HI Jun, Thanks for your comments. We put our inline replies below. 1001. I was thinking that you could just use the tiered metadata to do the reconciliation. The tiered metadata contains offset ranges and epoch history. Those should be enough for reconciliation purposes.
If we use remote storage as the source-of-truth during unclean-leader-election, it's possible that after reconciliation the remote storage will have more recent data than the new leader's local storage. For example, the new leader's latest message is offset 1000, while the remote storage has message 1100. In such a case, the new leader will have to download the messages from 1001 to 1100, before accepting new messages from producers. Otherwise, there would be a gap in the local data between 1000 and 1101. Moreover, with the current design, leader epoch history is stored in remote storage, rather than the metadata topic. We did consider saving epoch history in remote segment metadata. But the concern is that there is currently no limit for the epoch history size. Theoretically, if a user has a very long remote retention time and there are very frequent leadership changes, the leader epoch history can become too long to fit into a regular Kafka message. 1003.3 Having just a serverEndpoint string is probably not enough. Connecting to a Kafka cluster may need various security credentials. We can make RLMM configurable and pass in the properties through the configure() method. Ditto for RSM. RLMM and RSM are already configurable and they take properties which start with "remote.log.metadata." and "remote.log.storage." respectively and a few others. We have listener-name as the config for RLMM and other properties(like security) can be sent as you suggested. We will update the KIP with the details. 1008.1 We started with log.retention.hours and log.retention.minutes, and added log.retention.ms later. If we are adding a new configuration, ms level config alone is enough and is simpler. We can build tools to make the configuration at different granularities easier. The definition of log.retention.ms is "The number of milliseconds to keep a log file before deleting it". The deletion is independent of whether tiering is enabled or not. If this changes to just the local portion of the data, we are changing the meaning of an existing configuration. We are fine with either way. We can go with log.retention.xxxx as the effective log retention instead of local log retention. With this convention, we need to introduce local.log.retention instead of remote.log.retention.ms that we proposed. If log.retention.ms as -1 then remote retention is also considered as unlimited but user should be able to set the local.retention.ms. So, we need to introduce local.log.retention.ms and local.log.retention.bytes which should always be <= log.retention.ms/bytes respectively. On Fri, Jul 24, 2020 at 3:37 AM Jun Rao <j...@confluent.io> wrote: > > Hi, Satish, > > Thanks for the reply. A few quick comments below. > > 1001. I was thinking that you could just use the tiered metadata to do the > reconciliation. The tiered metadata contains offset ranges and epoch > history. Those should be enough for reconciliation purposes. > > 1003.3 Having just a serverEndpoint string is probably not enough. > Connecting to a Kafka cluster may need various security credentials. We can > make RLMM configurable and pass in the properties through the configure() > method. Ditto for RSM. > > 1008.1 We started with log.retention.hours and log.retention.minutes, and > added log.retention.ms later. If we are adding a new configuration, ms > level config alone is enough and is simpler. We can build tools to make the > configuration at different granularities easier. The definition of > log.retention.ms is "The number of milliseconds to keep a log file before > deleting it". The deletion is independent of whether tiering is enabled or > not. If this changes to just the local portion of the data, we are changing > the meaning of an existing configuration. > > Jun > > > On Thu, Jul 23, 2020 at 11:04 AM Satish Duggana <satish.dugg...@gmail.com> > wrote: > > > Hi Jun, > > > > Thank you for the comments! Ying, Harsha and I discussed and put our > > comments below. > > > > > > 1001. The KIP described a few scenarios of unclean leader elections. This > > is very useful, but I am wondering if this is the best approach. My > > understanding of the proposed approach is to allow the new (unclean) leader > > to take new messages immediately. While this increases availability, it > > creates the problem that there could be multiple conflicting segments in > > the remote store for the same offset range. This seems to make it harder > > for RLMM to determine which archived log segments contain the correct data. > > For example, an archived log segment could at one time be the correct data, > > but be changed to incorrect data after an unclean leader election. An > > alternative approach is to let the unclean leader use the archived data as > > the source of truth. So, when the new (unclean) leader takes over, it first > > reconciles the local data based on the archived data before taking new > > messages. This makes the job of RLMM a bit easier since all archived data > > are considered correct. This increases availability a bit. However, since > > unclean leader elections are rare, this may be ok. > > > > Firstly, We don't want to assume the remote storage is more reliable than > > Kafka. Kafka unclean leader election usually happens when there is a large > > scale outage that impacts multiple racks (or even multiple availability > > zones). In such a case, the remote storage may be unavailable or unstable. > > Pulling a large amount of data from the remote storage to reconcile the > > local data may also exacerbate the outage. With the current design, the new > > leader can start working even when the remote storage is temporarily > > unavailable. > > > > Secondly, it is not easier to implement the reconciling logic at the leader > > side. It can take a long time for the new leader to download the remote > > data and rebuild local producer id / leader epoch information. During this > > period, the leader cannot accept any requests from the clients and > > followers. We have to introduce a new state for the leader, and a new error > > code to let the clients / followers know what is happening. > > > > > > > > 1002. RemoteStorageManager. > > 1002.1 There seems to be some inconsistencies in RemoteStorageManager. We > > pass in RemoteLogSegmentId copyLogSegment(). For all other methods, we pass > > in RemoteLogSegmentMetadata. > > > > Nice catch, we can have the RemoteLogSegmentMetadata for copyLogSegment > > too. > > > > 1002.2 Is endOffset in RemoteLogSegmentMetadata inclusive or exclusive? > > > > It is inclusive. > > > > 1002.3 It seems that we need an api to get the leaderEpoch history for a > > partition. > > > > Yes, updated the KIP with the new method. > > > > > > 1002.4 Could you define the type of RemoteLogSegmentContext? > > > > This is removed in the latest code and it is not needed. > > > > > > 1003 RemoteLogMetadataManager > > > > 1003.1 I am not sure why we need both of the following methods > > in RemoteLogMetadataManager. Could we combine them into one that takes in > > offset and returns RemoteLogSegmentMetadata? > > RemoteLogSegmentId getRemoteLogSegmentId(TopicPartition topicPartition, > > long offset) throws IOException; > > RemoteLogSegmentMetadata getRemoteLogSegmentMetadata(RemoteLogSegmentId > > remoteLogSegmentId) throws IOException; > > > > Good point, these can be merged for now. I guess we needed them in earlier > > version of the implementation but it is not needed now. > > > > 1003.2 There seems to be some inconsistencies in the methods below. I am > > not sure why one takes RemoteLogSegmentMetadata and the other > > takes RemoteLogSegmentId. > > void putRemoteLogSegmentData(RemoteLogSegmentMetadata > > remoteLogSegmentMetadata) throws IOException; > > void deleteRemoteLogSegmentMetadata(RemoteLogSegmentId > > remoteLogSegmentId) throws IOException; > > > > RLMM stores RemoteLogSegmentMetadata which is identified by > > RemoteLogsSegmentId. So, when it is added it takes > > RemoteLogSegmentMetadata. `delete` operation needs only RemoteLogsSegmentId > > as RemoteLogSegmentMetadata can be identified with RemoteLogsSegmentId. > > > > 1003.3 In void onServerStarted(final String serverEndpoint), what > > is serverEndpoint used for? > > > > This can be used by RLMM implementation to connect to the local Kafka > > cluster. Incase of default implementation, it is used in initializing > > kafka clients connecting to the local cluster. > > > > 1004. It would be useful to document how all the new APIs are being used. > > For example, when is RemoteLogSegmentMetadata.markedForDeletion being set > > and used? How are > > RemoteLogMetadataManager.earliestLogOffset/highestLogOffset being used? > > > > RLMM APIs are going through the changes and they should be ready in a few > > days. I will update the KIP and the mail thread once they are ready. > > > > 1005. Handling partition deletion: The KIP says "RLMM will eventually > > delete these segments by using RemoteStorageManager." Which replica does > > this logic? > > > > This is a good point. When a topic is deleted, it will not have any > > leader/followers to do the cleanup. We will have a cleaner agent on a > > single broker in the cluster to do this cleanup, we plan to add that in > > controller broker. > > > > 1006. "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) > > and user can consume the events(which contain remote-log-segment-id) from > > that topic and clean them up from remote storage. " Not sure if it's worth > > the complexity of adding another topic. Could we just retry? > > > > Sure, we can keep this simpler for now by logging an error after retries. > > We can give users a better way to process this in future. Oneway can be a > > dead letter topic which can be configured by the user. > > > > 1007. RemoteFetchPurgatory: Could we just reuse the existing > > fetchPurgatory? > > > > We have 2 types of delayed operations waiting for 2 different events. > > DelayedFetch waits for new messages from producers. DelayedRemoteFetch > > waits for the remote-storage-read-task to finish. When either of the 2 > > events happens, we only want to notify one type of the delayed operations. > > It would be inefficient to put 2 types of delayed operations in one > > purgatory, as the tryComplete() methods of the delayed operations can be > > triggered by irrelevant events. > > > > > > 1008. Configurations: > > 1008.1 remote.log.retention.ms, remote.log.retention.minutes, > > remote.log.retention.hours: It seems that we just need the ms one. Also, > > are we changing the meaning of existing config log.retention.ms to mean > > the > > local retention? For backward compatibility, it's better to not change the > > meaning of existing configurations. > > > > We agree that we only need remote.log.retention.ms. But, the existing > > Kafka > > configuration > > has 3 properties (log.retention.ms, log.retention.minutes, > > log.retention.hours). We just > > want to keep consistent with the existing properties. > > Existing log.retention.xxxx config is about log retention in broker’s > > storage which is local. It should be easy for users to configure partition > > storage with local retention and remote retention based on their usage. > > > > 1008.2 Should remote.log.storage.enable be at the topic level? > > > > We can introduce topic level config for the same remote.log settings. User > > can set the desired config while creating the topic. > > remote.log.storage.enable property is not allowed to be updated after the > > topic is created. Other remote.log.* properties can be modified. We will > > support flipping remote.log.storage.enable in next versions. > > > > 1009. It would be useful to list all limitations in a separate section: > > compacted topic, JBOD, etc. Also, is changing a topic from delete to > > compact and vice versa allowed when tiering is enabled? > > > > +1 to have limitations in a separate section. We will update the KIP with > > that. > > Topic created with effective value for remote.log.enabled as true, can not > > change its retention policy from delete to compact. > > > > 1010. Thanks for performance numbers. Are those with RocksDB as the cache? > > > > No, We have not yet added RocksDB support. This is based on in-memory map > > representation. We will add that support and update this thread after > > updating the KIP with the numbers. > > > > > > Thanks, > > Satish. > > > > > > On Tue, Jul 21, 2020 at 6:49 AM Jun Rao <j...@confluent.io> wrote: > > > > > Hi, Satish, Ying, Harsha, > > > > > > Thanks for the updated KIP. A few more comments below. > > > > > > 1000. Regarding Colin's question on querying the metadata directly in the > > > remote block store. One issue is that not all block stores offer the > > needed > > > api to query the metadata. For example, S3 only offers an api to list > > > objects under a prefix and this api has the eventual consistency > > semantic. > > > > > > 1001. The KIP described a few scenarios of unclean leader elections. This > > > is very useful, but I am wondering if this is the best approach. My > > > understanding of the proposed approach is to allow the new (unclean) > > leader > > > to take new messages immediately. While this increases availability, it > > > creates the problem that there could be multiple conflicting segments in > > > the remote store for the same offset range. This seems to make it harder > > > for RLMM to determine which archived log segments contain the correct > > data. > > > For example, an archived log segment could at one time be the correct > > data, > > > but be changed to incorrect data after an unclean leader election. An > > > alternative approach is to let the unclean leader use the archived data > > as > > > the source of truth. So, when the new (unclean) leader takes over, it > > first > > > reconciles the local data based on the archived data before taking new > > > messages. This makes the job of RLMM a bit easier since all archived data > > > are considered correct. This increases availability a bit. However, since > > > unclean leader elections are rare, this may be ok. > > > > > > 1002. RemoteStorageManager. > > > 1002.1 There seems to be some inconsistencies in RemoteStorageManager. We > > > pass in RemoteLogSegmentId copyLogSegment(). For all other methods, we > > pass > > > in RemoteLogSegmentMetadata. > > > 1002.2 Is endOffset in RemoteLogSegmentMetadata inclusive or exclusive? > > > 1002.3 It seems that we need an api to get the leaderEpoch history for a > > > partition. > > > 1002.4 Could you define the type of RemoteLogSegmentContext? > > > > > > 1003 RemoteLogMetadataManager > > > 1003.1 I am not sure why we need both of the following methods > > > in RemoteLogMetadataManager. Could we combine them into one that takes in > > > offset and returns RemoteLogSegmentMetadata? > > > RemoteLogSegmentId getRemoteLogSegmentId(TopicPartition > > topicPartition, > > > long offset) throws IOException; > > > RemoteLogSegmentMetadata > > getRemoteLogSegmentMetadata(RemoteLogSegmentId > > > remoteLogSegmentId) throws IOException; > > > 1003.2 There seems to be some inconsistencies in the methods below. I am > > > not sure why one takes RemoteLogSegmentMetadata and the other > > > takes RemoteLogSegmentId. > > > void putRemoteLogSegmentData(RemoteLogSegmentMetadata > > > remoteLogSegmentMetadata) throws IOException; > > > void deleteRemoteLogSegmentMetadata(RemoteLogSegmentId > > > remoteLogSegmentId) throws IOException; > > > 1003.3 In void onServerStarted(final String serverEndpoint), what > > > is serverEndpoint used for? > > > > > > 1004. It would be useful to document how all the new APIs are being used. > > > For example, when is RemoteLogSegmentMetadata.markedForDeletion being set > > > and used? How are > > > RemoteLogMetadataManager.earliestLogOffset/highestLogOffset being used? > > > > > > 1005. Handling partition deletion: The KIP says "RLMM will eventually > > > delete these segments by using RemoteStorageManager." Which replica does > > > this logic? > > > > > > 1006. "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) > > > and user can consume the events(which contain remote-log-segment-id) from > > > that topic and clean them up from remote storage. " Not sure if it's > > worth > > > the complexity of adding another topic. Could we just retry? > > > > > > 1007. RemoteFetchPurgatory: Could we just reuse the existing > > > fetchPurgatory? > > > > > > 1008. Configurations: > > > 1008.1 remote.log.retention.ms, remote.log.retention.minutes, > > > remote.log.retention.hours: It seems that we just need the ms one. Also, > > > are we changing the meaning of existing config log.retention.ms to mean > > > the > > > local retention? For backward compatibility, it's better to not change > > the > > > meaning of existing configurations. > > > 1008.2 Should remote.log.storage.enable be at the topic level? > > > > > > 1009. It would be useful to list all limitations in a separate section: > > > compacted topic, JBOD, etc. Also, is changing a topic from delete to > > > compact and vice versa allowed when tiering is enabled? > > > > > > 1010. Thanks for performance numbers. Are those with RocksDB as the > > cache? > > > > > > Thanks, > > > > > > Jun > > > > > > On Wed, Jul 15, 2020 at 6:12 PM Harsha Ch <harsha...@gmail.com> wrote: > > > > > > > Hi Colin, > > > > Thats not what we said in the previous email. RLMM is > > > > pluggable storage and by running numbers even 1PB data you do not need > > > more > > > > than 10GB local storage. > > > > If in future this becomes a blocker for any users we can revisit but > > this > > > > does not warrant another implementation at this point to push the data > > to > > > > remote storage. > > > > We can ofcourse implement another RLMM that is optional for users to > > > > configure to push to remote. But that doesn't need to be addressed in > > > this > > > > KIP. > > > > > > > > Thanks, > > > > Harsha > > > > > > > > On Wed, Jul 15, 2020 at 5:50 PM Colin McCabe <cmcc...@apache.org> > > wrote: > > > > > > > > > Hi Ying, > > > > > > > > > > Thanks for the response. > > > > > > > > > > It sounds like you agree that storing the metadata in the remote > > > storage > > > > > would be a better design overall. Given that that's true, is there > > any > > > > > reason to include the worse implementation based on RocksDB? > > > > > > > > > > Choosing a long-term metadata store is not something that we should > > do > > > > > lightly. It can take users years to migrate from metadata store to > > the > > > > > other. I also don't think it's realistic or desirable for users to > > > write > > > > > their own metadata stores. Even assuming that they could do a good > > job > > > > at > > > > > this, it would create huge fragmentation in the Kafka ecosystem. > > > > > > > > > > best, > > > > > Colin > > > > > > > > > > > > > > > On Tue, Jul 14, 2020, at 09:39, Ying Zheng wrote: > > > > > > Hi Jun, > > > > > > Hi Colin, > > > > > > > > > > > > Satish and I are still discussing some details about how to handle > > > > > > transactions / producer ids. Satish is going to make some minor > > > changes > > > > > to > > > > > > RLMM API and other parts. Other than that, we have finished > > updating > > > > the > > > > > KIP > > > > > > > > > > > > I agree with Colin that the current design of using rocksDB is not > > > > > > optimal. But this design is simple and should work for almost all > > the > > > > > > existing Kafka users. RLMM is a plugin. Users can replace rocksDB > > > with > > > > > > their own RLMM implementation, if needed. So, I think we can keep > > > > rocksDB > > > > > > for now. What do you think? > > > > > > > > > > > > > > > > > > Thanks, > > > > > > Ying > > > > > > > > > > > > > > > > > > > > > > > > On Tue, Jul 7, 2020 at 10:35 AM Jun Rao <j...@confluent.io> wrote: > > > > > > > > > > > > > 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. > > > > > > > > > > > > > >>>>>> > > > > > > > > > > > > > >>>>>> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
