Re: [DISCUSS] KIP-405: Kafka Tiered Storage

[Jun Rao]

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.
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>>
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>