remote storage > > > > is restored? How is the replica lineage inferred by the remote leader > > > > epochs reconciled with the follower's replica lineage, which has > > > > evolved? Does the follower remember fetching auxiliary states failed > > > > in the past and attempt reconciliation? Is there a plan to offer > > > > different strategies in this scenario, configurable via > configuration? > > > > > > > > 900.e Is the leader epoch cache offloaded with every segment? Or when > > > > a new checkpoint is detected? If that information is not always > > > > offloaded to avoid duplicating data, how does the remote storage > > > > satisfy the request to retrieve it? > > > > > > > > 900.f Since the leader epoch cache covers the entire replica lineage, > > > > what happens if, after a leader epoch cache file is offloaded with a > > > > given segment, the local epoch cache is truncated [not necessarily > for > > > > a range of offset included in tiered segments]? How are remote and > > > > local leader epoch caches kept consistent? > > > > > > > > 900.g Consumer can also use leader epochs (e.g. to enable fencing to > > > > protect against stale leaders). What differences would there be > > > > between consumer and follower fetches? Especially, would consumers > > > > also fetch leader epoch information from the remote storage? > > > > > > > > 900.h Assume a newly elected leader of a topic-partition detects more > > > > recent segments are available in the external storage, with epochs > > > > > its local epoch. Does it ignore these segments and their associated > > > > epoch-to-offset vectors? Or try to reconstruct its local replica > > > > lineage based on the data remotely available? > > > > > > > > Thanks, > > > > Alexandre > > > > > > > > [1] > > > > > > https://docs.google.com/document/d/18tnobSas3mKFZFr8oRguZoj_tkD_sGzivuLRlMloEMs/edit?usp=sharing > > > > > > > > Le jeu. 4 juin 2020 à 19:55, Satish Duggana < > satish.dugg...@gmail.com> > > > a écrit : > > > > > > > > > > Hi Jun, > > > > > Please let us know if you have any comments on "transactional > > support" > > > > > and "follower requests/replication" mentioned in the wiki. > > > > > > > > > > Thanks, > > > > > Satish. > > > > > > > > > > On Tue, Jun 2, 2020 at 9:25 PM Satish Duggana < > > > satish.dugg...@gmail.com> wrote: > > > > > > > > > > > > Thanks Jun for your comments. > > > > > > > > > > > > >100. It would be useful to provide more details on how those > apis > > > are used. Otherwise, it's kind of hard to really assess whether the new > > > apis are sufficient/redundant. A few examples below. > > > > > > > > > > > > We will update the wiki and let you know. > > > > > > > > > > > > >100.1 deleteRecords seems to only advance the logStartOffset in > > > Log. How does that trigger the deletion of remote log segments? > > > > > > > > > > > > RLMTask for leader partition periodically checks whether there > are > > > > > > remote log segments earlier to logStartOffset and the respective > > > > > > remote log segment metadata and data are deleted by using RLMM > and > > > > > > RSM. > > > > > > > > > > > > >100.2 stopReplica with deletion is used in 2 cases (a) replica > > > reassignment; (b) topic deletion. We only want to delete the tiered > > > metadata in the second case. Also, in the second case, who initiates > the > > > deletion of the remote segment since the leader may not exist? > > > > > > > > > > > > Right, it is deleted only incase of topic deletion only. We will > > > cover > > > > > > the details in the KIP. > > > > > > > > > > > > >100.3 "LogStartOffset of a topic can be either in local or in > > > remote storage." If LogStartOffset exists in both places, which one is > > the > > > source of truth? > > > > > > > > > > > > I meant the logStartOffset can point to either of local segment > or > > > > > > remote segment but it is initialised and maintained in the Log > > class > > > > > > like now. > > > > > > > > > > > > >100.4 List<RemoteLogSegmentMetadata> > > > listRemoteLogSegments(TopicPartition topicPartition, long minOffset): > How > > > is minOffset supposed to be used? > > > > > > > > > > > > Returns list of remote segments, sorted by baseOffset in > ascending > > > > > > order that have baseOffset >= the given min Offset. > > > > > > > > > > > > >100.5 When copying a segment to remote storage, it seems we are > > > calling the same RLMM.putRemoteLogSegmentData() twice before and after > > > copyLogSegment(). Could you explain why? > > > > > > > > > > > > This is more about prepare/commit/rollback as you suggested. We > > will > > > > > > update the wiki with the new APIs. > > > > > > > > > > > > >100.6 LogSegmentData includes leaderEpochCache, but there is no > > api > > > in RemoteStorageManager to retrieve it. > > > > > > > > > > > > Nice catch, copy/paste issue. There is an API to retrieve it. > > > > > > > > > > > > >101. If the __remote_log_metadata is for production usage, could > > > you provide more details? For example, what is the schema of the data > > (both > > > key and value)? How is the topic maintained,delete or compact? > > > > > > > > > > > > It is with delete config and it’s retention period is suggested > to > > be > > > > > > more than the remote retention period. > > > > > > > > > > > > >110. Is the cache implementation in RemoteLogMetadataManager > meant > > > for production usage? If so, could you provide more details on the > schema > > > and how/where the data is stored? > > > > > > > > > > > > The proposal is to have a cache (with default implementation > backed > > > by > > > > > > rocksdb) but it will be added in later versions. We will add this > > to > > > > > > future work items. > > > > > > > > > > > > >111. "Committed offsets can be stored in a local file". Could > you > > > describe the format of the file and where it's stored? > > > > > > > > > > > > We will cover this in the KIP. > > > > > > > > > > > > >112. Truncation of remote segments under unclean leader > election: > > I > > > am not sure who figures out the truncated remote segments and how that > > > information is propagated to all replicas? > > > > > > > > > > > > We will add this in detail in the KIP. > > > > > > > > > > > > >113. "If there are any failures in removing remote log segments > > > then those are stored in a specific topic (default as > > > __remote_segments_to_be_deleted)". Is it necessary to add yet another > > > internal topic? Could we just keep retrying? > > > > > > > > > > > > This is not really an internal topic, it will be exposed as a > user > > > > > > configurable topic. After a few retries, we want user to know > about > > > > > > the failure so that they can take an action later by consuming > from > > > > > > this topic. We want to keep this simple instead of retrying > > > > > > continuously and maintaining the deletion state etc. > > > > > > > > > > > > >114. "We may not need to copy producer-id-snapshot as we are > > > copying only segments earlier to last-stable-offset." Hmm, not sure > about > > > that. The producer snapshot includes things like the last timestamp of > > each > > > open producer id and can affect when those producer ids are expired. > > > > > > > > > > > > Sure, this will be added as part of the LogSegmentData. > > > > > > > > > > > > Thanks, > > > > > > Satish. > > > > > > > > > > > > > > > > > > On Fri, May 29, 2020 at 6:39 AM Jun Rao <j...@confluent.io> > wrote: > > > > > > > > > > > > > > Hi, Satish, > > > > > > > > > > > > > > Made another pass on the wiki. A few more comments below. > > > > > > > > > > > > > > 100. It would be useful to provide more details on how those > apis > > > are used. Otherwise, it's kind of hard to really assess whether the new > > > apis are sufficient/redundant. A few examples below. > > > > > > > 100.1 deleteRecords seems to only advance the logStartOffset in > > > Log. How does that trigger the deletion of remote log segments? > > > > > > > 100.2 stopReplica with deletion is used in 2 cases (a) replica > > > reassignment; (b) topic deletion. We only want to delete the tiered > > > metadata in the second case. Also, in the second case, who initiates > the > > > deletion of the remote segment since the leader may not exist? > > > > > > > 100.3 "LogStartOffset of a topic can be either in local or in > > > remote storage." If LogStartOffset exists in both places, which one is > > the > > > source of truth? > > > > > > > 100.4 List<RemoteLogSegmentMetadata> > > > listRemoteLogSegments(TopicPartition topicPartition, long minOffset): > How > > > is minOffset supposed to be used? > > > > > > > 100.5 When copying a segment to remote storage, it seems we are > > > calling the same RLMM.putRemoteLogSegmentData() twice before and after > > > copyLogSegment(). Could you explain why? > > > > > > > 100.6 LogSegmentData includes leaderEpochCache, but there is no > > > api in RemoteStorageManager to retrieve it. > > > > > > > > > > > > > > 101. If the __remote_log_metadata is for production usage, > could > > > you provide more details? For example, what is the schema of the data > > (both > > > key and value)? How is the topic maintained,delete or compact? > > > > > > > > > > > > > > 110. Is the cache implementation in RemoteLogMetadataManager > > meant > > > for production usage? If so, could you provide more details on the > schema > > > and how/where the data is stored? > > > > > > > > > > > > > > 111. "Committed offsets can be stored in a local file". Could > you > > > describe the format of the file and where it's stored? > > > > > > > > > > > > > > 112. Truncation of remote segments under unclean leader > election: > > > I am not sure who figures out the truncated remote segments and how > that > > > information is propagated to all replicas? > > > > > > > > > > > > > > 113. "If there are any failures in removing remote log segments > > > then those are stored in a specific topic (default as > > > __remote_segments_to_be_deleted)". Is it necessary to add yet another > > > internal topic? Could we just keep retrying? > > > > > > > > > > > > > > 114. "We may not need to copy producer-id-snapshot as we are > > > copying only segments earlier to last-stable-offset." Hmm, not sure > about > > > that. The producer snapshot includes things like the last timestamp of > > each > > > open producer id and can affect when those producer ids are expired. > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > Jun > > > > > > > > > > > > > > On Thu, May 28, 2020 at 5:38 AM Satish Duggana < > > > satish.dugg...@gmail.com> wrote: > > > > > > >> > > > > > > >> Hi Jun, > > > > > > >> Gentle reminder. Please go through the updated wiki and let us > > > know your comments. > > > > > > >> > > > > > > >> Thanks, > > > > > > >> Satish. > > > > > > >> > > > > > > >> On Tue, May 19, 2020 at 3:50 PM Satish Duggana < > > > satish.dugg...@gmail.com> wrote: > > > > > > >>> > > > > > > >>> Hi Jun, > > > > > > >>> Please go through the wiki which has the latest updates. > Google > > > doc is updated frequently to be in sync with wiki. > > > > > > >>> > > > > > > >>> Thanks, > > > > > > >>> Satish. > > > > > > >>> > > > > > > >>> On Tue, May 19, 2020 at 12:30 AM Jun Rao <j...@confluent.io> > > > wrote: > > > > > > >>>> > > > > > > >>>> Hi, Satish, > > > > > > >>>> > > > > > > >>>> Thanks for the update. Just to clarify. Which doc has the > > > latest updates, the wiki or the google doc? > > > > > > >>>> > > > > > > >>>> Jun > > > > > > >>>> > > > > > > >>>> On Thu, May 14, 2020 at 10:38 AM Satish Duggana < > > > satish.dugg...@gmail.com> wrote: > > > > > > >>>>> > > > > > > >>>>> Hi Jun, > > > > > > >>>>> Thanks for your comments. We updated the KIP with more > > > details. > > > > > > >>>>> > > > > > > >>>>> >100. For each of the operations related to tiering, it > would > > > be useful to provide a description on how it works with the new API. > > These > > > include things like consumer fetch, replica fetch, offsetForTimestamp, > > > retention (remote and local) by size, time and logStartOffset, topic > > > deletion, etc. This will tell us if the proposed APIs are sufficient. > > > > > > >>>>> > > > > > > >>>>> We addressed most of these APIs in the KIP. We can add more > > > details if needed. > > > > > > >>>>> > > > > > > >>>>> >101. For the default implementation based on internal > topic, > > > is it meant as a proof of concept or for production usage? I assume > that > > > it's the former. However, if it's the latter, then the KIP needs to > > > describe the design in more detail. > > > > > > >>>>> > > > > > > >>>>> It is production usage as was mentioned in an earlier mail. > > We > > > plan to update this section in the next few days. > > > > > > >>>>> > > > > > > >>>>> >102. When tiering a segment, the segment is first written > to > > > the object store and then its metadata is written to RLMM using the api > > > "void putRemoteLogSegmentData()". One potential issue with this > approach > > is > > > that if the system fails after the first operation, it leaves a garbage > > in > > > the object store that's never reclaimed. One way to improve this is to > > have > > > two separate APIs, sth like preparePutRemoteLogSegmentData() and > > > commitPutRemoteLogSegmentData(). > > > > > > >>>>> > > > > > > >>>>> That is a good point. We currently have a different way > using > > > markers in the segment but your suggestion is much better. > > > > > > >>>>> > > > > > > >>>>> >103. It seems that the transactional support and the > ability > > > to read from follower are missing. > > > > > > >>>>> > > > > > > >>>>> KIP is updated with transactional support, follower fetch > > > semantics, and reading from a follower. > > > > > > >>>>> > > > > > > >>>>> >104. It would be useful to provide a testing plan for this > > > KIP. > > > > > > >>>>> > > > > > > >>>>> We added a few tests by introducing test util for tiered > > > storage in the PR. We will provide the testing plan in the next few > days. > > > > > > >>>>> > > > > > > >>>>> Thanks, > > > > > > >>>>> Satish. > > > > > > >>>>> > > > > > > >>>>> > > > > > > >>>>> On Wed, Feb 26, 2020 at 9:43 PM Harsha Chintalapani < > > > ka...@harsha.io> wrote: > > > > > > >>>>>> > > > > > > >>>>>> > > > > > > >>>>>> > > > > > > >>>>>> > > > > > > >>>>>> > > > > > > >>>>>> On Tue, Feb 25, 2020 at 12:46 PM, Jun Rao < > j...@confluent.io > > > > > > wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Hi, Satish, > > > > > > >>>>>>> > > > > > > >>>>>>> Thanks for the updated doc. The new API seems to be an > > > improvement overall. A few more comments below. > > > > > > >>>>>>> > > > > > > >>>>>>> 100. For each of the operations related to tiering, it > > would > > > be useful to provide a description on how it works with the new API. > > These > > > include things like consumer fetch, replica fetch, offsetForTimestamp, > > > retention > > > > > > >>>>>>> (remote and local) by size, time and logStartOffset, > topic > > > deletion, etc. This will tell us if the proposed APIs are sufficient. > > > > > > >>>>>> > > > > > > >>>>>> > > > > > > >>>>>> Thanks for the feedback Jun. We will add more details > around > > > this. > > > > > > >>>>>> > > > > > > >>>>>>> > > > > > > >>>>>>> 101. For the default implementation based on internal > > topic, > > > is it meant as a proof of concept or for production usage? I assume > that > > > it's the former. However, if it's the latter, then the KIP needs to > > > describe the design in more detail. > > > > > > >>>>>> > > > > > > >>>>>> > > > > > > >>>>>> Yes it meant to be for production use. Ideally it would > be > > > good to merge this in as the default implementation for metadata > service. > > > We can add more details around design and testing. > > > > > > >>>>>> > > > > > > >>>>>>> 102. When tiering a segment, the segment is first written > > to > > > the object store and then its metadata is written to RLMM using the api > > > "void putRemoteLogSegmentData()". > > > > > > >>>>>>> One potential issue with this approach is that if the > > system > > > fails after the first operation, it leaves a garbage in the object > store > > > that's never reclaimed. One way to improve this is to have two separate > > > APIs, sth like preparePutRemoteLogSegmentData() and > > > commitPutRemoteLogSegmentData(). > > > > > > >>>>>>> > > > > > > >>>>>>> 103. It seems that the transactional support and the > > ability > > > to read from follower are missing. > > > > > > >>>>>>> > > > > > > >>>>>>> 104. It would be useful to provide a testing plan for > this > > > KIP. > > > > > > >>>>>> > > > > > > >>>>>> > > > > > > >>>>>> We are working on adding more details around transactional > > > support and coming up with test plan. > > > > > > >>>>>> Add system tests and integration tests. > > > > > > >>>>>> > > > > > > >>>>>>> Thanks, > > > > > > >>>>>>> > > > > > > >>>>>>> Jun > > > > > > >>>>>>> > > > > > > >>>>>>> On Mon, Feb 24, 2020 at 8:10 AM Satish Duggana < > > > satish.dugg...@gmail.com> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Hi Jun, > > > > > > >>>>>>> Please look at the earlier reply and let us know your > > > comments. > > > > > > >>>>>>> > > > > > > >>>>>>> Thanks, > > > > > > >>>>>>> Satish. > > > > > > >>>>>>> > > > > > > >>>>>>> On Wed, Feb 12, 2020 at 4:06 PM Satish Duggana < > > > satish.dugg...@gmail.com> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Hi Jun, > > > > > > >>>>>>> Thanks for your comments on the separation of remote log > > > metadata storage and remote log storage. > > > > > > >>>>>>> We had a few discussions since early Jan on how to > support > > > eventually consistent stores like S3 by uncoupling remote log segment > > > metadata and remote log storage. It is written with details in the doc > > > here(1). Below is the brief summary of the discussion from that doc. > > > > > > >>>>>>> > > > > > > >>>>>>> The current approach consists of pulling the remote log > > > segment metadata from remote log storage APIs. It worked fine for > > storages > > > like HDFS. But one of the problems of relying on the remote storage to > > > maintain metadata is that tiered-storage needs to be strongly > consistent, > > > with an impact not only on the metadata(e.g. LIST in S3) but also on > the > > > segment data(e.g. GET after a DELETE in S3). The cost of maintaining > > > metadata in remote storage needs to be factored in. This is true in the > > > case of S3, LIST APIs incur huge costs as you raised earlier. > > > > > > >>>>>>> So, it is good to separate the remote storage from the > > > remote log metadata store. We refactored the existing > > RemoteStorageManager > > > and introduced RemoteLogMetadataManager. Remote log metadata store > should > > > give strong consistency semantics but remote log storage can be > > eventually > > > consistent. > > > > > > >>>>>>> We can have a default implementation for > > > RemoteLogMetadataManager which uses an internal topic(as mentioned in > one > > > of our earlier emails) as storage. But users can always plugin their > own > > > RemoteLogMetadataManager implementation based on their environment. > > > > > > >>>>>>> > > > > > > >>>>>>> Please go through the updated KIP and let us know your > > > comments. We have started refactoring for the changes mentioned in the > > KIP > > > and there may be a few more updates to the APIs. > > > > > > >>>>>>> > > > > > > >>>>>>> [1] > > > > > > >>>>>>> > > > > > > >>>>>>> > > > > > > https://docs.google.com/document/d/1qfkBCWL1e7ZWkHU7brxKDBebq4ie9yK20XJnKbgAlew/edit?ts=5e208ec7# > > > > > > >>>>>>> > > > > > > >>>>>>> On Fri, Dec 27, 2019 at 5:43 PM Ivan Yurchenko < > > > ivan0yurche...@gmail.com> > > > > > > >>>>>>> > > > > > > >>>>>>> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Hi all, > > > > > > >>>>>>> > > > > > > >>>>>>> Jun: > > > > > > >>>>>>> > > > > > > >>>>>>> (a) Cost: S3 list object requests cost $0.005 per 1000 > > > requests. If > > > > > > >>>>>>> > > > > > > >>>>>>> you > > > > > > >>>>>>> > > > > > > >>>>>>> have 100,000 partitions and want to pull the metadata for > > > each > > > > > > >>>>>>> > > > > > > >>>>>>> partition > > > > > > >>>>>>> > > > > > > >>>>>>> at > > > > > > >>>>>>> > > > > > > >>>>>>> the rate of 1/sec. It can cost $0.5/sec, which is roughly > > > $40K per > > > > > > >>>>>>> > > > > > > >>>>>>> day. > > > > > > >>>>>>> > > > > > > >>>>>>> I want to note here, that no reasonably durable storage > > will > > > be cheap at 100k RPS. For example, DynamoDB might give the same > ballpark > > > > > > >>>>>>> > > > > > > >>>>>>> figures. > > > > > > >>>>>>> > > > > > > >>>>>>> If we want to keep the pull-based approach, we can try to > > > reduce this > > > > > > >>>>>>> > > > > > > >>>>>>> number > > > > > > >>>>>>> > > > > > > >>>>>>> in several ways: doing listings less frequently (as > Satish > > > mentioned, with the current defaults it's ~3.33k RPS for your example), > > > batching listing operations in some way (depending on the storage; it > > might > > > require the change of RSM's interface). > > > > > > >>>>>>> > > > > > > >>>>>>> There are different ways for doing push based metadata > > > propagation. > > > > > > >>>>>>> > > > > > > >>>>>>> Some > > > > > > >>>>>>> > > > > > > >>>>>>> object stores may support that already. For example, S3 > > > supports > > > > > > >>>>>>> > > > > > > >>>>>>> events > > > > > > >>>>>>> > > > > > > >>>>>>> notification > > > > > > >>>>>>> > > > > > > >>>>>>> This sounds interesting. However, I see a couple of > issues > > > using it: > > > > > > >>>>>>> 1. As I understand the documentation, notification > delivery > > > is not guaranteed > > > > > > >>>>>>> and it's recommended to periodically do LIST to fill the > > > gaps. Which brings us back to the same LIST consistency guarantees > issue. > > > > > > >>>>>>> 2. The same goes for the broker start: to get the current > > > state, we > > > > > > >>>>>>> > > > > > > >>>>>>> need > > > > > > >>>>>>> > > > > > > >>>>>>> to LIST. > > > > > > >>>>>>> 3. The dynamic set of multiple consumers (RSMs): AFAIK > SQS > > > and SNS > > > > > > >>>>>>> > > > > > > >>>>>>> aren't > > > > > > >>>>>>> > > > > > > >>>>>>> designed for such a case. > > > > > > >>>>>>> > > > > > > >>>>>>> Alexandre: > > > > > > >>>>>>> > > > > > > >>>>>>> A.1 As commented on PR 7561, S3 consistency model [1][2] > > > implies RSM > > > > > > >>>>>>> > > > > > > >>>>>>> cannot > > > > > > >>>>>>> > > > > > > >>>>>>> relies solely on S3 APIs to guarantee the expected strong > > > > > > >>>>>>> > > > > > > >>>>>>> consistency. The > > > > > > >>>>>>> > > > > > > >>>>>>> proposed implementation [3] would need to be updated to > > take > > > this > > > > > > >>>>>>> > > > > > > >>>>>>> into > > > > > > >>>>>>> > > > > > > >>>>>>> account. Let’s talk more about this. > > > > > > >>>>>>> > > > > > > >>>>>>> Thank you for the feedback. I clearly see the need for > > > changing the S3 implementation > > > > > > >>>>>>> to provide stronger consistency guarantees. As it see > from > > > this thread, there are > > > > > > >>>>>>> several possible approaches to this. Let's discuss > > > RemoteLogManager's contract and > > > > > > >>>>>>> behavior (like pull vs push model) further before picking > > > one (or > > > > > > >>>>>>> > > > > > > >>>>>>> several - > > > > > > >>>>>>> > > > > > > >>>>>>> ?) of them. > > > > > > >>>>>>> I'm going to do some evaluation of DynamoDB for the > > > pull-based > > > > > > >>>>>>> > > > > > > >>>>>>> approach, > > > > > > >>>>>>> > > > > > > >>>>>>> if it's possible to apply it paying a reasonable bill. > > Also, > > > of the push-based approach > > > > > > >>>>>>> with a Kafka topic as the medium. > > > > > > >>>>>>> > > > > > > >>>>>>> A.2.3 Atomicity – what does an implementation of RSM need > > to > > > provide > > > > > > >>>>>>> > > > > > > >>>>>>> with > > > > > > >>>>>>> > > > > > > >>>>>>> respect to atomicity of the APIs copyLogSegment, > > > cleanupLogUntil and deleteTopicPartition? If a partial failure happens > in > > > any of those > > > > > > >>>>>>> > > > > > > >>>>>>> (e.g. > > > > > > >>>>>>> > > > > > > >>>>>>> in > > > > > > >>>>>>> > > > > > > >>>>>>> the S3 implementation, if one of the multiple uploads > fails > > > [4]), > > > > > > >>>>>>> > > > > > > >>>>>>> The S3 implementation is going to change, but it's worth > > > clarifying > > > > > > >>>>>>> > > > > > > >>>>>>> anyway. > > > > > > >>>>>>> > > > > > > >>>>>>> The segment log file is being uploaded after S3 has acked > > > uploading of all other files associated with the segment and only after > > > this the > > > > > > >>>>>>> > > > > > > >>>>>>> whole > > > > > > >>>>>>> > > > > > > >>>>>>> segment file set becomes visible remotely for operations > > > like listRemoteSegments [1]. > > > > > > >>>>>>> In case of upload failure, the files that has been > > > successfully > > > > > > >>>>>>> > > > > > > >>>>>>> uploaded > > > > > > >>>>>>> > > > > > > >>>>>>> stays > > > > > > >>>>>>> as invisible garbage that is collected by cleanupLogUntil > > (or > > > > > > >>>>>>> > > > > > > >>>>>>> overwritten > > > > > > >>>>>>> > > > > > > >>>>>>> successfully later). > > > > > > >>>>>>> And the opposite happens during the deletion: log files > are > > > deleted > > > > > > >>>>>>> > > > > > > >>>>>>> first. > > > > > > >>>>>>> > > > > > > >>>>>>> This approach should generally work when we solve > > > consistency issues by adding a strongly consistent storage: a segment's > > > uploaded files > > > > > > >>>>>>> > > > > > > >>>>>>> remain > > > > > > >>>>>>> > > > > > > >>>>>>> invisible garbage until some metadata about them is > > written. > > > > > > >>>>>>> > > > > > > >>>>>>> A.3 Caching – storing locally the segments retrieved from > > > the remote storage is excluded as it does not align with the original > > intent > > > > > > >>>>>>> > > > > > > >>>>>>> and even > > > > > > >>>>>>> > > > > > > >>>>>>> defeat some of its purposes (save disk space etc.). That > > > said, could > > > > > > >>>>>>> > > > > > > >>>>>>> there > > > > > > >>>>>>> > > > > > > >>>>>>> be other types of use cases where the pattern of access > to > > > the > > > > > > >>>>>>> > > > > > > >>>>>>> remotely > > > > > > >>>>>>> > > > > > > >>>>>>> stored segments would benefit from local caching (and > > > potentially read-ahead)? Consider the use case of a large pool of > > consumers > > > which > > > > > > >>>>>>> > > > > > > >>>>>>> start > > > > > > >>>>>>> > > > > > > >>>>>>> a backfill at the same time for one day worth of data > from > > > one year > > > > > > >>>>>>> > > > > > > >>>>>>> ago > > > > > > >>>>>>> > > > > > > >>>>>>> stored remotely. Caching the segments locally would allow > > to > > > > > > >>>>>>> > > > > > > >>>>>>> uncouple the > > > > > > >>>>>>> > > > > > > >>>>>>> load on the remote storage from the load on the Kafka > > > cluster. Maybe > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> RLM could expose a configuration parameter to switch that > > > feature > > > > > > >>>>>>> > > > > > > >>>>>>> on/off? > > > > > > >>>>>>> > > > > > > >>>>>>> I tend to agree here, caching remote segments locally and > > > making this configurable sounds pretty practical to me. We should > > implement > > > > > > >>>>>>> > > > > > > >>>>>>> this, > > > > > > >>>>>>> > > > > > > >>>>>>> maybe not in the first iteration. > > > > > > >>>>>>> > > > > > > >>>>>>> Br, > > > > > > >>>>>>> Ivan > > > > > > >>>>>>> > > > > > > >>>>>>> [1] > > > > > > >>>>>>> > > > > > > >>>>>>> > > > > > > https://github.com/harshach/kafka/pull/18/files#diff-4d73d01c16caed6f2548fc3063550ef0R152 > > > > > > >>>>>>> > > > > > > >>>>>>> On Thu, 19 Dec 2019 at 19:49, Alexandre Dupriez < > > > > > > >>>>>>> > > > > > > >>>>>>> alexandre.dupr...@gmail.com> > > > > > > >>>>>>> > > > > > > >>>>>>> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Hi Jun, > > > > > > >>>>>>> > > > > > > >>>>>>> Thank you for the feedback. I am trying to understand > how a > > > > > > >>>>>>> > > > > > > >>>>>>> push-based > > > > > > >>>>>>> > > > > > > >>>>>>> approach would work. > > > > > > >>>>>>> In order for the metadata to be propagated (under the > > > assumption you stated), would you plan to add a new API in Kafka to > allow > > > the metadata store to send them directly to the brokers? > > > > > > >>>>>>> > > > > > > >>>>>>> Thanks, > > > > > > >>>>>>> Alexandre > > > > > > >>>>>>> > > > > > > >>>>>>> Le mer. 18 déc. 2019 à 20:14, Jun Rao <j...@confluent.io> > a > > > écrit : > > > > > > >>>>>>> > > > > > > >>>>>>> Hi, Satish and Ivan, > > > > > > >>>>>>> > > > > > > >>>>>>> There are different ways for doing push based metadata > > > > > > >>>>>>> > > > > > > >>>>>>> propagation. Some > > > > > > >>>>>>> > > > > > > >>>>>>> object stores may support that already. For example, S3 > > > supports > > > > > > >>>>>>> > > > > > > >>>>>>> events > > > > > > >>>>>>> > > > > > > >>>>>>> notification ( > > > > > > >>>>>>> > > > > > > >>>>>>> > > > https://docs.aws.amazon.com/AmazonS3/latest/dev/NotificationHowTo.html > ). > > > > > > >>>>>>> > > > > > > >>>>>>> Otherwise one could use a separate metadata store that > > > supports > > > > > > >>>>>>> > > > > > > >>>>>>> push-based > > > > > > >>>>>>> > > > > > > >>>>>>> change propagation. Other people have mentioned using a > > Kafka > > > > > > >>>>>>> > > > > > > >>>>>>> topic. The > > > > > > >>>>>>> > > > > > > >>>>>>> best approach may depend on the object store and the > > > operational environment (e.g. whether an external metadata store is > > already > > > > > > >>>>>>> > > > > > > >>>>>>> available). > > > > > > >>>>>>> > > > > > > >>>>>>> The above discussion is based on the assumption that we > > need > > > to > > > > > > >>>>>>> > > > > > > >>>>>>> cache the > > > > > > >>>>>>> > > > > > > >>>>>>> object metadata locally in every broker. I mentioned > > earlier > > > that > > > > > > >>>>>>> > > > > > > >>>>>>> an > > > > > > >>>>>>> > > > > > > >>>>>>> alternative is to just store/retrieve those metadata in > an > > > external metadata store. That may simplify the implementation in some > > cases. > > > > > > >>>>>>> > > > > > > >>>>>>> Thanks, > > > > > > >>>>>>> > > > > > > >>>>>>> Jun > > > > > > >>>>>>> > > > > > > >>>>>>> On Thu, Dec 5, 2019 at 7:01 AM Satish Duggana < > > > > > > >>>>>>> > > > > > > >>>>>>> satish.dugg...@gmail.com> > > > > > > >>>>>>> > > > > > > >>>>>>> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Hi Jun, > > > > > > >>>>>>> Thanks for your reply. > > > > > > >>>>>>> > > > > > > >>>>>>> Currently, `listRemoteSegments` is called at the > configured > > > interval(not every second, defaults to 30secs). Storing remote > > > > > > >>>>>>> > > > > > > >>>>>>> log > > > > > > >>>>>>> > > > > > > >>>>>>> metadata in a strongly consistent store for S3 RSM is > > raised > > > in PR-comment[1]. > > > > > > >>>>>>> RLM invokes RSM at regular intervals and RSM can give > > remote > > > > > > >>>>>>> > > > > > > >>>>>>> segment > > > > > > >>>>>>> > > > > > > >>>>>>> metadata if it is available. RSM is responsible for > > > maintaining > > > > > > >>>>>>> > > > > > > >>>>>>> and > > > > > > >>>>>>> > > > > > > >>>>>>> fetching those entries. It should be based on whatever > > > mechanism > > > > > > >>>>>>> > > > > > > >>>>>>> is > > > > > > >>>>>>> > > > > > > >>>>>>> consistent and efficient with the respective remote > > storage. > > > > > > >>>>>>> > > > > > > >>>>>>> Can you give more details about push based mechanism from > > > RSM? > > > > > > >>>>>>> > > > > > > >>>>>>> 1. > > > > > > >>>>>>> > > > > > > >>>>>>> > > > https://github.com/apache/kafka/pull/7561#discussion_r344576223 > > > > > > >>>>>>> > > > > > > >>>>>>> Thanks, > > > > > > >>>>>>> Satish. > > > > > > >>>>>>> > > > > > > >>>>>>> On Thu, Dec 5, 2019 at 4:23 AM Jun Rao <j...@confluent.io > > > > > wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Hi, Harsha, > > > > > > >>>>>>> > > > > > > >>>>>>> Thanks for the reply. > > > > > > >>>>>>> > > > > > > >>>>>>> 40/41. I am curious which block storages you have tested. > > S3 > > > > > > >>>>>>> > > > > > > >>>>>>> seems > > > > > > >>>>>>> > > > > > > >>>>>>> to be > > > > > > >>>>>>> > > > > > > >>>>>>> one of the popular block stores. The concerns that I have > > > with > > > > > > >>>>>>> > > > > > > >>>>>>> pull > > > > > > >>>>>>> > > > > > > >>>>>>> based > > > > > > >>>>>>> > > > > > > >>>>>>> approach are the following. > > > > > > >>>>>>> (a) Cost: S3 list object requests cost $0.005 per 1000 > > > > > > >>>>>>> > > > > > > >>>>>>> requests. If > > > > > > >>>>>>> > > > > > > >>>>>>> you > > > > > > >>>>>>> > > > > > > >>>>>>> have 100,000 partitions and want to pull the metadata for > > > each > > > > > > >>>>>>> > > > > > > >>>>>>> partition > > > > > > >>>>>>> > > > > > > >>>>>>> at > > > > > > >>>>>>> > > > > > > >>>>>>> the rate of 1/sec. It can cost $0.5/sec, which is roughly > > > $40K > > > > > > >>>>>>> > > > > > > >>>>>>> per > > > > > > >>>>>>> > > > > > > >>>>>>> day. > > > > > > >>>>>>> > > > > > > >>>>>>> (b) Semantics: S3 list objects are eventually consistent. > > So, > > > > > > >>>>>>> > > > > > > >>>>>>> when > > > > > > >>>>>>> > > > > > > >>>>>>> you > > > > > > >>>>>>> > > > > > > >>>>>>> do a > > > > > > >>>>>>> > > > > > > >>>>>>> list object request, there is no guarantee that you can > see > > > all > > > > > > >>>>>>> > > > > > > >>>>>>> uploaded > > > > > > >>>>>>> > > > > > > >>>>>>> objects. This could impact the correctness of subsequent > > > > > > >>>>>>> > > > > > > >>>>>>> logics. > > > > > > >>>>>>> > > > > > > >>>>>>> (c) Efficiency: Blindly pulling metadata when there is no > > > > > > >>>>>>> > > > > > > >>>>>>> change adds > > > > > > >>>>>>> > > > > > > >>>>>>> unnecessary overhead in the broker as well as in the > block > > > > > > >>>>>>> > > > > > > >>>>>>> store. > > > > > > >>>>>>> > > > > > > >>>>>>> So, have you guys tested S3? If so, could you share your > > > > > > >>>>>>> > > > > > > >>>>>>> experience > > > > > > >>>>>>> > > > > > > >>>>>>> in > > > > > > >>>>>>> > > > > > > >>>>>>> terms of cost, semantics and efficiency? > > > > > > >>>>>>> > > > > > > >>>>>>> Jun > > > > > > >>>>>>> > > > > > > >>>>>>> On Tue, Dec 3, 2019 at 10:11 PM Harsha Chintalapani < > > > > > > >>>>>>> > > > > > > >>>>>>> ka...@harsha.io > > > > > > >>>>>>> > > > > > > >>>>>>> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Hi Jun, > > > > > > >>>>>>> Thanks for the reply. > > > > > > >>>>>>> > > > > > > >>>>>>> On Tue, Nov 26, 2019 at 3:46 PM, Jun Rao < > j...@confluent.io > > > > > > > > > >>>>>>> > > > > > > >>>>>>> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Hi, Satish and Ying, > > > > > > >>>>>>> > > > > > > >>>>>>> Thanks for the reply. > > > > > > >>>>>>> > > > > > > >>>>>>> 40/41. There are two different ways that we can approach > > > > > > >>>>>>> > > > > > > >>>>>>> this. > > > > > > >>>>>>> > > > > > > >>>>>>> One is > > > > > > >>>>>>> > > > > > > >>>>>>> what > > > > > > >>>>>>> > > > > > > >>>>>>> you said. We can have an opinionated way of storing and > > > > > > >>>>>>> > > > > > > >>>>>>> populating > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> tier > > > > > > >>>>>>> > > > > > > >>>>>>> metadata that we think is good enough for everyone. I am > > > > > > >>>>>>> > > > > > > >>>>>>> not > > > > > > >>>>>>> > > > > > > >>>>>>> sure if > > > > > > >>>>>>> > > > > > > >>>>>>> this > > > > > > >>>>>>> > > > > > > >>>>>>> is the case based on what's currently proposed in the > KIP. > > > > > > >>>>>>> > > > > > > >>>>>>> For > > > > > > >>>>>>> > > > > > > >>>>>>> example, I > > > > > > >>>>>>> > > > > > > >>>>>>> am not sure that (1) everyone always needs local > metadata; > > > > > > >>>>>>> > > > > > > >>>>>>> (2) > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> current > > > > > > >>>>>>> > > > > > > >>>>>>> local storage format is general enough and (3) everyone > > > > > > >>>>>>> > > > > > > >>>>>>> wants to > > > > > > >>>>>>> > > > > > > >>>>>>> use > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> pull based approach to propagate the metadata. Another > > > > > > >>>>>>> > > > > > > >>>>>>> approach > > > > > > >>>>>>> > > > > > > >>>>>>> is to > > > > > > >>>>>>> > > > > > > >>>>>>> make > > > > > > >>>>>>> > > > > > > >>>>>>> this pluggable and let the implementor implements the > best > > > > > > >>>>>>> > > > > > > >>>>>>> approach > > > > > > >>>>>>> > > > > > > >>>>>>> for a > > > > > > >>>>>>> > > > > > > >>>>>>> particular block storage. I haven't seen any comments > from > > > > > > >>>>>>> > > > > > > >>>>>>> Slack/AirBnb > > > > > > >>>>>>> > > > > > > >>>>>>> in > > > > > > >>>>>>> > > > > > > >>>>>>> the mailing list on this topic. It would be great if they > > > > > > >>>>>>> > > > > > > >>>>>>> can > > > > > > >>>>>>> > > > > > > >>>>>>> provide > > > > > > >>>>>>> > > > > > > >>>>>>> feedback directly here. > > > > > > >>>>>>> > > > > > > >>>>>>> The current interfaces are designed with most popular > block > > > > > > >>>>>>> > > > > > > >>>>>>> storages > > > > > > >>>>>>> > > > > > > >>>>>>> available today and we did 2 implementations with these > > > > > > >>>>>>> > > > > > > >>>>>>> interfaces and > > > > > > >>>>>>> > > > > > > >>>>>>> they both are yielding good results as we going through > the > > > > > > >>>>>>> > > > > > > >>>>>>> testing of > > > > > > >>>>>>> > > > > > > >>>>>>> it. > > > > > > >>>>>>> > > > > > > >>>>>>> If there is ever a need for pull based approach we can > > > > > > >>>>>>> > > > > > > >>>>>>> definitely > > > > > > >>>>>>> > > > > > > >>>>>>> evolve > > > > > > >>>>>>> > > > > > > >>>>>>> the interface. > > > > > > >>>>>>> In the past we did mark interfaces to be evolving to make > > > > > > >>>>>>> > > > > > > >>>>>>> room for > > > > > > >>>>>>> > > > > > > >>>>>>> unknowns > > > > > > >>>>>>> > > > > > > >>>>>>> in the future. > > > > > > >>>>>>> If you have any suggestions around the current interfaces > > > > > > >>>>>>> > > > > > > >>>>>>> please > > > > > > >>>>>>> > > > > > > >>>>>>> propose we > > > > > > >>>>>>> > > > > > > >>>>>>> are happy to see if we can work them into it. > > > > > > >>>>>>> > > > > > > >>>>>>> 43. To offer tier storage as a general feature, ideally > all > > > > > > >>>>>>> > > > > > > >>>>>>> existing > > > > > > >>>>>>> > > > > > > >>>>>>> capabilities should still be supported. It's fine if the > > > > > > >>>>>>> > > > > > > >>>>>>> uber > > > > > > >>>>>>> > > > > > > >>>>>>> implementation doesn't support all capabilities for > > > > > > >>>>>>> > > > > > > >>>>>>> internal > > > > > > >>>>>>> > > > > > > >>>>>>> usage. > > > > > > >>>>>>> > > > > > > >>>>>>> However, the framework should be general enough. > > > > > > >>>>>>> > > > > > > >>>>>>> We agree on that as a principle. But all of these major > > > > > > >>>>>>> > > > > > > >>>>>>> features > > > > > > >>>>>>> > > > > > > >>>>>>> mostly > > > > > > >>>>>>> > > > > > > >>>>>>> coming right now and to have a new big feature such as > > tiered > > > > > > >>>>>>> > > > > > > >>>>>>> storage > > > > > > >>>>>>> > > > > > > >>>>>>> to > > > > > > >>>>>>> > > > > > > >>>>>>> support all the new features will be a big ask. We can > > > > > > >>>>>>> > > > > > > >>>>>>> document on > > > > > > >>>>>>> > > > > > > >>>>>>> how > > > > > > >>>>>>> > > > > > > >>>>>>> do > > > > > > >>>>>>> > > > > > > >>>>>>> we approach solving these in future iterations. > > > > > > >>>>>>> Our goal is to make this tiered storage feature work for > > > > > > >>>>>>> > > > > > > >>>>>>> everyone. > > > > > > >>>>>>> > > > > > > >>>>>>> 43.3 This is more than just serving the tier-ed data from > > > > > > >>>>>>> > > > > > > >>>>>>> block > > > > > > >>>>>>> > > > > > > >>>>>>> storage. > > > > > > >>>>>>> > > > > > > >>>>>>> With KIP-392, the consumer now can resolve the conflicts > > > > > > >>>>>>> > > > > > > >>>>>>> with the > > > > > > >>>>>>> > > > > > > >>>>>>> replica > > > > > > >>>>>>> > > > > > > >>>>>>> based on leader epoch. So, we need to make sure that > > > > > > >>>>>>> > > > > > > >>>>>>> leader epoch > > > > > > >>>>>>> > > > > > > >>>>>>> can be > > > > > > >>>>>>> > > > > > > >>>>>>> recovered properly from tier storage. > > > > > > >>>>>>> > > > > > > >>>>>>> We are working on testing our approach and we will update > > > > > > >>>>>>> > > > > > > >>>>>>> the KIP > > > > > > >>>>>>> > > > > > > >>>>>>> with > > > > > > >>>>>>> > > > > > > >>>>>>> design details. > > > > > > >>>>>>> > > > > > > >>>>>>> 43.4 For JBOD, if tier storage stores the tier metadata > > > > > > >>>>>>> > > > > > > >>>>>>> locally, we > > > > > > >>>>>>> > > > > > > >>>>>>> need to > > > > > > >>>>>>> > > > > > > >>>>>>> support moving such metadata across disk directories > since > > > > > > >>>>>>> > > > > > > >>>>>>> JBOD > > > > > > >>>>>>> > > > > > > >>>>>>> supports > > > > > > >>>>>>> > > > > > > >>>>>>> moving data across disks. > > > > > > >>>>>>> > > > > > > >>>>>>> KIP is updated with JBOD details. Having said that JBOD > > > > > > >>>>>>> > > > > > > >>>>>>> tooling > > > > > > >>>>>>> > > > > > > >>>>>>> needs > > > > > > >>>>>>> > > > > > > >>>>>>> to > > > > > > >>>>>>> > > > > > > >>>>>>> evolve to support production loads. Most of the users > will > > be > > > > > > >>>>>>> > > > > > > >>>>>>> interested in > > > > > > >>>>>>> > > > > > > >>>>>>> using tiered storage without JBOD support support on day > 1. > > > > > > >>>>>>> > > > > > > >>>>>>> Thanks, > > > > > > >>>>>>> Harsha > > > > > > >>>>>>> > > > > > > >>>>>>> As for meeting, we could have a KIP e-meeting on this if > > > > > > >>>>>>> > > > > > > >>>>>>> needed, > > > > > > >>>>>>> > > > > > > >>>>>>> but it > > > > > > >>>>>>> > > > > > > >>>>>>> will be open to everyone and will be recorded and shared. > > > > > > >>>>>>> > > > > > > >>>>>>> Often, > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> details are still resolved through the mailing list. > > > > > > >>>>>>> > > > > > > >>>>>>> Jun > > > > > > >>>>>>> > > > > > > >>>>>>> On Tue, Nov 19, 2019 at 6:48 PM Ying Zheng > > > > > > >>>>>>> > > > > > > >>>>>>> <yi...@uber.com.invalid> > > > > > > >>>>>>> > > > > > > >>>>>>> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Please ignore my previous email > > > > > > >>>>>>> I didn't know Apache requires all the discussions to be > > > > > > >>>>>>> > > > > > > >>>>>>> "open" > > > > > > >>>>>>> > > > > > > >>>>>>> On Tue, Nov 19, 2019, 5:40 PM Ying Zheng <yi...@uber.com > > > > > > > > >>>>>>> > > > > > > >>>>>>> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Hi Jun, > > > > > > >>>>>>> > > > > > > >>>>>>> Thank you very much for your feedback! > > > > > > >>>>>>> > > > > > > >>>>>>> Can we schedule a meeting in your Palo Alto office in > > > > > > >>>>>>> > > > > > > >>>>>>> December? I > > > > > > >>>>>>> > > > > > > >>>>>>> think a > > > > > > >>>>>>> > > > > > > >>>>>>> face to face discussion is much more efficient than > > > > > > >>>>>>> > > > > > > >>>>>>> emails. Both > > > > > > >>>>>>> > > > > > > >>>>>>> Harsha > > > > > > >>>>>>> > > > > > > >>>>>>> and > > > > > > >>>>>>> > > > > > > >>>>>>> I can visit you. Satish may be able to join us remotely. > > > > > > >>>>>>> > > > > > > >>>>>>> On Fri, Nov 15, 2019 at 11:04 AM Jun Rao < > j...@confluent.io > > > > > > >>>>>>> > > > > > > >>>>>>> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Hi, Satish and Harsha, > > > > > > >>>>>>> > > > > > > >>>>>>> The following is a more detailed high level feedback for > > > > > > >>>>>>> > > > > > > >>>>>>> the KIP. > > > > > > >>>>>>> > > > > > > >>>>>>> Overall, > > > > > > >>>>>>> > > > > > > >>>>>>> the KIP seems useful. The challenge is how to design it > > > > > > >>>>>>> > > > > > > >>>>>>> such that > > > > > > >>>>>>> > > > > > > >>>>>>> it’s > > > > > > >>>>>>> > > > > > > >>>>>>> general enough to support different ways of implementing > > > > > > >>>>>>> > > > > > > >>>>>>> this > > > > > > >>>>>>> > > > > > > >>>>>>> feature > > > > > > >>>>>>> > > > > > > >>>>>>> and > > > > > > >>>>>>> > > > > > > >>>>>>> support existing features. > > > > > > >>>>>>> > > > > > > >>>>>>> 40. Local segment metadata storage: The KIP makes the > > > > > > >>>>>>> > > > > > > >>>>>>> assumption > > > > > > >>>>>>> > > > > > > >>>>>>> that > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> metadata for the archived log segments are cached locally > > > > > > >>>>>>> > > > > > > >>>>>>> in > > > > > > >>>>>>> > > > > > > >>>>>>> every > > > > > > >>>>>>> > > > > > > >>>>>>> broker > > > > > > >>>>>>> > > > > > > >>>>>>> and provides a specific implementation for the local > > > > > > >>>>>>> > > > > > > >>>>>>> storage in > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> framework. We probably should discuss this more. For > > > > > > >>>>>>> > > > > > > >>>>>>> example, > > > > > > >>>>>>> > > > > > > >>>>>>> some > > > > > > >>>>>>> > > > > > > >>>>>>> tier > > > > > > >>>>>>> > > > > > > >>>>>>> storage providers may not want to cache the metadata > > > > > > >>>>>>> > > > > > > >>>>>>> locally and > > > > > > >>>>>>> > > > > > > >>>>>>> just > > > > > > >>>>>>> > > > > > > >>>>>>> rely > > > > > > >>>>>>> > > > > > > >>>>>>> upon a remote key/value store if such a store is already > > > > > > >>>>>>> > > > > > > >>>>>>> present. If > > > > > > >>>>>>> > > > > > > >>>>>>> a > > > > > > >>>>>>> > > > > > > >>>>>>> local store is used, there could be different ways of > > > > > > >>>>>>> > > > > > > >>>>>>> implementing it > > > > > > >>>>>>> > > > > > > >>>>>>> (e.g., based on customized local files, an embedded local > > > > > > >>>>>>> > > > > > > >>>>>>> store > > > > > > >>>>>>> > > > > > > >>>>>>> like > > > > > > >>>>>>> > > > > > > >>>>>>> RocksDB, etc). An alternative of designing this is to > just > > > > > > >>>>>>> > > > > > > >>>>>>> provide an > > > > > > >>>>>>> > > > > > > >>>>>>> interface for retrieving the tier segment metadata and > > > > > > >>>>>>> > > > > > > >>>>>>> leave the > > > > > > >>>>>>> > > > > > > >>>>>>> details > > > > > > >>>>>>> > > > > > > >>>>>>> of > > > > > > >>>>>>> > > > > > > >>>>>>> how to get the metadata outside of the framework. > > > > > > >>>>>>> > > > > > > >>>>>>> 41. RemoteStorageManager interface and the usage of the > > > > > > >>>>>>> > > > > > > >>>>>>> interface in > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> framework: I am not sure if the interface is general > > > > > > >>>>>>> > > > > > > >>>>>>> enough. For > > > > > > >>>>>>> > > > > > > >>>>>>> example, > > > > > > >>>>>>> > > > > > > >>>>>>> it seems that RemoteLogIndexEntry is tied to a specific > > > > > > >>>>>>> > > > > > > >>>>>>> way of > > > > > > >>>>>>> > > > > > > >>>>>>> storing > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> metadata in remote storage. The framework uses > > > > > > >>>>>>> > > > > > > >>>>>>> listRemoteSegments() > > > > > > >>>>>>> > > > > > > >>>>>>> api > > > > > > >>>>>>> > > > > > > >>>>>>> in > > > > > > >>>>>>> > > > > > > >>>>>>> a pull based approach. However, in some other > > > > > > >>>>>>> > > > > > > >>>>>>> implementations, a > > > > > > >>>>>>> > > > > > > >>>>>>> push > > > > > > >>>>>>> > > > > > > >>>>>>> based > > > > > > >>>>>>> approach may be more preferred. I don’t have a concrete > > > > > > >>>>>>> > > > > > > >>>>>>> proposal > > > > > > >>>>>>> > > > > > > >>>>>>> yet. > > > > > > >>>>>>> > > > > > > >>>>>>> But, > > > > > > >>>>>>> > > > > > > >>>>>>> it would be useful to give this area some more thoughts > > > > > > >>>>>>> > > > > > > >>>>>>> and see > > > > > > >>>>>>> > > > > > > >>>>>>> if we > > > > > > >>>>>>> > > > > > > >>>>>>> can > > > > > > >>>>>>> > > > > > > >>>>>>> make the interface more general. > > > > > > >>>>>>> > > > > > > >>>>>>> 42. In the diagram, the RemoteLogManager is side by side > > > > > > >>>>>>> > > > > > > >>>>>>> with > > > > > > >>>>>>> > > > > > > >>>>>>> LogManager. > > > > > > >>>>>>> > > > > > > >>>>>>> This KIP only discussed how the fetch request is handled > > > > > > >>>>>>> > > > > > > >>>>>>> between > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> two > > > > > > >>>>>>> > > > > > > >>>>>>> layer. However, we should also consider how other > requests > > > > > > >>>>>>> > > > > > > >>>>>>> that > > > > > > >>>>>>> > > > > > > >>>>>>> touch > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> log can be handled. e.g., list offsets by timestamp, > delete > > > > > > >>>>>>> > > > > > > >>>>>>> records, > > > > > > >>>>>>> > > > > > > >>>>>>> etc. > > > > > > >>>>>>> > > > > > > >>>>>>> Also, in this model, it's not clear which component is > > > > > > >>>>>>> > > > > > > >>>>>>> responsible > > > > > > >>>>>>> > > > > > > >>>>>>> for > > > > > > >>>>>>> > > > > > > >>>>>>> managing the log start offset. It seems that the log > start > > > > > > >>>>>>> > > > > > > >>>>>>> offset > > > > > > >>>>>>> > > > > > > >>>>>>> could > > > > > > >>>>>>> > > > > > > >>>>>>> be > > > > > > >>>>>>> > > > > > > >>>>>>> changed by both RemoteLogManager and LogManager. > > > > > > >>>>>>> > > > > > > >>>>>>> 43. There are quite a few existing features not covered > by > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> KIP. > > > > > > >>>>>>> > > > > > > >>>>>>> It > > > > > > >>>>>>> > > > > > > >>>>>>> would be useful to discuss each of those. > > > > > > >>>>>>> 43.1 I won’t say that compacted topics are rarely used > and > > > > > > >>>>>>> > > > > > > >>>>>>> always > > > > > > >>>>>>> > > > > > > >>>>>>> small. > > > > > > >>>>>>> > > > > > > >>>>>>> For example, KStreams uses compacted topics for storing > the > > > > > > >>>>>>> > > > > > > >>>>>>> states > > > > > > >>>>>>> > > > > > > >>>>>>> and > > > > > > >>>>>>> > > > > > > >>>>>>> sometimes the size of the topic could be large. While it > > > > > > >>>>>>> > > > > > > >>>>>>> might > > > > > > >>>>>>> > > > > > > >>>>>>> be ok > > > > > > >>>>>>> > > > > > > >>>>>>> to > > > > > > >>>>>>> > > > > > > >>>>>>> not > > > > > > >>>>>>> > > > > > > >>>>>>> support compacted topics initially, it would be useful to > > > > > > >>>>>>> > > > > > > >>>>>>> have a > > > > > > >>>>>>> > > > > > > >>>>>>> high > > > > > > >>>>>>> > > > > > > >>>>>>> level > > > > > > >>>>>>> idea on how this might be supported down the road so that > > > > > > >>>>>>> > > > > > > >>>>>>> we > > > > > > >>>>>>> > > > > > > >>>>>>> don’t > > > > > > >>>>>>> > > > > > > >>>>>>> have > > > > > > >>>>>>> > > > > > > >>>>>>> to > > > > > > >>>>>>> > > > > > > >>>>>>> make incompatible API changes in the future. > > > > > > >>>>>>> 43.2 We need to discuss how EOS is supported. In > > > > > > >>>>>>> > > > > > > >>>>>>> particular, how > > > > > > >>>>>>> > > > > > > >>>>>>> is > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> producer state integrated with the remote storage. 43.3 > > > > > > >>>>>>> > > > > > > >>>>>>> Now that > > > > > > >>>>>>> > > > > > > >>>>>>> KIP-392 > > > > > > >>>>>>> > > > > > > >>>>>>> (allow consumers to fetch from closest replica) is > > > > > > >>>>>>> > > > > > > >>>>>>> implemented, > > > > > > >>>>>>> > > > > > > >>>>>>> we > > > > > > >>>>>>> > > > > > > >>>>>>> need > > > > > > >>>>>>> > > > > > > >>>>>>> to > > > > > > >>>>>>> > > > > > > >>>>>>> discuss how reading from a follower replica is supported > > > > > > >>>>>>> > > > > > > >>>>>>> with > > > > > > >>>>>>> > > > > > > >>>>>>> tier > > > > > > >>>>>>> > > > > > > >>>>>>> storage. > > > > > > >>>>>>> > > > > > > >>>>>>> 43.4 We need to discuss how JBOD is supported with tier > > > > > > >>>>>>> > > > > > > >>>>>>> storage. > > > > > > >>>>>>> > > > > > > >>>>>>> Thanks, > > > > > > >>>>>>> > > > > > > >>>>>>> Jun > > > > > > >>>>>>> > > > > > > >>>>>>> On Fri, Nov 8, 2019 at 12:06 AM Tom Bentley < > > > > > > >>>>>>> > > > > > > >>>>>>> tbent...@redhat.com > > > > > > >>>>>>> > > > > > > >>>>>>> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Thanks for those insights Ying. > > > > > > >>>>>>> > > > > > > >>>>>>> On Thu, Nov 7, 2019 at 9:26 PM Ying Zheng > > > > > > >>>>>>> > > > > > > >>>>>>> <yi...@uber.com.invalid > > > > > > >>>>>>> > > > > > > >>>>>>> wrote: > > > > > > >>>>>>> > > > > > > >>>>>>> Thanks, I missed that point. However, there's still a > > > > > > >>>>>>> > > > > > > >>>>>>> point at > > > > > > >>>>>>> > > > > > > >>>>>>> which > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> consumer fetches start getting served from remote storage > > > > > > >>>>>>> > > > > > > >>>>>>> (even > > > > > > >>>>>>> > > > > > > >>>>>>> if > > > > > > >>>>>>> > > > > > > >>>>>>> that > > > > > > >>>>>>> > > > > > > >>>>>>> point isn't as soon as the local log retention > time/size). > > > > > > >>>>>>> > > > > > > >>>>>>> This > > > > > > >>>>>>> > > > > > > >>>>>>> represents > > > > > > >>>>>>> > > > > > > >>>>>>> a kind of performance cliff edge and what I'm really > > > > > > >>>>>>> > > > > > > >>>>>>> interested > > > > > > >>>>>>> > > > > > > >>>>>>> in > > > > > > >>>>>>> > > > > > > >>>>>>> is > > > > > > >>>>>>> > > > > > > >>>>>>> how > > > > > > >>>>>>> > > > > > > >>>>>>> easy it is for a consumer which falls off that cliff to > > > > > > >>>>>>> > > > > > > >>>>>>> catch up > > > > > > >>>>>>> > > > > > > >>>>>>> and so > > > > > > >>>>>>> > > > > > > >>>>>>> its > > > > > > >>>>>>> > > > > > > >>>>>>> fetches again come from local storage. Obviously this can > > > > > > >>>>>>> > > > > > > >>>>>>> depend > > > > > > >>>>>>> > > > > > > >>>>>>> on > > > > > > >>>>>>> > > > > > > >>>>>>> all > > > > > > >>>>>>> > > > > > > >>>>>>> sorts of factors (like production rate, consumption > rate), > > > > > > >>>>>>> > > > > > > >>>>>>> so > > > > > > >>>>>>> > > > > > > >>>>>>> it's > > > > > > >>>>>>> > > > > > > >>>>>>> not > > > > > > >>>>>>> > > > > > > >>>>>>> guaranteed (just like it's not guaranteed for Kafka > > > > > > >>>>>>> > > > > > > >>>>>>> today), but > > > > > > >>>>>>> > > > > > > >>>>>>> this > > > > > > >>>>>>> > > > > > > >>>>>>> would > > > > > > >>>>>>> > > > > > > >>>>>>> represent a new failure mode. > > > > > > >>>>>>> > > > > > > >>>>>>> As I have explained in the last mail, it's a very rare > > > > > > >>>>>>> > > > > > > >>>>>>> case that > > > > > > >>>>>>> > > > > > > >>>>>>> a > > > > > > >>>>>>> > > > > > > >>>>>>> consumer > > > > > > >>>>>>> need to read remote data. With our experience at Uber, > > > > > > >>>>>>> > > > > > > >>>>>>> this only > > > > > > >>>>>>> > > > > > > >>>>>>> happens > > > > > > >>>>>>> > > > > > > >>>>>>> when the consumer service had an outage for several > hours. > > > > > > >>>>>>> > > > > > > >>>>>>> There is not a "performance cliff" as you assume. The > > > > > > >>>>>>> > > > > > > >>>>>>> remote > > > > > > >>>>>>> > > > > > > >>>>>>> storage > > > > > > >>>>>>> > > > > > > >>>>>>> is > > > > > > >>>>>>> > > > > > > >>>>>>> even faster than local disks in terms of bandwidth. > > > > > > >>>>>>> > > > > > > >>>>>>> Reading from > > > > > > >>>>>>> > > > > > > >>>>>>> remote > > > > > > >>>>>>> > > > > > > >>>>>>> storage is going to have higher latency than local disk. > > > > > > >>>>>>> > > > > > > >>>>>>> But > > > > > > >>>>>>> > > > > > > >>>>>>> since > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> consumer > > > > > > >>>>>>> is catching up several hours data, it's not sensitive to > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> sub-second > > > > > > >>>>>>> > > > > > > >>>>>>> level > > > > > > >>>>>>> latency, and each remote read request will read a large > > > > > > >>>>>>> > > > > > > >>>>>>> amount of > > > > > > >>>>>>> > > > > > > >>>>>>> data to > > > > > > >>>>>>> > > > > > > >>>>>>> make the overall performance better than reading from > local > > > > > > >>>>>>> > > > > > > >>>>>>> disks. > > > > > > >>>>>>> > > > > > > >>>>>>> Another aspect I'd like to understand better is the > effect > > > > > > >>>>>>> > > > > > > >>>>>>> of > > > > > > >>>>>>> > > > > > > >>>>>>> serving > > > > > > >>>>>>> > > > > > > >>>>>>> fetch > > > > > > >>>>>>> > > > > > > >>>>>>> request from remote storage has on the broker's network > > > > > > >>>>>>> > > > > > > >>>>>>> utilization. If > > > > > > >>>>>>> > > > > > > >>>>>>> we're just trimming the amount of data held locally > > > > > > >>>>>>> > > > > > > >>>>>>> (without > > > > > > >>>>>>> > > > > > > >>>>>>> increasing > > > > > > >>>>>>> > > > > > > >>>>>>> the > > > > > > >>>>>>> > > > > > > >>>>>>> overall local+remote retention), then we're effectively > > > > > > >>>>>>> > > > > > > >>>>>>> trading > > > > > > >>>>>>> > > > > > > >>>>>>> disk > > > > > > >>>>>>> > > > > > > >>>>>>> bandwidth for network bandwidth when serving fetch > > > > > > >>>>>>> > > > > > > >>>>>>> requests from > > > > > > >>>>>>> > > > > > > >>>>>>> remote > > > > > > >>>>>>> > > > > > > >>>>>>> storage (which I understand to be a good thing, since > > > > > > >>>>>>> > > > > > > >>>>>>> brokers are > > > > > > >>>>>>> > > > > > > >>>>>>> often/usually disk bound). But if we're increasing the > > > > > > >>>>>>> > > > > > > >>>>>>> overall > > > > > > >>>>>>> > > > > > > >>>>>>> local+remote > > > > > > >>>>>>> > > > > > > >>>>>>> retention then it's more likely that network itself > > > > > > >>>>>>> > > > > > > >>>>>>> becomes the > > > > > > >>>>>>> > > > > > > >>>>>>> bottleneck. > > > > > > >>>>>>> > > > > > > >>>>>>> I appreciate this is all rather hand wavy, I'm just > trying > > > > > > >>>>>>> > > > > > > >>>>>>> to > > > > > > >>>>>>> > > > > > > >>>>>>> understand > > > > > > >>>>>>> > > > > > > >>>>>>> how this would affect broker performance, so I'd be > > > > > > >>>>>>> > > > > > > >>>>>>> grateful for > > > > > > >>>>>>> > > > > > > >>>>>>> any > > > > > > >>>>>>> > > > > > > >>>>>>> insights you can offer. > > > > > > >>>>>>> > > > > > > >>>>>>> Network bandwidth is a function of produce speed, it has > > > > > > >>>>>>> > > > > > > >>>>>>> nothing > > > > > > >>>>>>> > > > > > > >>>>>>> to > > > > > > >>>>>>> > > > > > > >>>>>>> do > > > > > > >>>>>>> > > > > > > >>>>>>> with > > > > > > >>>>>>> > > > > > > >>>>>>> remote retention. As long as the data is shipped to > remote > > > > > > >>>>>>> > > > > > > >>>>>>> storage, > > > > > > >>>>>>> > > > > > > >>>>>>> you > > > > > > >>>>>>> > > > > > > >>>>>>> can > > > > > > >>>>>>> > > > > > > >>>>>>> keep the data there for 1 day or 1 year or 100 years, it > > > > > > >>>>>>> > > > > > > >>>>>>> doesn't > > > > > > >>>>>>> > > > > > > >>>>>>> consume > > > > > > >>>>>>> > > > > > > >>>>>>> any > > > > > > >>>>>>> network resources. > > > > > > >>>>>> > > > > > > >>>>>> > > > > > >
