Hi Till, Good point, in the scenario with the blocking keyed exchange between the writer and committer my idea is to make the committer effectively the global committer. With Sink V2 there is no real difference anymore between the committer and global committer. You are right that everything after the committer would be part of the same failover region but we plan to insert a blocking exchange by default before all of the custom topologies.
Best, Fabian On Thu, Dec 16, 2021 at 11:08 AM Till Rohrmann <trohrm...@apache.org> wrote: > > Hi Fabian, > > quick question on your comment 3. If there is a pipelined data exchange > with a keyBy between the writers/committers and the component that does the > global commit, then there will only be a single failover region. So is it > correct that you assumed blocking data exchanges for the scenario you > described? > > Cheers, > Till > > On Thu, Dec 16, 2021 at 9:23 AM Fabian Paul <fp...@apache.org> wrote: > > > Hi Yun, > > > > Thanks for your fast feedback. Let me clarify your points. > > > > 1. We solve it by using StreamExchangeMode.BATCH before any exchange. > > That obviously doesn’t help with lost TM but we would need to employ > > HA storage for that. Same issue as now and orthogonal. > > > > 2. Extending V1 with V2 or vice versa would require renames of methods > > (since return types are non-optional) and is making API changes. Even > > though Experimental, we want to give connector developers the > > opportunity to provide 1 implementation for all of Flink 1.X. We will > > offer an internal adapter from V1 to V2, 2 sinkTo , and internally > > just have one code-path. > > > > 3. DataStreamSink would act as a unified view on all the operators and > > update them all at once when using setParallelism and so on (setName > > and setUid will receive suffixes per operator). > > Iceberg actually has a different requirement: They want to have a > > committer with parallelism 1 but as a coordinator such that > > embarrassingly parallel pipelines have different fail-over regions. I > > was thinking that in this case, they need to implement a no-op > > committer (that just forwards the committables) and use a post-commit > > topology that achieves that. > > Another option is that they use the preCommit topology and insert a > > constant key-by that forwards all committables to a single committer. > > We are planning to provide building blocks for such pipelines as we > > go. > > > > Best, > > Fabian > > > > On Thu, Dec 16, 2021 at 5:50 AM Yun Gao <yungao...@aliyun.com> wrote: > > > > > > Hi Fabian, > > > > > > Very thanks for the update! I think the latest version in general looks > > good from my side > > > and I think using separate feature interface would be much more easy to > > understand > > > and extend in the future. I have some pending issues on the details > > though: > > > > > > 1. The first one is if we could support end-to-end exactly-once with > > post-committing > > > topology in the batch mode ? Since for the batch mode, currently we > > could only commit > > > all the transactions after the whole job is finished, otherwise if > > there are JM failover or the > > > writer / committer get restarted due to indeterminstic (A -> [B1, B2], > > A, B1 have finished and > > > B2 failed, if -> is rebalance / random / rescale, all of A, B1, B2 > > would restarted), there might > > > be repeat records. Previously one possible thought is to move committer > > and global committer > > > to the operator coordinator, but if it is a topology, we might need > > some other kind of solutions? > > > > > > 2. I also want to have a dobule confirmation with the compatibility: > > since the old sink is also named > > > with Sink, do we want to put the Sink v2 in a new package ? Besides, > > since we might want to keep > > > only have one `sinkTo(Sink<?> sink)` , perhaps we also need to make the > > Sink v1 to be a subclass of > > > Sink v2 and extends the stateful and two-phase-commit sinks, right? > > > > > > 3. I'd like also have a confirmation on ours thoughts with the > > `DataStreamSink` returned by the sinkTo method: > > > The main issue is how do we implement the method like `setParallelism` > > or `setMaxParallelism` since now the sink > > > would be translated to multiple transformations? perhaps we could make > > it the default values for all the transformations > > > for the sink? A related issue would be for iceberg sink, I think it > > would need to have only one committer to avoid the > > > competition of the optimistic locks (which would cause performance > > degradation), then it might need to have N writers > > > with 1 committers, to build such topology, perhaps we might need to add > > new methods to specify the parallelism of > > > the writers and committers separately? > > > > > > Best, > > > Yun > > > > > > > > > ------------------Original Mail ------------------ > > > Sender:Fabian Paul <fp...@apache.org> > > > Send Date:Mon Dec 13 23:59:43 2021 > > > Recipients:dev <dev@flink.apache.org> > > > Subject:Re: [DISCUSS] FLIP-191: Extend unified Sink interface to support > > small file compaction > > >> > > >> Hi all, > > >> > > >> > > >> > > >> After a lot of discussions with different, we received very fruitful > > >> > > >> feedback and reworked the ideas behind this FLIP. Initially, we had > > >> > > >> the impression that the compaction problem is solvable by a single > > >> > > >> topology that we can reuse across different sinks. We now have a > > >> > > >> better understanding that different external systems require different > > >> > > >> compaction mechanism i.e. Hive requires compaction before finally > > >> > > >> registering the file in the metastore or Iceberg compacts the files > > >> > > >> after they have been registered and just lazily compacts them. > > >> > > >> > > >> > > >> Considering all these different views we came up with a design that > > >> > > >> builds upon what @guowei....@gmail.com and @yungao...@aliyun.com have > > >> > > >> proposed at the beginning. We allow inserting custom topologies before > > >> > > >> and after the SinkWriters and Committers. Furthermore, we do not see > > >> > > >> it as a downside. The Sink interfaces that will expose the DataStream > > >> > > >> to the user reside in flink-streaming-java in contrast to the basic > > >> > > >> Sink interfaces that reside fin flink-core deem it to be only used by > > >> > > >> expert users. > > >> > > >> > > >> > > >> Moreover, we also wanted to remove the global committer from the > > >> > > >> unified Sink interfaces and replace it with a custom post-commit > > >> > > >> topology. Unfortunately, we cannot do it without breaking the Sink > > >> > > >> interface since the GlobalCommittables are part of the parameterized > > >> > > >> Sink interface. Thus, we propose building a new Sink V2 interface > > >> > > >> consisting of composable interfaces that do not offer the > > >> > > >> GlobalCommitter anymore. We will implement a utility to extend a Sink > > >> > > >> with post topology that mimics the behavior of the GlobalCommitter. > > >> > > >> The new Sink V2 provides the same sort of methods as the Sink V1 > > >> > > >> interface, so a migration of sinks that do not use the GlobalCommitter > > >> > > >> should be very easy. > > >> > > >> We plan to keep the existing Sink V1 interfaces to not break > > >> > > >> externally built sinks. As part of this FLIP, we migrate all the > > >> > > >> connectors inside of the main repository to the new Sink V2 API. > > >> > > >> > > >> > > >> The FLIP document is also updated and includes the proposed changes. > > >> > > >> > > >> > > >> Looking forward to your feedback, > > >> > > >> Fabian > > >> > > >> > > >> > > >> > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-191%3A+Extend+unified+Sink+interface+to+support+small+file+compaction > > >> > > >> > > >> > > >> > > >> > > >> On Thu, Dec 2, 2021 at 10:15 AM Roman Khachatryan wrote: > > >> > > >> > > > >> > > >> > Thanks for clarifying (I was initially confused by merging state files > > >> > > >> > rather than output files). > > >> > > >> > > > >> > > >> > > At some point, Flink will definitely have some WAL adapter that can > > turn any sink into an exactly-once sink (with some caveats). For now, we > > keep that as an orthogonal solution as it has a rather high price (bursty > > workload with high latency). Ideally, we can keep the compaction > > asynchronously... > > >> > > >> > > > >> > > >> > Yes, that would be something like a WAL. I agree that it would have a > > >> > > >> > different set of trade-offs. > > >> > > >> > > > >> > > >> > > > >> > > >> > Regards, > > >> > > >> > Roman > > >> > > >> > > > >> > > >> > On Mon, Nov 29, 2021 at 3:33 PM Arvid Heise wrote: > > >> > > >> > >> > > >> > > >> > >> > One way to avoid write-read-merge is by wrapping SinkWriter with > > >> > > >> > >> > another one, which would buffer input elements in a temporary > > storage > > >> > > >> > >> > (e.g. local file) until a threshold is reached; after that, it > > would > > >> > > >> > >> > invoke the original SinkWriter. And if a checkpoint barrier > > comes in > > >> > > >> > >> > earlier, it would send written data to some aggregator. > > >> > > >> > >> > > >> > > >> > >> I think perhaps this seems to be a kind of WAL method? Namely we > > first > > >> > > >> > >> write the elements to some WAL logs and persist them on checkpoint > > >> > > >> > >> (in snapshot or remote FS), or we directly write WAL logs to the > > remote > > >> > > >> > >> FS eagerly. > > >> > > >> > >> > > >> > > >> > > At some point, Flink will definitely have some WAL adapter that can > > turn any sink into an exactly-once sink (with some caveats). For now, we > > keep that as an orthogonal solution as it has a rather high price (bursty > > workload with high latency). Ideally, we can keep the compaction > > asynchronously... > > >> > > >> > > > > >> > > >> > > On Mon, Nov 29, 2021 at 8:52 AM Yun Gao wrote: > > >> > > >> > >> > > >> > > >> > >> Hi, > > >> > > >> > >> > > >> > > >> > >> @Roman very sorry for the late response for a long time, > > >> > > >> > >> > > >> > > >> > >> > Merging artifacts from multiple checkpoints would apparently > > >> > > >> > >> require multiple concurrent checkpoints > > >> > > >> > >> > > >> > > >> > >> I think it might not need concurrent checkpoints: suppose some > > >> > > >> > >> operators (like the committer aggregator in the option 2) maintains > > >> > > >> > >> the list of files to merge, it could stores the lists of files to > > merge > > >> > > >> > >> in the states, then after several checkpoints are done and we have > > >> > > >> > >> enough files, we could merge all the files in the list. > > >> > > >> > >> > > >> > > >> > >> > Asynchronous merging in an aggregator would require some > > resolution > > >> > > >> > >> > logic on recovery, so that a merged artifact can be used if the > > >> > > >> > >> > original one was deleted. Otherwise, wouldn't recovery fail > > because > > >> > > >> > >> > some artifacts are missing? > > >> > > >> > >> > We could also defer deletion until the "compacted" checkpoint is > > >> > > >> > >> > subsumed - but isn't it too late, as it will be deleted anyways > > once > > >> > > >> > >> > subsumed? > > >> > > >> > >> > > >> > > >> > >> I think logically we could delete the original files once the > > "compacted" checkpoint > > >> > > >> > >> (which finish merging the compacted files and record it in the > > checkpoint) is completed > > >> > > >> > >> in all the options. If there are failover before we it, we could > > restart the merging and if > > >> > > >> > >> there are failover after it, we could have already recorded the > > files in the checkpoint. > > >> > > >> > >> > > >> > > >> > >> > One way to avoid write-read-merge is by wrapping SinkWriter with > > >> > > >> > >> > another one, which would buffer input elements in a temporary > > storage > > >> > > >> > >> > (e.g. local file) until a threshold is reached; after that, it > > would > > >> > > >> > >> > invoke the original SinkWriter. And if a checkpoint barrier > > comes in > > >> > > >> > >> > earlier, it would send written data to some aggregator. > > >> > > >> > >> > > >> > > >> > >> I think perhaps this seems to be a kind of WAL method? Namely we > > first > > >> > > >> > >> write the elements to some WAL logs and persist them on checkpoint > > >> > > >> > >> (in snapshot or remote FS), or we directly write WAL logs to the > > remote > > >> > > >> > >> FS eagerly. > > >> > > >> > >> > > >> > > >> > >> Sorry if I do not understand correctly somewhere. > > >> > > >> > >> > > >> > > >> > >> Best, > > >> > > >> > >> Yun > > >> > > >> > >> > > >> > > >> > >> > > >> > > >> > >> ------------------------------------------------------------------ > > >> > > >> > >> From:Roman Khachatryan > > >> > > >> > >> Send Time:2021 Nov. 9 (Tue.) 22:03 > > >> > > >> > >> To:dev > > >> > > >> > >> Subject:Re: [DISCUSS] FLIP-191: Extend unified Sink interface to > > support small file compaction > > >> > > >> > >> > > >> > > >> > >> Hi everyone, > > >> > > >> > >> > > >> > > >> > >> Thanks for the proposal and the discussion, I have some remarks: > > >> > > >> > >> (I'm not very familiar with the new Sink API but I thought about > > the > > >> > > >> > >> same problem in context of the changelog state backend) > > >> > > >> > >> > > >> > > >> > >> 1. Merging artifacts from multiple checkpoints would apparently > > >> > > >> > >> require multiple concurrent checkpoints (otherwise, a new > > checkpoint > > >> > > >> > >> won't be started before completing the previous one; and the > > previous > > >> > > >> > >> one can't be completed before durably storing the artifacts). > > However, > > >> > > >> > >> concurrent checkpoints are currently not supported with Unaligned > > >> > > >> > >> checkpoints (this is besides increasing e2e-latency). > > >> > > >> > >> > > >> > > >> > >> 2. Asynchronous merging in an aggregator would require some > > resolution > > >> > > >> > >> logic on recovery, so that a merged artifact can be used if the > > >> > > >> > >> original one was deleted. Otherwise, wouldn't recovery fail because > > >> > > >> > >> some artifacts are missing? > > >> > > >> > >> We could also defer deletion until the "compacted" checkpoint is > > >> > > >> > >> subsumed - but isn't it too late, as it will be deleted anyways > > once > > >> > > >> > >> subsumed? > > >> > > >> > >> > > >> > > >> > >> 3. Writing small files, then reading and merging them for *every* > > >> > > >> > >> checkpoint seems worse than only reading them on recovery. I guess > > I'm > > >> > > >> > >> missing some cases of reading, so to me it would make sense to > > mention > > >> > > >> > >> these cases explicitly in the FLIP motivation section. > > >> > > >> > >> > > >> > > >> > >> 4. One way to avoid write-read-merge is by wrapping SinkWriter with > > >> > > >> > >> another one, which would buffer input elements in a temporary > > storage > > >> > > >> > >> (e.g. local file) until a threshold is reached; after that, it > > would > > >> > > >> > >> invoke the original SinkWriter. And if a checkpoint barrier comes > > in > > >> > > >> > >> earlier, it would send written data to some aggregator. It will > > >> > > >> > >> increase checkpoint delay (async phase) compared to the current > > Flink; > > >> > > >> > >> but not compared to the write-read-merge solution, IIUC. > > >> > > >> > >> Then such "BufferingSinkWriters" could aggregate input elements > > from > > >> > > >> > >> each other, potentially recursively (I mean something like > > >> > > >> > >> > > https://cwiki.apache.org/confluence/download/attachments/173082889/DSTL-DFS-DAG.png > > >> > > >> > >> ) > > >> > > >> > >> > > >> > > >> > >> 5. Reducing the number of files by reducing aggregator parallelism > > as > > >> > > >> > >> opposed to merging on reaching size threshold will likely be less > > >> > > >> > >> optimal and more difficult to configure. OTH, thresholds might be > > more > > >> > > >> > >> difficult to implement and (with recursive merging) would incur > > higher > > >> > > >> > >> latency. Maybe that's also something to decide explicitly or at > > least > > >> > > >> > >> mention in the FLIP. > > >> > > >> > >> > > >> > > >> > >> > > >> > > >> > >> > > >> > > >> > >> Regards, > > >> > > >> > >> Roman > > >> > > >> > >> > > >> > > >> > >> > > >> > > >> > >> On Tue, Nov 9, 2021 at 5:23 AM Reo Lei wrote: > > >> > > >> > >> > > > >> > > >> > >> > Hi Fabian, > > >> > > >> > >> > > > >> > > >> > >> > Thanks for drafting the FLIP and trying to support small file > > compaction. I > > >> > > >> > >> > think this feature is very urgent and valuable for users(at > > least for me). > > >> > > >> > >> > > > >> > > >> > >> > Currently I am trying to support streaming rewrite(compact) for > > Iceberg on > > >> > > >> > >> > PR#3323 . As Steven mentioned, > > >> > > >> > >> > Iceberg sink and compact data through the following steps: > > >> > > >> > >> > Step-1: Some parallel data writer(sinker) to write streaming > > data as files. > > >> > > >> > >> > Step-2: A single parallelism data files committer to commit the > > completed > > >> > > >> > >> > files as soon as possible to make them available. > > >> > > >> > >> > Step-3: Some parallel file rewriter(compactor) to collect > > committed files > > >> > > >> > >> > from multiple checkpoints, and rewriter(compact) them together > > once the > > >> > > >> > >> > total file size or number of files reach the threshold. > > >> > > >> > >> > Step-4: A single parallelism rewrite(compact) result committer > > to commit > > >> > > >> > >> > the rewritten(compacted) files to replace the old files and make > > them > > >> > > >> > >> > available. > > >> > > >> > >> > > > >> > > >> > >> > > > >> > > >> > >> > If Flink want to support small file compaction, some key point I > > think is > > >> > > >> > >> > necessary: > > >> > > >> > >> > > > >> > > >> > >> > 1, Compact files from multiple checkpoints. > > >> > > >> > >> > I totally agree with Jingsong, because completed file size > > usually could > > >> > > >> > >> > not reach the threshold in a single checkpoint. Especially for > > partitioned > > >> > > >> > >> > table, we need to compact the files of each partition, but > > usually the file > > >> > > >> > >> > size of each partition will be different and may not reach the > > merge > > >> > > >> > >> > threshold. If we compact these files, in a single checkpoint, > > regardless of > > >> > > >> > >> > whether the total file size reaches the threshold, then the > > value of > > >> > > >> > >> > compacting will be diminished and we will still get small files > > because > > >> > > >> > >> > these compacted files are not reach to target size. So we need > > the > > >> > > >> > >> > compactor to collect committed files from multiple checkpoints > > and compact > > >> > > >> > >> > them until they reach the threshold. > > >> > > >> > >> > > > >> > > >> > >> > 2, Separate write phase and compact phase. > > >> > > >> > >> > Users usually hope the data becomes available as soon as > > possible, and the > > >> > > >> > >> > end-to-end latency is very important. I think we need to > > separate the > > >> > > >> > >> > write and compact phase. For the write phase, there include the > > Step-1 > > >> > > >> > >> > and Step-2, we sink data as file and commit it pre checkpoint > > and regardless > > >> > > >> > >> > of whether the file size it is. That could ensure the data will > > be > > >> > > >> > >> > available ASAP. For the compact phase, there include the Step-3 > > >> > > >> > >> > and Step-4, the compactor should collect committed files from > > multiple > > >> > > >> > >> > checkpoints and compact them asynchronously once they reach the > > threshold, > > >> > > >> > >> > and the compact committer will commit the compaction result in > > the next > > >> > > >> > >> > checkpoint. We compact the committed files asynchronously > > because we don't > > >> > > >> > >> > want the compaction to affect the data sink or the whole > > pipeline. > > >> > > >> > >> > > > >> > > >> > >> > 3, Exactly once guarantee between write and compact phase. > > >> > > >> > >> > Once we separate write phase and compact phase, we need to > > consider > > >> > > >> > >> > how to guarantee > > >> > > >> > >> > the exact once semantic between two phases. We should not lose > > any data or > > >> > > >> > >> > files on the compactor(Step-3) in any case and cause the > > compaction result > > >> > > >> > >> > to be inconsistent with before. I think flink should provide an > > easy-to-use > > >> > > >> > >> > interface to make that easier. > > >> > > >> > >> > > > >> > > >> > >> > 4, Metadata operation and compaction result validation. > > >> > > >> > >> > In the compact phase, there may be not only compact files, but > > also a lot > > >> > > >> > >> > of metadata operations, such as the iceberg needing to > > read/write manifest > > >> > > >> > >> > and do MOR. And we need some interface to support users to do > > some > > >> > > >> > >> > validation of the compaction result. I think these points should > > be > > >> > > >> > >> > considered when we design the compaction API. > > >> > > >> > >> > > > >> > > >> > >> > > > >> > > >> > >> > Back to FLIP-191, option 1 looks very complicated while option 2 > > is > > >> > > >> > >> > relatively simple, but neither of these two solutions separates > > the write > > >> > > >> > >> > phase from the compact phase. So I think we should consider the > > points I > > >> > > >> > >> > mentioned above. And if you have any other questions you can > > always feel > > >> > > >> > >> > free to reach out to me! > > >> > > >> > >> > > > >> > > >> > >> > BR, > > >> > > >> > >> > Reo > > >> > > >> > >> > > > >> > > >> > >> > Fabian Paul 于2021年11月8日周一 下午7:59写道： > > >> > > >> > >> > > > >> > > >> > >> > > Hi all, > > >> > > >> > >> > > > > >> > > >> > >> > > Thanks for the lively discussions. I am really excited to see > > so many > > >> > > >> > >> > > people > > >> > > >> > >> > > participating in this thread. It also underlines the need that > > many people > > >> > > >> > >> > > would > > >> > > >> > >> > > like to see a solution soon. > > >> > > >> > >> > > > > >> > > >> > >> > > I have updated the FLIP and removed the parallelism > > configuration because > > >> > > >> > >> > > it is > > >> > > >> > >> > > unnecessary since users can configure a constant exchange key > > to send all > > >> > > >> > >> > > committables to only one committable aggregator. > > >> > > >> > >> > > > > >> > > >> > >> > > > > >> > > >> > >> > > 1. Burden for developers w.r.t batch stream unification. > > >> > > >> > >> > > > > >> > > >> > >> > > @yun @guowei, from a theoretical point you are right about > > exposing the > > >> > > >> > >> > > DataStream > > >> > > >> > >> > > API in the sink users have the full power to write correct > > batch and > > >> > > >> > >> > > streaming > > >> > > >> > >> > > sinks. I think in reality a lot of users still struggle to > > build pipelines > > >> > > >> > >> > > with > > >> > > >> > >> > > i.e. the operator pipeline which works correct in streaming > > and batch mode. > > >> > > >> > >> > > Another problem I see is by exposing more deeper concepts is > > that we > > >> > > >> > >> > > cannot do > > >> > > >> > >> > > any optimization because we cannot reason about how sinks are > > built in the > > >> > > >> > >> > > future. > > >> > > >> > >> > > > > >> > > >> > >> > > We should also try to steer users towards using only > > `Functions` to give > > >> > > >> > >> > > us more > > >> > > >> > >> > > flexibility to swap the internal operator representation. I > > agree with > > >> > > >> > >> > > @yun we > > >> > > >> > >> > > should try to make the `ProcessFunction` more versatile to > > work on that > > >> > > >> > >> > > goal but > > >> > > >> > >> > > I see this as unrelated to the FLIP. > > >> > > >> > >> > > > > >> > > >> > >> > > > > >> > > >> > >> > > 2. Regarding Commit / Global commit > > >> > > >> > >> > > > > >> > > >> > >> > > I envision the global committer to be specific depending on > > the data lake > > >> > > >> > >> > > solution you want to write to. However, it is entirely > > orthogonal to the > > >> > > >> > >> > > compaction. > > >> > > >> > >> > > Currently, I do not expect any changes w.r.t the Global commit > > introduces > > >> > > >> > >> > > by > > >> > > >> > >> > > this FLIP. > > >> > > >> > >> > > > > >> > > >> > >> > > > > >> > > >> > >> > > 3. Regarding the case of trans-checkpoints merging > > >> > > >> > >> > > > > >> > > >> > >> > > @yun, as user, I would expect that if the committer receives > > in a > > >> > > >> > >> > > checkpoint files > > >> > > >> > >> > > to merge/commit that these are also finished when the > > checkpoint finishes. > > >> > > >> > >> > > I think all sinks rely on this principle currently i.e., > > KafkaSink needs to > > >> > > >> > >> > > commit all open transactions until the next checkpoint can > > happen. > > >> > > >> > >> > > > > >> > > >> > >> > > Maybe in the future, we can somehow move the Committer#commit > > call to an > > >> > > >> > >> > > asynchronous execution, but we should discuss it as a separate > > thread. > > >> > > >> > >> > > > > >> > > >> > >> > > > We probably should first describe the different causes of > > small files and > > >> > > >> > >> > > > what problems was this proposal trying to solve. I wrote a > > data shuffling > > >> > > >> > >> > > > proposal [1] for Flink Iceberg sink (shared with Iceberg > > community [2]). > > >> > > >> > >> > > It > > >> > > >> > >> > > > can address small files problems due to skewed data > > distribution across > > >> > > >> > >> > > > Iceberg table partitions. Streaming shuffling before writers > > (to files) > > >> > > >> > >> > > is > > >> > > >> > >> > > > typically more efficient than post-write file compaction > > (which involves > > >> > > >> > >> > > > read-merge-write). It is usually cheaper to prevent a > > problem (small > > >> > > >> > >> > > files) > > >> > > >> > >> > > > than fixing it. > > >> > > >> > >> > > > > >> > > >> > >> > > > > >> > > >> > >> > > @steven you are raising a good point, although I think only > > using a > > >> > > >> > >> > > customizable > > >> > > >> > >> > > shuffle won't address the generation of small files. One > > assumption is that > > >> > > >> > >> > > at least the sink generates one file per subtask, which can > > already be too > > >> > > >> > >> > > many. > > >> > > >> > >> > > Another problem is that with low checkpointing intervals, the > > files do not > > >> > > >> > >> > > meet > > >> > > >> > >> > > the required size. The latter point is probably addressable by > > changing the > > >> > > >> > >> > > checkpoint interval, which might be inconvenient for some > > users. > > >> > > >> > >> > > > > >> > > >> > >> > > > The sink coordinator checkpoint problem (mentioned in option > > 1) would be > > >> > > >> > >> > > > great if Flink can address it. In the spirit of source > > >> > > >> > >> > > (enumerator-reader) > > >> > > >> > >> > > > and sink (writer-coordinator) duality, sink coordinator > > checkpoint should > > >> > > >> > >> > > > happen after the writer operator. This would be a natural > > fit to support > > >> > > >> > >> > > > global committer in FLIP-143. It is probably an orthogonal > > matter to this > > >> > > >> > >> > > > proposal. > > >> > > >> > >> > > > > >> > > >> > >> > > > > >> > > >> > >> > > To me the question here is what are the benefits of having a > > coordinator in > > >> > > >> > >> > > comparison to a global committer/aggregator operator. > > >> > > >> > >> > > > > >> > > >> > >> > > > Personally, I am usually in favor of keeping streaming > > ingestion (to data > > >> > > >> > >> > > > lake) relatively simple and stable. Also sometimes > > compaction and sorting > > >> > > >> > >> > > > are performed together in data rewrite maintenance jobs to > > improve read > > >> > > >> > >> > > > performance. In that case, the value of compacting (in Flink > > streaming > > >> > > >> > >> > > > ingestion) diminishes. > > >> > > >> > >> > > > > >> > > >> > >> > > > > >> > > >> > >> > > I agree it is always possible to have scheduled maintenance > > jobs keeping > > >> > > >> > >> > > care of > > >> > > >> > >> > > your data i.e., doing compaction. Unfortunately, the downside > > is that you > > >> > > >> > >> > > have to your data after it is already available for other > > downstream > > >> > > >> > >> > > consumers. > > >> > > >> > >> > > I guess this can lead to all kinds of visibility problems. I > > am also > > >> > > >> > >> > > surprised that > > >> > > >> > >> > > you personally are a fan of this approach and, on the other > > hand, are > > >> > > >> > >> > > developing > > >> > > >> > >> > > the Iceberg sink, which goes somewhat against your mentioned > > principle of > > >> > > >> > >> > > keeping > > >> > > >> > >> > > the sink simple. > > >> > > >> > >> > > > > >> > > >> > >> > > > Currently, it is unclear from the doc and this thread where > > the > > >> > > >> > >> > > compaction > > >> > > >> > >> > > > is actually happening. Jingsong's reply described one model > > >> > > >> > >> > > > writer (parallel) -> aggregator (single-parallelism > > compaction planner) > > >> > > >> > >> > > -> > > >> > > >> > >> > > > compactor (parallel) -> global committer (single-parallelism) > > >> > > >> > >> > > > > >> > > >> > >> > > > > >> > > >> > >> > > My idea of the topology is very similar to the one outlined by > > Jinsong. The > > >> > > >> > >> > > compaction will happen in the committer operator. > > >> > > >> > >> > > > > >> > > >> > >> > > > > > >> > > >> > >> > > > In the Iceberg community, the following model has been > > discussed. It is > > >> > > >> > >> > > > better for Iceberg because it won't delay the data > > availability. > > >> > > >> > >> > > > writer (parallel) -> global committer for append (single > > parallelism) -> > > >> > > >> > >> > > > compactor (parallel) -> global committer for rewrite commit > > (single > > >> > > >> > >> > > > parallelism) > > >> > > >> > >> > > > > >> > > >> > >> > > > > >> > > >> > >> > > From a quick glimpse, it seems that the exact same topology is > > possible to > > >> > > >> > >> > > express with the committable aggregator, but this definitely > > depends on > > >> > > >> > >> > > the exact > > >> > > >> > >> > > setup. > > >> > > >> > >> > > > > >> > > >> > >> > > Best, > > >> > > >> > >> > > Fabian > > >> > > >> > >> > >
