Re: Source alignment for Iceberg
add dev@ group to the thread as Thomas suggested Arvid, The scenario 3 (Dynamic assignment + temporary no split) in the FLIP-180 (idleness) can happen to Iceberg source alignment, as readers can be temporarily starved due to the holdback by the enumerator when assigning new splits upon request. Totally agree that we should decouple this discussion with the FLIP-217, which addresses the split level watermark alignment problem as a follow-up of FLIP-182 Becket, Yes, currently Iceberg source implemented the alignment leveraging the dynamic split assignment from FLIP-27 design. Basically, the enumerator can hold back split assignments to readers when necessary. Everything are centralized in the enumerator: (1) watermark extraction and aggregation (2) alignment decision and execution The motivation of this discussion is to see if Iceberg source can leverage some of the watermark alignment solutions (like FLIP-182) from Flink framework. E.g., as mentioned in the doc, Iceberg source can potentially leverage the FLIP-182 framework to do the watermark extraction and aggregation. For the alignment decision and execution, we can keep them in the centralized enumerator. Thanks, Steven On Thu, Apr 28, 2022 at 2:05 AM Becket Qin wrote: > Hi Steven, > > Thanks for pulling me into this thread. I think the timestamp > alignment use case here is a good example of what FLIP-27 was designed for. > > Technically speaking, Iceberg source can already implement the timestamp > alignment in the Flink new source even without FLIP-182. However, I > understand the rationale here because timestamp alignment is also trying to > orchestrate the consumption of splits. However, it looks like FLIP-182 was > not designed in a way that it can be easily extended for other use cases. > It may probably worth thinking of a more general mechanism to answer the > following questions: > > 1. What information whose source of truth is the Flink framework should be > exposed to the SplitEnumerator and SourceReader? And how? > 2. What control actions in the Flink framework are worth exposing to the > SplitEnumerators and SourceReaders? And how? > > In the context of timestamp alignment, the first question is more > relevant. For example, instead of hardcode the ReportWatermarkEvent > handling logic in the SourceCoordinator, should we expose this to the > SplitEnumerator? So basically there will be some information, such as > subtask local watermark, whose source of truth is Flink runtime, but useful > to the user provided pluggables. > > I think there are a few control flow patterns to make a complete design: > > a. Framework space information (e.g. watermark) --> User space Pluggables > (e.g. SplitEnumerator) --> User space Actions (e.g. Pause reading a split). > b. Framework space information (e.g. task failure) --> User space > pluggables (e.g. SplitEnumerator) --> Framework space actions (e.g. exit > the job) > c. User space information (e.g. a custom workload metric) --> User space > pluggables (e.g. SplitEnumerator) --> User space actions (e.g. rebalance > the workload across the source readers). > d. Use space information (e.g. a custom stopping event in the stream) --> > User space pluggables (e.g. SplitEnumerator) --> Framework space actions > (e.g. stop the job). > > So basically for any user provided pluggables, the input information may > either come from another user provided logic or from the framework, and > after receiving that information, the pluggable may either want the > framework or another pluggable to take an action. So this gives the above 4 > combinations. > > In our case, when the pluggables are SplitEnumerator and SourceReader, the > control flows that only involve user space actions are fully supported. But > it seems that when it comes to control flows involving framework space > information, some of the information has not been exposed to the pluggable, > and some framework actions might also be missing. > > Thanks, > > Jiangjie (Becket) Qin > > On Thu, Apr 28, 2022 at 3:44 PM Arvid Heise wrote: > >> Hi folks, >> >> quick input from my side. I think this is from the implementation >> perspective what Piotr and I had in mind for a global min watermark that >> helps in idleness cases. See also point 3 in >> https://cwiki.apache.org/confluence/display/FLINK/FLIP-180%3A+Adjust+StreamStatus+and+Idleness+definition >> . >> >> Basically, we would like to empower source enumerators to determine the >> global min watermark for all source readers factoring in even future >> splits. Not all sources can supply that information (think of a general >> file source) but most should be able to. Basically, Flink should know for a >> given source at a given point in time what the min watermark across all >> source subtasks is. >> >> Here is some background: >> In the context of idleness, we can deterministically advance the >> watermark. In the pre-FLIP-27 era, we had heuristic approaches in sources >> to switch to idleness and t
Re: Source alignment for Iceberg
Hi Steven, Isn't this redundant to FLIP-182 and FLIP-217? Can not Iceberg just emit all splits and let FLIP-182/FLIP-217 handle the watermark alignment and block the splits that are too much into the future? I can see this being an issue if the existence of too many blocked splits is occupying too many resources. If that's the case, indeed SourceCoordinator/SplitEnumerator would have to decide on some basis how many and which splits to assign in what order. But in that case I'm not sure how much you could use from FLIP-182 and FLIP-217. They seem somehow orthogonal to me, operating on different levels. FLIP-182 and FLIP-217 are working with whatever splits have already been generated and assigned. You could leverage FLIP-182 and FLIP-217 and take care of only the problem to limit the number of parallel active splits. And here I'm not sure if it would be worth generalising a solution across different connectors. Regarding the global watermark, I made a related comment sometime ago about it [1]. It sounds to me like you also need to solve this problem, otherwise Iceberg users will encounter late records in case of some race conditions between assigning new splits and completions of older. Best, Piotrek [1] https://issues.apache.org/jira/browse/FLINK-21871?focusedCommentId=17495545&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-17495545 pon., 2 maj 2022 o 04:26 Steven Wu napisał(a): > add dev@ group to the thread as Thomas suggested > > Arvid, > > The scenario 3 (Dynamic assignment + temporary no split) in the FLIP-180 > (idleness) can happen to Iceberg source alignment, as readers can be > temporarily starved due to the holdback by the enumerator when assigning > new splits upon request. > > Totally agree that we should decouple this discussion with the FLIP-217, > which addresses the split level watermark alignment problem as a follow-up > of FLIP-182 > > Becket, > > Yes, currently Iceberg source implemented the alignment leveraging the > dynamic split assignment from FLIP-27 design. Basically, the enumerator can > hold back split assignments to readers when necessary. Everything are > centralized in the enumerator: (1) watermark extraction and aggregation (2) > alignment decision and execution > > The motivation of this discussion is to see if Iceberg source can leverage > some of the watermark alignment solutions (like FLIP-182) from Flink > framework. E.g., as mentioned in the doc, Iceberg source can potentially > leverage the FLIP-182 framework to do the watermark extraction and > aggregation. For the alignment decision and execution, we can keep them in > the centralized enumerator. > > Thanks, > Steven > > On Thu, Apr 28, 2022 at 2:05 AM Becket Qin wrote: > > > Hi Steven, > > > > Thanks for pulling me into this thread. I think the timestamp > > alignment use case here is a good example of what FLIP-27 was designed > for. > > > > Technically speaking, Iceberg source can already implement the timestamp > > alignment in the Flink new source even without FLIP-182. However, I > > understand the rationale here because timestamp alignment is also trying > to > > orchestrate the consumption of splits. However, it looks like FLIP-182 > was > > not designed in a way that it can be easily extended for other use cases. > > It may probably worth thinking of a more general mechanism to answer the > > following questions: > > > > 1. What information whose source of truth is the Flink framework should > be > > exposed to the SplitEnumerator and SourceReader? And how? > > 2. What control actions in the Flink framework are worth exposing to the > > SplitEnumerators and SourceReaders? And how? > > > > In the context of timestamp alignment, the first question is more > > relevant. For example, instead of hardcode the ReportWatermarkEvent > > handling logic in the SourceCoordinator, should we expose this to the > > SplitEnumerator? So basically there will be some information, such as > > subtask local watermark, whose source of truth is Flink runtime, but > useful > > to the user provided pluggables. > > > > I think there are a few control flow patterns to make a complete design: > > > > a. Framework space information (e.g. watermark) --> User space Pluggables > > (e.g. SplitEnumerator) --> User space Actions (e.g. Pause reading a > split). > > b. Framework space information (e.g. task failure) --> User space > > pluggables (e.g. SplitEnumerator) --> Framework space actions (e.g. exit > > the job) > > c. User space information (e.g. a custom workload metric) --> User space > > pluggables (e.g. SplitEnumerator) --> User space actions (e.g. rebalance > > the workload across the source readers). > > d. Use space information (e.g. a custom stopping event in the stream) --> > > User space pluggables (e.g. SplitEnumerator) --> Framework space actions > > (e.g. stop the job). > > > > So basically for any user provided pluggables, the input information may > > either come from another use
Re: Source alignment for Iceberg
Hey Piotr, I think the mechanism FLIP-182 provided is a reasonable default one, which ensures the watermarks are only drifted by an upper bound. However, admittedly there are also other strategies for different purposes. In the Iceberg case, I am not sure if a static strictly allowed watermark drift is desired. The source might just want to finish reading the assigned splits as fast as possible. And it is OK to have a drift of "one split", instead of a fixed time period. As another example, if there are some fast readers whose splits are always throttled, while the other slow readers are struggling to keep up with the rest of the splits, the split enumerator may decide to reassign the slow splits so all the readers have something to read. This would need the SplitEnumerator to be aware of the watermark progress on each reader. So it seems useful to expose the WatermarkAlignmentEvent information to the SplitEnumerator as well. Thanks, Jiangjie (Becket) Qin On Tue, May 3, 2022 at 7:58 PM Piotr Nowojski wrote: > Hi Steven, > > Isn't this redundant to FLIP-182 and FLIP-217? Can not Iceberg just emit > all splits and let FLIP-182/FLIP-217 handle the watermark alignment and > block the splits that are too much into the future? I can see this being an > issue if the existence of too many blocked splits is occupying too many > resources. > > If that's the case, indeed SourceCoordinator/SplitEnumerator would have to > decide on some basis how many and which splits to assign in what order. But > in that case I'm not sure how much you could use from FLIP-182 and > FLIP-217. They seem somehow orthogonal to me, operating on different > levels. FLIP-182 and FLIP-217 are working with whatever splits have already > been generated and assigned. You could leverage FLIP-182 and FLIP-217 and > take care of only the problem to limit the number of parallel active > splits. And here I'm not sure if it would be worth generalising a solution > across different connectors. > > Regarding the global watermark, I made a related comment sometime ago > about it [1]. It sounds to me like you also need to solve this problem, > otherwise Iceberg users will encounter late records in case of some race > conditions between assigning new splits and completions of older. > > Best, > Piotrek > > [1] > https://issues.apache.org/jira/browse/FLINK-21871?focusedCommentId=17495545&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-17495545 > > pon., 2 maj 2022 o 04:26 Steven Wu napisał(a): > >> add dev@ group to the thread as Thomas suggested >> >> Arvid, >> >> The scenario 3 (Dynamic assignment + temporary no split) in the FLIP-180 >> (idleness) can happen to Iceberg source alignment, as readers can be >> temporarily starved due to the holdback by the enumerator when assigning >> new splits upon request. >> >> Totally agree that we should decouple this discussion with the FLIP-217, >> which addresses the split level watermark alignment problem as a follow-up >> of FLIP-182 >> >> Becket, >> >> Yes, currently Iceberg source implemented the alignment leveraging the >> dynamic split assignment from FLIP-27 design. Basically, the enumerator >> can >> hold back split assignments to readers when necessary. Everything are >> centralized in the enumerator: (1) watermark extraction and aggregation >> (2) >> alignment decision and execution >> >> The motivation of this discussion is to see if Iceberg source can leverage >> some of the watermark alignment solutions (like FLIP-182) from Flink >> framework. E.g., as mentioned in the doc, Iceberg source can potentially >> leverage the FLIP-182 framework to do the watermark extraction and >> aggregation. For the alignment decision and execution, we can keep them in >> the centralized enumerator. >> >> Thanks, >> Steven >> >> On Thu, Apr 28, 2022 at 2:05 AM Becket Qin wrote: >> >> > Hi Steven, >> > >> > Thanks for pulling me into this thread. I think the timestamp >> > alignment use case here is a good example of what FLIP-27 was designed >> for. >> > >> > Technically speaking, Iceberg source can already implement the timestamp >> > alignment in the Flink new source even without FLIP-182. However, I >> > understand the rationale here because timestamp alignment is also >> trying to >> > orchestrate the consumption of splits. However, it looks like FLIP-182 >> was >> > not designed in a way that it can be easily extended for other use >> cases. >> > It may probably worth thinking of a more general mechanism to answer the >> > following questions: >> > >> > 1. What information whose source of truth is the Flink framework should >> be >> > exposed to the SplitEnumerator and SourceReader? And how? >> > 2. What control actions in the Flink framework are worth exposing to the >> > SplitEnumerators and SourceReaders? And how? >> > >> > In the context of timestamp alignment, the first question is more >> > relevant. For example, instead of hardcode the ReportWatermarkEvent >> > handl
Re: Source alignment for Iceberg
Piotr, thanks a lot for your feedback. > I can see this being an issue if the existence of too many blocked splits is occupying too many resources. This is not desirable. Eagerly assigning many splits to a reader can defeat the benefits of pull based dynamic split assignments. Iceberg readers request one split at a time upon start or completion of a split. Dynamic split assignment is better for work sharing/stealing as Becket mentioned. Limiting number of active splits can be handled by the FLIP-27 Iceberg source and is somewhat orthogonal to watermark alignment. > Can not Iceberg just emit all splits and let FLIP-182/FLIP-217 handle the watermark alignment and block the splits that are too much into the future? The enumerator just assigns the next split to the requesting reader instead of holding back the split assignment. Let the reader handle the pause (if the file split requires alignment wait). This strategy might work and leverage more from the framework. We probably need the following to make this work * extract watermark/timestamp only at the completion of a split (not at record level). Because records in a file aren't probably not sorted by the timestamp field, the pause or watermark advancement is probably better done at file level. * source readers checkpoint the watermark. otherwise, upon restart readers won't be able to determine the local watermark and pause for alignment. We don't want to emit records upon restart due to unknown watermark info. All, Any opinion on different timestamp for source alignment (vs Flink application watermark)? For Iceberg source, we might want to enforce alignment on kafka timestamp but Flink application watermark may use event time field from payload. Thanks, Steven On Wed, May 4, 2022 at 7:02 AM Becket Qin wrote: > Hey Piotr, > > I think the mechanism FLIP-182 provided is a reasonable default one, which > ensures the watermarks are only drifted by an upper bound. However, > admittedly there are also other strategies for different purposes. > > In the Iceberg case, I am not sure if a static strictly allowed watermark > drift is desired. The source might just want to finish reading the assigned > splits as fast as possible. And it is OK to have a drift of "one split", > instead of a fixed time period. > > As another example, if there are some fast readers whose splits are always > throttled, while the other slow readers are struggling to keep up with the > rest of the splits, the split enumerator may decide to reassign the slow > splits so all the readers have something to read. This would need the > SplitEnumerator to be aware of the watermark progress on each reader. So it > seems useful to expose the WatermarkAlignmentEvent information to the > SplitEnumerator as well. > > Thanks, > > Jiangjie (Becket) Qin > > > > On Tue, May 3, 2022 at 7:58 PM Piotr Nowojski > wrote: > > > Hi Steven, > > > > Isn't this redundant to FLIP-182 and FLIP-217? Can not Iceberg just emit > > all splits and let FLIP-182/FLIP-217 handle the watermark alignment and > > block the splits that are too much into the future? I can see this being > an > > issue if the existence of too many blocked splits is occupying too many > > resources. > > > > If that's the case, indeed SourceCoordinator/SplitEnumerator would have > to > > decide on some basis how many and which splits to assign in what order. > But > > in that case I'm not sure how much you could use from FLIP-182 and > > FLIP-217. They seem somehow orthogonal to me, operating on different > > levels. FLIP-182 and FLIP-217 are working with whatever splits have > already > > been generated and assigned. You could leverage FLIP-182 and FLIP-217 and > > take care of only the problem to limit the number of parallel active > > splits. And here I'm not sure if it would be worth generalising a > solution > > across different connectors. > > > > Regarding the global watermark, I made a related comment sometime ago > > about it [1]. It sounds to me like you also need to solve this problem, > > otherwise Iceberg users will encounter late records in case of some race > > conditions between assigning new splits and completions of older. > > > > Best, > > Piotrek > > > > [1] > > > https://issues.apache.org/jira/browse/FLINK-21871?focusedCommentId=17495545&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-17495545 > > > > pon., 2 maj 2022 o 04:26 Steven Wu napisał(a): > > > >> add dev@ group to the thread as Thomas suggested > >> > >> Arvid, > >> > >> The scenario 3 (Dynamic assignment + temporary no split) in the FLIP-180 > >> (idleness) can happen to Iceberg source alignment, as readers can be > >> temporarily starved due to the holdback by the enumerator when assigning > >> new splits upon request. > >> > >> Totally agree that we should decouple this discussion with the FLIP-217, > >> which addresses the split level watermark alignment problem as a > follow-up > >> of FLIP-182 > >> > >> Becket, > >> > >>
Re: Source alignment for Iceberg
Ok, I see. Thanks to both of you for the explanation. Do we need changes to Apache Flink for this feature? Can it be implemented in the Sources without changes in the framework? I presume source can access min/max watermark from the split, so as long as it also knows exactly which splits have finished, it would know which splits to hold back. Best, Piotrek śr., 4 maj 2022 o 20:03 Steven Wu napisał(a): > Piotr, thanks a lot for your feedback. > > > I can see this being an issue if the existence of too many blocked > splits is occupying too many resources. > > This is not desirable. Eagerly assigning many splits to a reader can > defeat the benefits of pull based dynamic split assignments. Iceberg > readers request one split at a time upon start or completion of a split. > Dynamic split assignment is better for work sharing/stealing as Becket > mentioned. Limiting number of active splits can be handled by the FLIP-27 > Iceberg source and is somewhat orthogonal to watermark alignment. > > > Can not Iceberg just emit all splits and let FLIP-182/FLIP-217 handle > the watermark alignment and block the splits that are too much into the > future? > > The enumerator just assigns the next split to the requesting reader > instead of holding back the split assignment. Let the reader handle the > pause (if the file split requires alignment wait). This strategy might > work and leverage more from the framework. > > We probably need the following to make this work > * extract watermark/timestamp only at the completion of a split (not at > record level). Because records in a file aren't probably not sorted by the > timestamp field, the pause or watermark advancement is probably better done > at file level. > * source readers checkpoint the watermark. otherwise, upon restart readers > won't be able to determine the local watermark and pause for alignment. We > don't want to emit records upon restart due to unknown watermark info. > > All, > > Any opinion on different timestamp for source alignment (vs Flink > application watermark)? For Iceberg source, we might want to enforce > alignment on kafka timestamp but Flink application watermark may use event > time field from payload. > > Thanks, > Steven > > On Wed, May 4, 2022 at 7:02 AM Becket Qin wrote: > >> Hey Piotr, >> >> I think the mechanism FLIP-182 provided is a reasonable default one, which >> ensures the watermarks are only drifted by an upper bound. However, >> admittedly there are also other strategies for different purposes. >> >> In the Iceberg case, I am not sure if a static strictly allowed watermark >> drift is desired. The source might just want to finish reading the >> assigned >> splits as fast as possible. And it is OK to have a drift of "one split", >> instead of a fixed time period. >> >> As another example, if there are some fast readers whose splits are always >> throttled, while the other slow readers are struggling to keep up with the >> rest of the splits, the split enumerator may decide to reassign the slow >> splits so all the readers have something to read. This would need the >> SplitEnumerator to be aware of the watermark progress on each reader. So >> it >> seems useful to expose the WatermarkAlignmentEvent information to the >> SplitEnumerator as well. >> >> Thanks, >> >> Jiangjie (Becket) Qin >> >> >> >> On Tue, May 3, 2022 at 7:58 PM Piotr Nowojski >> wrote: >> >> > Hi Steven, >> > >> > Isn't this redundant to FLIP-182 and FLIP-217? Can not Iceberg just emit >> > all splits and let FLIP-182/FLIP-217 handle the watermark alignment and >> > block the splits that are too much into the future? I can see this >> being an >> > issue if the existence of too many blocked splits is occupying too many >> > resources. >> > >> > If that's the case, indeed SourceCoordinator/SplitEnumerator would have >> to >> > decide on some basis how many and which splits to assign in what order. >> But >> > in that case I'm not sure how much you could use from FLIP-182 and >> > FLIP-217. They seem somehow orthogonal to me, operating on different >> > levels. FLIP-182 and FLIP-217 are working with whatever splits have >> already >> > been generated and assigned. You could leverage FLIP-182 and FLIP-217 >> and >> > take care of only the problem to limit the number of parallel active >> > splits. And here I'm not sure if it would be worth generalising a >> solution >> > across different connectors. >> > >> > Regarding the global watermark, I made a related comment sometime ago >> > about it [1]. It sounds to me like you also need to solve this problem, >> > otherwise Iceberg users will encounter late records in case of some race >> > conditions between assigning new splits and completions of older. >> > >> > Best, >> > Piotrek >> > >> > [1] >> > >> https://issues.apache.org/jira/browse/FLINK-21871?focusedCommentId=17495545&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-17495545 >> > >> > pon., 2 maj 2022 o 04:26 Steven Wu napis
Re: Source alignment for Iceberg
Piotr, With FLIP-27, Iceberg source already implemented alignment by tracking watermark and holding back split assignment when necessary. The purpose of this discussion is to see if Iceberg source can leverage some of the watermark alignment work from Flink framework. Thanks, Steven On Thu, May 5, 2022 at 1:10 AM Piotr Nowojski wrote: > Ok, I see. Thanks to both of you for the explanation. > > Do we need changes to Apache Flink for this feature? Can it be implemented > in the Sources without changes in the framework? I presume source can > access min/max watermark from the split, so as long as it also knows > exactly which splits have finished, it would know which splits to hold back. > > Best, > Piotrek > > śr., 4 maj 2022 o 20:03 Steven Wu napisał(a): > >> Piotr, thanks a lot for your feedback. >> >> > I can see this being an issue if the existence of too many blocked >> splits is occupying too many resources. >> >> This is not desirable. Eagerly assigning many splits to a reader can >> defeat the benefits of pull based dynamic split assignments. Iceberg >> readers request one split at a time upon start or completion of a split. >> Dynamic split assignment is better for work sharing/stealing as Becket >> mentioned. Limiting number of active splits can be handled by the FLIP-27 >> Iceberg source and is somewhat orthogonal to watermark alignment. >> >> > Can not Iceberg just emit all splits and let FLIP-182/FLIP-217 handle >> the watermark alignment and block the splits that are too much into the >> future? >> >> The enumerator just assigns the next split to the requesting reader >> instead of holding back the split assignment. Let the reader handle the >> pause (if the file split requires alignment wait). This strategy might >> work and leverage more from the framework. >> >> We probably need the following to make this work >> * extract watermark/timestamp only at the completion of a split (not at >> record level). Because records in a file aren't probably not sorted by the >> timestamp field, the pause or watermark advancement is probably better done >> at file level. >> * source readers checkpoint the watermark. otherwise, upon restart >> readers won't be able to determine the local watermark and pause for >> alignment. We don't want to emit records upon restart due to unknown >> watermark info. >> >> All, >> >> Any opinion on different timestamp for source alignment (vs Flink >> application watermark)? For Iceberg source, we might want to enforce >> alignment on kafka timestamp but Flink application watermark may use event >> time field from payload. >> >> Thanks, >> Steven >> >> On Wed, May 4, 2022 at 7:02 AM Becket Qin wrote: >> >>> Hey Piotr, >>> >>> I think the mechanism FLIP-182 provided is a reasonable default one, >>> which >>> ensures the watermarks are only drifted by an upper bound. However, >>> admittedly there are also other strategies for different purposes. >>> >>> In the Iceberg case, I am not sure if a static strictly allowed watermark >>> drift is desired. The source might just want to finish reading the >>> assigned >>> splits as fast as possible. And it is OK to have a drift of "one split", >>> instead of a fixed time period. >>> >>> As another example, if there are some fast readers whose splits are >>> always >>> throttled, while the other slow readers are struggling to keep up with >>> the >>> rest of the splits, the split enumerator may decide to reassign the slow >>> splits so all the readers have something to read. This would need the >>> SplitEnumerator to be aware of the watermark progress on each reader. So >>> it >>> seems useful to expose the WatermarkAlignmentEvent information to the >>> SplitEnumerator as well. >>> >>> Thanks, >>> >>> Jiangjie (Becket) Qin >>> >>> >>> >>> On Tue, May 3, 2022 at 7:58 PM Piotr Nowojski >>> wrote: >>> >>> > Hi Steven, >>> > >>> > Isn't this redundant to FLIP-182 and FLIP-217? Can not Iceberg just >>> emit >>> > all splits and let FLIP-182/FLIP-217 handle the watermark alignment and >>> > block the splits that are too much into the future? I can see this >>> being an >>> > issue if the existence of too many blocked splits is occupying too many >>> > resources. >>> > >>> > If that's the case, indeed SourceCoordinator/SplitEnumerator would >>> have to >>> > decide on some basis how many and which splits to assign in what >>> order. But >>> > in that case I'm not sure how much you could use from FLIP-182 and >>> > FLIP-217. They seem somehow orthogonal to me, operating on different >>> > levels. FLIP-182 and FLIP-217 are working with whatever splits have >>> already >>> > been generated and assigned. You could leverage FLIP-182 and FLIP-217 >>> and >>> > take care of only the problem to limit the number of parallel active >>> > splits. And here I'm not sure if it would be worth generalising a >>> solution >>> > across different connectors. >>> > >>> > Regarding the global watermark, I made a related comment sometime ago >>> > about it
Re: Source alignment for Iceberg
Hi Steven, Ok, thanks for the clarification. I'm not sure how much could be leveraged? Maybe just re-using the watermark alignment configuration? Please correct me if I'm wrong, but I think for the sole purpose of this use case, I don't see a good motivation behind expanding our APIs. Clearly this feature can be implemented already (you did it in the Iceberg connector after all). > As another example, if there are some fast readers whose splits are always throttled, while the other slow readers > are struggling to keep up with the rest of the splits, the split enumerator may decide to reassign the slow > splits so all the readers have something to read. This would need the SplitEnumerator to be aware of the > watermark progress on each reader. So it seems useful to expose the WatermarkAlignmentEvent information to the > SplitEnumerator as well. It seems like a valid potential use case. But do we have a good enough motivation to work on it right now? Piotrek czw., 5 maj 2022 o 16:21 Steven Wu napisał(a): > Piotr, > > With FLIP-27, Iceberg source already implemented alignment by tracking > watermark and holding back split assignment when necessary. > > The purpose of this discussion is to see if Iceberg source can leverage > some of the watermark alignment work from Flink framework. > > Thanks, > Steven > > On Thu, May 5, 2022 at 1:10 AM Piotr Nowojski > wrote: > > > Ok, I see. Thanks to both of you for the explanation. > > > > Do we need changes to Apache Flink for this feature? Can it be > implemented > > in the Sources without changes in the framework? I presume source can > > access min/max watermark from the split, so as long as it also knows > > exactly which splits have finished, it would know which splits to hold > back. > > > > Best, > > Piotrek > > > > śr., 4 maj 2022 o 20:03 Steven Wu napisał(a): > > > >> Piotr, thanks a lot for your feedback. > >> > >> > I can see this being an issue if the existence of too many blocked > >> splits is occupying too many resources. > >> > >> This is not desirable. Eagerly assigning many splits to a reader can > >> defeat the benefits of pull based dynamic split assignments. Iceberg > >> readers request one split at a time upon start or completion of a split. > >> Dynamic split assignment is better for work sharing/stealing as Becket > >> mentioned. Limiting number of active splits can be handled by the > FLIP-27 > >> Iceberg source and is somewhat orthogonal to watermark alignment. > >> > >> > Can not Iceberg just emit all splits and let FLIP-182/FLIP-217 handle > >> the watermark alignment and block the splits that are too much into the > >> future? > >> > >> The enumerator just assigns the next split to the requesting reader > >> instead of holding back the split assignment. Let the reader handle the > >> pause (if the file split requires alignment wait). This strategy might > >> work and leverage more from the framework. > >> > >> We probably need the following to make this work > >> * extract watermark/timestamp only at the completion of a split (not at > >> record level). Because records in a file aren't probably not sorted by > the > >> timestamp field, the pause or watermark advancement is probably better > done > >> at file level. > >> * source readers checkpoint the watermark. otherwise, upon restart > >> readers won't be able to determine the local watermark and pause for > >> alignment. We don't want to emit records upon restart due to unknown > >> watermark info. > >> > >> All, > >> > >> Any opinion on different timestamp for source alignment (vs Flink > >> application watermark)? For Iceberg source, we might want to enforce > >> alignment on kafka timestamp but Flink application watermark may use > event > >> time field from payload. > >> > >> Thanks, > >> Steven > >> > >> On Wed, May 4, 2022 at 7:02 AM Becket Qin wrote: > >> > >>> Hey Piotr, > >>> > >>> I think the mechanism FLIP-182 provided is a reasonable default one, > >>> which > >>> ensures the watermarks are only drifted by an upper bound. However, > >>> admittedly there are also other strategies for different purposes. > >>> > >>> In the Iceberg case, I am not sure if a static strictly allowed > watermark > >>> drift is desired. The source might just want to finish reading the > >>> assigned > >>> splits as fast as possible. And it is OK to have a drift of "one > split", > >>> instead of a fixed time period. > >>> > >>> As another example, if there are some fast readers whose splits are > >>> always > >>> throttled, while the other slow readers are struggling to keep up with > >>> the > >>> rest of the splits, the split enumerator may decide to reassign the > slow > >>> splits so all the readers have something to read. This would need the > >>> SplitEnumerator to be aware of the watermark progress on each reader. > So > >>> it > >>> seems useful to expose the WatermarkAlignmentEvent information to the > >>> SplitEnumerator as well. > >>> > >>> Thanks, > >>> > >>> Jiangjie (Becket)
Re: Source alignment for Iceberg
It seems that the iceberg source benefits from performing the alignment in the enumerator and holding back the splits until they actually can be processed. That is probably true for any similar source that assigns work in smaller increments as centralizing the "ready to process" decision in the enumerator allows for further optimizations. Maybe there is an opportunity to come up with building blocks for enumerators that benefit similar sources? It's probably less compelling to sacrifice that for what appears to be limited reuse of reader functionality? Thomas On Thu, May 5, 2022 at 12:55 PM Piotr Nowojski wrote: > > Hi Steven, > > Ok, thanks for the clarification. I'm not sure how much could be leveraged? > Maybe just re-using the watermark alignment configuration? Please correct me > if I'm wrong, but I think for the sole purpose of this use case, I don't see > a good motivation behind expanding our APIs. Clearly this feature can be > implemented already (you did it in the Iceberg connector after all). > > > As another example, if there are some fast readers whose splits are always > > throttled, while the other slow readers > > are struggling to keep up with the rest of the splits, the split enumerator > > may decide to reassign the slow > > splits so all the readers have something to read. This would need the > > SplitEnumerator to be aware of the > > watermark progress on each reader. So it seems useful to expose the > > WatermarkAlignmentEvent information to the > > SplitEnumerator as well. > > It seems like a valid potential use case. But do we have a good enough > motivation to work on it right now? > > Piotrek > > czw., 5 maj 2022 o 16:21 Steven Wu napisał(a): >> >> Piotr, >> >> With FLIP-27, Iceberg source already implemented alignment by tracking >> watermark and holding back split assignment when necessary. >> >> The purpose of this discussion is to see if Iceberg source can leverage >> some of the watermark alignment work from Flink framework. >> >> Thanks, >> Steven >> >> On Thu, May 5, 2022 at 1:10 AM Piotr Nowojski wrote: >> >> > Ok, I see. Thanks to both of you for the explanation. >> > >> > Do we need changes to Apache Flink for this feature? Can it be implemented >> > in the Sources without changes in the framework? I presume source can >> > access min/max watermark from the split, so as long as it also knows >> > exactly which splits have finished, it would know which splits to hold >> > back. >> > >> > Best, >> > Piotrek >> > >> > śr., 4 maj 2022 o 20:03 Steven Wu napisał(a): >> > >> >> Piotr, thanks a lot for your feedback. >> >> >> >> > I can see this being an issue if the existence of too many blocked >> >> splits is occupying too many resources. >> >> >> >> This is not desirable. Eagerly assigning many splits to a reader can >> >> defeat the benefits of pull based dynamic split assignments. Iceberg >> >> readers request one split at a time upon start or completion of a split. >> >> Dynamic split assignment is better for work sharing/stealing as Becket >> >> mentioned. Limiting number of active splits can be handled by the FLIP-27 >> >> Iceberg source and is somewhat orthogonal to watermark alignment. >> >> >> >> > Can not Iceberg just emit all splits and let FLIP-182/FLIP-217 handle >> >> the watermark alignment and block the splits that are too much into the >> >> future? >> >> >> >> The enumerator just assigns the next split to the requesting reader >> >> instead of holding back the split assignment. Let the reader handle the >> >> pause (if the file split requires alignment wait). This strategy might >> >> work and leverage more from the framework. >> >> >> >> We probably need the following to make this work >> >> * extract watermark/timestamp only at the completion of a split (not at >> >> record level). Because records in a file aren't probably not sorted by the >> >> timestamp field, the pause or watermark advancement is probably better >> >> done >> >> at file level. >> >> * source readers checkpoint the watermark. otherwise, upon restart >> >> readers won't be able to determine the local watermark and pause for >> >> alignment. We don't want to emit records upon restart due to unknown >> >> watermark info. >> >> >> >> All, >> >> >> >> Any opinion on different timestamp for source alignment (vs Flink >> >> application watermark)? For Iceberg source, we might want to enforce >> >> alignment on kafka timestamp but Flink application watermark may use event >> >> time field from payload. >> >> >> >> Thanks, >> >> Steven >> >> >> >> On Wed, May 4, 2022 at 7:02 AM Becket Qin wrote: >> >> >> >>> Hey Piotr, >> >>> >> >>> I think the mechanism FLIP-182 provided is a reasonable default one, >> >>> which >> >>> ensures the watermarks are only drifted by an upper bound. However, >> >>> admittedly there are also other strategies for different purposes. >> >>> >> >>> In the Iceberg case, I am not sure if a static strictly allowed watermark >> >>> drift is desired. The s
Re: Source alignment for Iceberg
On Wed, May 4, 2022 at 11:03 AM Steven Wu wrote: > Any opinion on different timestamp for source alignment (vs Flink application > watermark)? For Iceberg source, we might want to enforce alignment on kafka > timestamp but Flink application watermark may use event time field from > payload. I imagine that more generally the question is alignment based on the iceberg partition/file metadata vs. individual rows? I think that should work as long as there is a guarantee for out of orderness within the split? Thomas > > Thanks, > Steven > > On Wed, May 4, 2022 at 7:02 AM Becket Qin wrote: >> >> Hey Piotr, >> >> I think the mechanism FLIP-182 provided is a reasonable default one, which >> ensures the watermarks are only drifted by an upper bound. However, >> admittedly there are also other strategies for different purposes. >> >> In the Iceberg case, I am not sure if a static strictly allowed watermark >> drift is desired. The source might just want to finish reading the assigned >> splits as fast as possible. And it is OK to have a drift of "one split", >> instead of a fixed time period. >> >> As another example, if there are some fast readers whose splits are always >> throttled, while the other slow readers are struggling to keep up with the >> rest of the splits, the split enumerator may decide to reassign the slow >> splits so all the readers have something to read. This would need the >> SplitEnumerator to be aware of the watermark progress on each reader. So it >> seems useful to expose the WatermarkAlignmentEvent information to the >> SplitEnumerator as well. >> >> Thanks, >> >> Jiangjie (Becket) Qin >> >> >> >> On Tue, May 3, 2022 at 7:58 PM Piotr Nowojski wrote: >> >> > Hi Steven, >> > >> > Isn't this redundant to FLIP-182 and FLIP-217? Can not Iceberg just emit >> > all splits and let FLIP-182/FLIP-217 handle the watermark alignment and >> > block the splits that are too much into the future? I can see this being an >> > issue if the existence of too many blocked splits is occupying too many >> > resources. >> > >> > If that's the case, indeed SourceCoordinator/SplitEnumerator would have to >> > decide on some basis how many and which splits to assign in what order. But >> > in that case I'm not sure how much you could use from FLIP-182 and >> > FLIP-217. They seem somehow orthogonal to me, operating on different >> > levels. FLIP-182 and FLIP-217 are working with whatever splits have already >> > been generated and assigned. You could leverage FLIP-182 and FLIP-217 and >> > take care of only the problem to limit the number of parallel active >> > splits. And here I'm not sure if it would be worth generalising a solution >> > across different connectors. >> > >> > Regarding the global watermark, I made a related comment sometime ago >> > about it [1]. It sounds to me like you also need to solve this problem, >> > otherwise Iceberg users will encounter late records in case of some race >> > conditions between assigning new splits and completions of older. >> > >> > Best, >> > Piotrek >> > >> > [1] >> > https://issues.apache.org/jira/browse/FLINK-21871?focusedCommentId=17495545&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-17495545 >> > >> > pon., 2 maj 2022 o 04:26 Steven Wu napisał(a): >> > >> >> add dev@ group to the thread as Thomas suggested >> >> >> >> Arvid, >> >> >> >> The scenario 3 (Dynamic assignment + temporary no split) in the FLIP-180 >> >> (idleness) can happen to Iceberg source alignment, as readers can be >> >> temporarily starved due to the holdback by the enumerator when assigning >> >> new splits upon request. >> >> >> >> Totally agree that we should decouple this discussion with the FLIP-217, >> >> which addresses the split level watermark alignment problem as a follow-up >> >> of FLIP-182 >> >> >> >> Becket, >> >> >> >> Yes, currently Iceberg source implemented the alignment leveraging the >> >> dynamic split assignment from FLIP-27 design. Basically, the enumerator >> >> can >> >> hold back split assignments to readers when necessary. Everything are >> >> centralized in the enumerator: (1) watermark extraction and aggregation >> >> (2) >> >> alignment decision and execution >> >> >> >> The motivation of this discussion is to see if Iceberg source can leverage >> >> some of the watermark alignment solutions (like FLIP-182) from Flink >> >> framework. E.g., as mentioned in the doc, Iceberg source can potentially >> >> leverage the FLIP-182 framework to do the watermark extraction and >> >> aggregation. For the alignment decision and execution, we can keep them in >> >> the centralized enumerator. >> >> >> >> Thanks, >> >> Steven >> >> >> >> On Thu, Apr 28, 2022 at 2:05 AM Becket Qin wrote: >> >> >> >> > Hi Steven, >> >> > >> >> > Thanks for pulling me into this thread. I think the timestamp >> >> > alignment use case here is a good example of what FLIP-27 was designed >> >> for. >> >> > >> >> > Technically speaking, Iceberg source can alr
Re: Source alignment for Iceberg
I think the key point here is essentially what information should Flink expose to the user pluggables. Apparently split / local task watermark is something many user pluggables would be interested in. Right now it is calculated by the Flink framework but not exposed to the users space, i.e. SourceReader / SplitEnumerator. So it looks at least we can offer this information in some way so users can leverage that information to do things. That said, I am not sure if this would help in the Iceberg alignment case. Because at this point, FLIP-182 reports source reader watermarks periodically, which may not align with the RequestSplitEvent. So if we really want to leverage the FLIP-182 mechanism here, I see a few ways, just to name two of them: 1. we can expose the source reader watermark in the SourceReaderContext, so the source readers can put the local watermark in a custom operator event. This will effectively bypass the existing RequestSplitEvent. Or we can also extend the RequestSplitEvent to add an additional info field of byte[] type, so users can piggy-back additional information there, be it watermark or other stuff. 2. Simply piggy-back the local watermark in the RequestSplitEvent and pass that info to the SplitEnumerator as well. If we are going to do this, personally I'd prefer the first way, as it provides a mechanism to allow future extension. So it would be easier to expose other framework information to the user space in the future. Thanks, Jiangjie (Becket) Qin On Fri, May 6, 2022 at 6:15 AM Thomas Weise wrote: > On Wed, May 4, 2022 at 11:03 AM Steven Wu wrote: > > Any opinion on different timestamp for source alignment (vs Flink > application watermark)? For Iceberg source, we might want to enforce > alignment on kafka timestamp but Flink application watermark may use event > time field from payload. > > I imagine that more generally the question is alignment based on the > iceberg partition/file metadata vs. individual rows? I think that > should work as long as there is a guarantee for out of orderness > within the split? > > Thomas > > > > > Thanks, > > Steven > > > > On Wed, May 4, 2022 at 7:02 AM Becket Qin wrote: > >> > >> Hey Piotr, > >> > >> I think the mechanism FLIP-182 provided is a reasonable default one, > which > >> ensures the watermarks are only drifted by an upper bound. However, > >> admittedly there are also other strategies for different purposes. > >> > >> In the Iceberg case, I am not sure if a static strictly allowed > watermark > >> drift is desired. The source might just want to finish reading the > assigned > >> splits as fast as possible. And it is OK to have a drift of "one split", > >> instead of a fixed time period. > >> > >> As another example, if there are some fast readers whose splits are > always > >> throttled, while the other slow readers are struggling to keep up with > the > >> rest of the splits, the split enumerator may decide to reassign the slow > >> splits so all the readers have something to read. This would need the > >> SplitEnumerator to be aware of the watermark progress on each reader. > So it > >> seems useful to expose the WatermarkAlignmentEvent information to the > >> SplitEnumerator as well. > >> > >> Thanks, > >> > >> Jiangjie (Becket) Qin > >> > >> > >> > >> On Tue, May 3, 2022 at 7:58 PM Piotr Nowojski > wrote: > >> > >> > Hi Steven, > >> > > >> > Isn't this redundant to FLIP-182 and FLIP-217? Can not Iceberg just > emit > >> > all splits and let FLIP-182/FLIP-217 handle the watermark alignment > and > >> > block the splits that are too much into the future? I can see this > being an > >> > issue if the existence of too many blocked splits is occupying too > many > >> > resources. > >> > > >> > If that's the case, indeed SourceCoordinator/SplitEnumerator would > have to > >> > decide on some basis how many and which splits to assign in what > order. But > >> > in that case I'm not sure how much you could use from FLIP-182 and > >> > FLIP-217. They seem somehow orthogonal to me, operating on different > >> > levels. FLIP-182 and FLIP-217 are working with whatever splits have > already > >> > been generated and assigned. You could leverage FLIP-182 and FLIP-217 > and > >> > take care of only the problem to limit the number of parallel active > >> > splits. And here I'm not sure if it would be worth generalising a > solution > >> > across different connectors. > >> > > >> > Regarding the global watermark, I made a related comment sometime ago > >> > about it [1]. It sounds to me like you also need to solve this > problem, > >> > otherwise Iceberg users will encounter late records in case of some > race > >> > conditions between assigning new splits and completions of older. > >> > > >> > Best, > >> > Piotrek > >> > > >> > [1] > >> > > https://issues.apache.org/jira/browse/FLINK-21871?focusedCommentId=17495545&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-17495545 > >> > > >> > pon., 2 maj 2022 o
Re: Source alignment for Iceberg
Option 1 sounds reasonable but I would be tempted to wait for a second motivational use case before generalizing the framework. However I wouldn’t oppose this extension if others feel it’s useful and good thing to do Piotrek > Wiadomość napisana przez Becket Qin w dniu 06.05.2022, > o godz. 03:50: > > I think the key point here is essentially what information should Flink > expose to the user pluggables. Apparently split / local task watermark is > something many user pluggables would be interested in. Right now it is > calculated by the Flink framework but not exposed to the users space, i.e. > SourceReader / SplitEnumerator. So it looks at least we can offer this > information in some way so users can leverage that information to do > things. > > That said, I am not sure if this would help in the Iceberg alignment case. > Because at this point, FLIP-182 reports source reader watermarks > periodically, which may not align with the RequestSplitEvent. So if we > really want to leverage the FLIP-182 mechanism here, I see a few ways, just > to name two of them: > 1. we can expose the source reader watermark in the SourceReaderContext, so > the source readers can put the local watermark in a custom operator event. > This will effectively bypass the existing RequestSplitEvent. Or we can also > extend the RequestSplitEvent to add an additional info field of byte[] > type, so users can piggy-back additional information there, be it watermark > or other stuff. > 2. Simply piggy-back the local watermark in the RequestSplitEvent and pass > that info to the SplitEnumerator as well. > > If we are going to do this, personally I'd prefer the first way, as it > provides a mechanism to allow future extension. So it would be easier to > expose other framework information to the user space in the future. > > Thanks, > > Jiangjie (Becket) Qin > > > >> On Fri, May 6, 2022 at 6:15 AM Thomas Weise wrote: >> >>> On Wed, May 4, 2022 at 11:03 AM Steven Wu wrote: >>> Any opinion on different timestamp for source alignment (vs Flink >> application watermark)? For Iceberg source, we might want to enforce >> alignment on kafka timestamp but Flink application watermark may use event >> time field from payload. >> >> I imagine that more generally the question is alignment based on the >> iceberg partition/file metadata vs. individual rows? I think that >> should work as long as there is a guarantee for out of orderness >> within the split? >> >> Thomas >> >>> >>> Thanks, >>> Steven >>> >>> On Wed, May 4, 2022 at 7:02 AM Becket Qin wrote: Hey Piotr, I think the mechanism FLIP-182 provided is a reasonable default one, >> which ensures the watermarks are only drifted by an upper bound. However, admittedly there are also other strategies for different purposes. In the Iceberg case, I am not sure if a static strictly allowed >> watermark drift is desired. The source might just want to finish reading the >> assigned splits as fast as possible. And it is OK to have a drift of "one split", instead of a fixed time period. As another example, if there are some fast readers whose splits are >> always throttled, while the other slow readers are struggling to keep up with >> the rest of the splits, the split enumerator may decide to reassign the slow splits so all the readers have something to read. This would need the SplitEnumerator to be aware of the watermark progress on each reader. >> So it seems useful to expose the WatermarkAlignmentEvent information to the SplitEnumerator as well. Thanks, Jiangjie (Becket) Qin On Tue, May 3, 2022 at 7:58 PM Piotr Nowojski >> wrote: > Hi Steven, > > Isn't this redundant to FLIP-182 and FLIP-217? Can not Iceberg just >> emit > all splits and let FLIP-182/FLIP-217 handle the watermark alignment >> and > block the splits that are too much into the future? I can see this >> being an > issue if the existence of too many blocked splits is occupying too >> many > resources. > > If that's the case, indeed SourceCoordinator/SplitEnumerator would >> have to > decide on some basis how many and which splits to assign in what >> order. But > in that case I'm not sure how much you could use from FLIP-182 and > FLIP-217. They seem somehow orthogonal to me, operating on different > levels. FLIP-182 and FLIP-217 are working with whatever splits have >> already > been generated and assigned. You could leverage FLIP-182 and FLIP-217 >> and > take care of only the problem to limit the number of parallel active > splits. And here I'm not sure if it would be worth generalising a >> solution > across different connectors. > > Regarding the global watermark, I made a related comment sometime ago > about it [1]. It sounds to me like you also need to solve this >> problem, > o
Re: Source alignment for Iceberg
The conclusion of this discussion could be that we don't see much value in leveraging FLIP-182 with Iceberg source. That would totally be fine. For me, one big sticking point is the alignment timestamp for the (Iceberg) source might be the same as the Flink application watermark. On Thu, May 5, 2022 at 9:53 PM Piotr Nowojski wrote: > Option 1 sounds reasonable but I would be tempted to wait for a second > motivational use case before generalizing the framework. However I wouldn’t > oppose this extension if others feel it’s useful and good thing to do > > Piotrek > > > Wiadomość napisana przez Becket Qin w dniu > 06.05.2022, o godz. 03:50: > > > > I think the key point here is essentially what information should Flink > > expose to the user pluggables. Apparently split / local task watermark is > > something many user pluggables would be interested in. Right now it is > > calculated by the Flink framework but not exposed to the users space, > i.e. > > SourceReader / SplitEnumerator. So it looks at least we can offer this > > information in some way so users can leverage that information to do > > things. > > > > That said, I am not sure if this would help in the Iceberg alignment > case. > > Because at this point, FLIP-182 reports source reader watermarks > > periodically, which may not align with the RequestSplitEvent. So if we > > really want to leverage the FLIP-182 mechanism here, I see a few ways, > just > > to name two of them: > > 1. we can expose the source reader watermark in the SourceReaderContext, > so > > the source readers can put the local watermark in a custom operator > event. > > This will effectively bypass the existing RequestSplitEvent. Or we can > also > > extend the RequestSplitEvent to add an additional info field of byte[] > > type, so users can piggy-back additional information there, be it > watermark > > or other stuff. > > 2. Simply piggy-back the local watermark in the RequestSplitEvent and > pass > > that info to the SplitEnumerator as well. > > > > If we are going to do this, personally I'd prefer the first way, as it > > provides a mechanism to allow future extension. So it would be easier to > > expose other framework information to the user space in the future. > > > > Thanks, > > > > Jiangjie (Becket) Qin > > > > > > > >> On Fri, May 6, 2022 at 6:15 AM Thomas Weise wrote: > >> > >>> On Wed, May 4, 2022 at 11:03 AM Steven Wu > wrote: > >>> Any opinion on different timestamp for source alignment (vs Flink > >> application watermark)? For Iceberg source, we might want to enforce > >> alignment on kafka timestamp but Flink application watermark may use > event > >> time field from payload. > >> > >> I imagine that more generally the question is alignment based on the > >> iceberg partition/file metadata vs. individual rows? I think that > >> should work as long as there is a guarantee for out of orderness > >> within the split? > >> > >> Thomas > >> > >>> > >>> Thanks, > >>> Steven > >>> > >>> On Wed, May 4, 2022 at 7:02 AM Becket Qin > wrote: > > Hey Piotr, > > I think the mechanism FLIP-182 provided is a reasonable default one, > >> which > ensures the watermarks are only drifted by an upper bound. However, > admittedly there are also other strategies for different purposes. > > In the Iceberg case, I am not sure if a static strictly allowed > >> watermark > drift is desired. The source might just want to finish reading the > >> assigned > splits as fast as possible. And it is OK to have a drift of "one > split", > instead of a fixed time period. > > As another example, if there are some fast readers whose splits are > >> always > throttled, while the other slow readers are struggling to keep up with > >> the > rest of the splits, the split enumerator may decide to reassign the > slow > splits so all the readers have something to read. This would need the > SplitEnumerator to be aware of the watermark progress on each reader. > >> So it > seems useful to expose the WatermarkAlignmentEvent information to the > SplitEnumerator as well. > > Thanks, > > Jiangjie (Becket) Qin > > > > On Tue, May 3, 2022 at 7:58 PM Piotr Nowojski > >> wrote: > > > Hi Steven, > > > > Isn't this redundant to FLIP-182 and FLIP-217? Can not Iceberg just > >> emit > > all splits and let FLIP-182/FLIP-217 handle the watermark alignment > >> and > > block the splits that are too much into the future? I can see this > >> being an > > issue if the existence of too many blocked splits is occupying too > >> many > > resources. > > > > If that's the case, indeed SourceCoordinator/SplitEnumerator would > >> have to > > decide on some basis how many and which splits to assign in what > >> order. But > > in that case I'm not sure how much you could use from FLIP-182 and > > FLIP-217. They seem somehow orthogonal to m
Re: Source alignment for Iceberg
might be the same as => might NOT be the same as On Fri, May 6, 2022 at 8:13 PM Steven Wu wrote: > The conclusion of this discussion could be that we don't see much value in > leveraging FLIP-182 with Iceberg source. That would totally be fine. > > For me, one big sticking point is the alignment timestamp for the > (Iceberg) source might be the same as the Flink application watermark. > > On Thu, May 5, 2022 at 9:53 PM Piotr Nowojski > wrote: > >> Option 1 sounds reasonable but I would be tempted to wait for a second >> motivational use case before generalizing the framework. However I wouldn’t >> oppose this extension if others feel it’s useful and good thing to do >> >> Piotrek >> >> > Wiadomość napisana przez Becket Qin w dniu >> 06.05.2022, o godz. 03:50: >> > >> > I think the key point here is essentially what information should Flink >> > expose to the user pluggables. Apparently split / local task watermark >> is >> > something many user pluggables would be interested in. Right now it is >> > calculated by the Flink framework but not exposed to the users space, >> i.e. >> > SourceReader / SplitEnumerator. So it looks at least we can offer this >> > information in some way so users can leverage that information to do >> > things. >> > >> > That said, I am not sure if this would help in the Iceberg alignment >> case. >> > Because at this point, FLIP-182 reports source reader watermarks >> > periodically, which may not align with the RequestSplitEvent. So if we >> > really want to leverage the FLIP-182 mechanism here, I see a few ways, >> just >> > to name two of them: >> > 1. we can expose the source reader watermark in the >> SourceReaderContext, so >> > the source readers can put the local watermark in a custom operator >> event. >> > This will effectively bypass the existing RequestSplitEvent. Or we can >> also >> > extend the RequestSplitEvent to add an additional info field of byte[] >> > type, so users can piggy-back additional information there, be it >> watermark >> > or other stuff. >> > 2. Simply piggy-back the local watermark in the RequestSplitEvent and >> pass >> > that info to the SplitEnumerator as well. >> > >> > If we are going to do this, personally I'd prefer the first way, as it >> > provides a mechanism to allow future extension. So it would be easier to >> > expose other framework information to the user space in the future. >> > >> > Thanks, >> > >> > Jiangjie (Becket) Qin >> > >> > >> > >> >> On Fri, May 6, 2022 at 6:15 AM Thomas Weise wrote: >> >> >> >>> On Wed, May 4, 2022 at 11:03 AM Steven Wu >> wrote: >> >>> Any opinion on different timestamp for source alignment (vs Flink >> >> application watermark)? For Iceberg source, we might want to enforce >> >> alignment on kafka timestamp but Flink application watermark may use >> event >> >> time field from payload. >> >> >> >> I imagine that more generally the question is alignment based on the >> >> iceberg partition/file metadata vs. individual rows? I think that >> >> should work as long as there is a guarantee for out of orderness >> >> within the split? >> >> >> >> Thomas >> >> >> >>> >> >>> Thanks, >> >>> Steven >> >>> >> >>> On Wed, May 4, 2022 at 7:02 AM Becket Qin >> wrote: >> >> Hey Piotr, >> >> I think the mechanism FLIP-182 provided is a reasonable default one, >> >> which >> ensures the watermarks are only drifted by an upper bound. However, >> admittedly there are also other strategies for different purposes. >> >> In the Iceberg case, I am not sure if a static strictly allowed >> >> watermark >> drift is desired. The source might just want to finish reading the >> >> assigned >> splits as fast as possible. And it is OK to have a drift of "one >> split", >> instead of a fixed time period. >> >> As another example, if there are some fast readers whose splits are >> >> always >> throttled, while the other slow readers are struggling to keep up >> with >> >> the >> rest of the splits, the split enumerator may decide to reassign the >> slow >> splits so all the readers have something to read. This would need the >> SplitEnumerator to be aware of the watermark progress on each reader. >> >> So it >> seems useful to expose the WatermarkAlignmentEvent information to the >> SplitEnumerator as well. >> >> Thanks, >> >> Jiangjie (Becket) Qin >> >> >> >> On Tue, May 3, 2022 at 7:58 PM Piotr Nowojski >> >> wrote: >> >> > Hi Steven, >> > >> > Isn't this redundant to FLIP-182 and FLIP-217? Can not Iceberg just >> >> emit >> > all splits and let FLIP-182/FLIP-217 handle the watermark alignment >> >> and >> > block the splits that are too much into the future? I can see this >> >> being an >> > issue if the existence of too many blocked splits is occupying too >> >> many >> > resources. >> > >> > If that's the case, indeed SourceCoordinator/SplitEn
Re: Source alignment for Iceberg
Hey Steven, Your conclusion at this point sounds reasonable to me. That being said, I think we need to consider a bit more about the extensibility of Flink in the future. I would be happy to drive some efforts in that direction. So later on, the timestamp alignment of Iceberg may be able to leverage some of the capabilities in the framework. Thanks again for the detailed discussion! Cheers, Jiangjie (Becket) Qin On Sat, May 7, 2022 at 11:15 AM Steven Wu wrote: > might be the same as => might NOT be the same as > > On Fri, May 6, 2022 at 8:13 PM Steven Wu wrote: > > > The conclusion of this discussion could be that we don't see much value > in > > leveraging FLIP-182 with Iceberg source. That would totally be fine. > > > > For me, one big sticking point is the alignment timestamp for the > > (Iceberg) source might be the same as the Flink application watermark. > > > > On Thu, May 5, 2022 at 9:53 PM Piotr Nowojski > > wrote: > > > >> Option 1 sounds reasonable but I would be tempted to wait for a second > >> motivational use case before generalizing the framework. However I > wouldn’t > >> oppose this extension if others feel it’s useful and good thing to do > >> > >> Piotrek > >> > >> > Wiadomość napisana przez Becket Qin w dniu > >> 06.05.2022, o godz. 03:50: > >> > > >> > I think the key point here is essentially what information should > Flink > >> > expose to the user pluggables. Apparently split / local task watermark > >> is > >> > something many user pluggables would be interested in. Right now it is > >> > calculated by the Flink framework but not exposed to the users space, > >> i.e. > >> > SourceReader / SplitEnumerator. So it looks at least we can offer this > >> > information in some way so users can leverage that information to do > >> > things. > >> > > >> > That said, I am not sure if this would help in the Iceberg alignment > >> case. > >> > Because at this point, FLIP-182 reports source reader watermarks > >> > periodically, which may not align with the RequestSplitEvent. So if we > >> > really want to leverage the FLIP-182 mechanism here, I see a few ways, > >> just > >> > to name two of them: > >> > 1. we can expose the source reader watermark in the > >> SourceReaderContext, so > >> > the source readers can put the local watermark in a custom operator > >> event. > >> > This will effectively bypass the existing RequestSplitEvent. Or we can > >> also > >> > extend the RequestSplitEvent to add an additional info field of byte[] > >> > type, so users can piggy-back additional information there, be it > >> watermark > >> > or other stuff. > >> > 2. Simply piggy-back the local watermark in the RequestSplitEvent and > >> pass > >> > that info to the SplitEnumerator as well. > >> > > >> > If we are going to do this, personally I'd prefer the first way, as it > >> > provides a mechanism to allow future extension. So it would be easier > to > >> > expose other framework information to the user space in the future. > >> > > >> > Thanks, > >> > > >> > Jiangjie (Becket) Qin > >> > > >> > > >> > > >> >> On Fri, May 6, 2022 at 6:15 AM Thomas Weise wrote: > >> >> > >> >>> On Wed, May 4, 2022 at 11:03 AM Steven Wu > >> wrote: > >> >>> Any opinion on different timestamp for source alignment (vs Flink > >> >> application watermark)? For Iceberg source, we might want to enforce > >> >> alignment on kafka timestamp but Flink application watermark may use > >> event > >> >> time field from payload. > >> >> > >> >> I imagine that more generally the question is alignment based on the > >> >> iceberg partition/file metadata vs. individual rows? I think that > >> >> should work as long as there is a guarantee for out of orderness > >> >> within the split? > >> >> > >> >> Thomas > >> >> > >> >>> > >> >>> Thanks, > >> >>> Steven > >> >>> > >> >>> On Wed, May 4, 2022 at 7:02 AM Becket Qin > >> wrote: > >> > >> Hey Piotr, > >> > >> I think the mechanism FLIP-182 provided is a reasonable default > one, > >> >> which > >> ensures the watermarks are only drifted by an upper bound. However, > >> admittedly there are also other strategies for different purposes. > >> > >> In the Iceberg case, I am not sure if a static strictly allowed > >> >> watermark > >> drift is desired. The source might just want to finish reading the > >> >> assigned > >> splits as fast as possible. And it is OK to have a drift of "one > >> split", > >> instead of a fixed time period. > >> > >> As another example, if there are some fast readers whose splits are > >> >> always > >> throttled, while the other slow readers are struggling to keep up > >> with > >> >> the > >> rest of the splits, the split enumerator may decide to reassign the > >> slow > >> splits so all the readers have something to read. This would need > the > >> SplitEnumerator to be aware of the watermark progress on each > reader. > >> >> So it > >> seems useful to expose the
