Hi All, Thanks for the answers!
Unless there are some objections or suggestions, I will open a voting thread later this week. > My original thought was to show how much time a sampled record is processed > within each operator in stream processing. By saying 'sampled', I mean we > won't generate a trace for every record due to the high cost involved. > Instead, we could only trace ONE record from source when the user requests > it (via REST API or Web UI) or when triggered periodically at a very low > frequency. That would be useful, but another issue is that we can not measure time reliably at the granularity of a single record. Time to process a single record by the whole operator chain is usually faster compared to the syscalls to measure time. So I think we are stuck with sample based profilers, like Flame Graphs generated by the Flink WebUI. Best, Piotrek czw., 9 lis 2023 o 05:32 Rui Fan <1996fan...@gmail.com> napisał(a): > Hi Piotr: > > Thanks for your reply! > > > About structured logging (basically events?) I vaguely remember some > > discussions about that. It might be a much larger topic, so I would > prefer > > to leave it out of the scope of this FLIP. > > Sounds make sense to me! > > > I think those could be indeed useful. If you would like to contribute to > them > > in the future, I would be happy to review the FLIP for it :) > > Thank you, after this FLIP, I or my colleagues can pick it up! > > Best, > Rui > > On Thu, Nov 9, 2023 at 11:39 AM Zakelly Lan <zakelly....@gmail.com> wrote: > > > Hi Piotr, > > > > Thanks for your detailed explanation! I could see the challenge of > > implementing traces with multiple spans and agree to put it in the future > > work. I personally prefer the idea of generating multi span traces for > > checkpoints on the JM only. > > > > > I'm not sure if I understand the proposal - I don't know how traces > could > > > be used for this purpose? > > > Traces are perfect for one of events (like checkpointing, recovery, > etc), > > > not for continuous monitoring > > > (like processing records). That's what metrics are. Creating trace and > > > span(s) per each record would > > > be prohibitively expensive. > > > > My original thought was to show how much time a sampled record is > processed > > within each operator in stream processing. By saying 'sampled', I mean we > > won't generate a trace for every record due to the high cost involved. > > Instead, we could only trace ONE record from source when the user > requests > > it (via REST API or Web UI) or when triggered periodically at a very low > > frequency. However after re-thinking my idea, I realized it's hard to > > define the whole lifecycle of a record since it is transformed into > > different forms among operators. We could discuss this in future after > the > > basic trace is implemented in Flink. > > > > > Unless you mean in batch/bounded jobs? Then yes, we could create a > > bounded > > > job trace, with spans > > > for every stage/task/subtask. > > > > Oh yes, batch jobs could definitely leverage the trace. > > > > Best, > > Zakelly > > > > > > On Wed, Nov 8, 2023 at 9:18 PM Jinzhong Li <lijinzhong2...@gmail.com> > > wrote: > > > > > Hi Piotr, > > > > > > Thanks for driving this proposal! I strongly agree that the existing > > > metric APIs are not suitable for monitoring restore/checkpoint > behavior! > > > > > > I think the TM-level recovery/checkpointing traces are necessary in the > > > future. In our production environment, we sometimes encounter that job > > > recovery time is very long (30min+), due to several subTask heavy disk > > > traffic. The TM-level recovery trace is helpful for troubleshooting > such > > > issues. > > > > > > Best > > > Jinzhong > > > > > > On Wed, Nov 8, 2023 at 5:09 PM Piotr Nowojski <pnowoj...@apache.org> > > > wrote: > > > > > > > Hi Zakelly, > > > > > > > > Thanks for the comments. Quick answer for both of your questions > would > > be > > > > that it probably should be > > > > left as a future work. For more detailed answers please take a look > > below > > > > :) > > > > > > > > > Does it mean the inclusion and subdivision relationships of spans > > > defined > > > > > by "parent_id" are not supported? I think it is a very necessary > > > feature > > > > > for the trace. > > > > > > > > Yes exactly, that is the current limitation. This could be solved > > somehow > > > > one way or another in the future. > > > > > > > > Support for reporting multi span traces all at once - for example > > > > `CheckpointStatsTracker` running JM, > > > > could upon checkpoint completion create in one place the whole > > structure > > > of > > > > parent spans, to have for > > > > example one span per each subtask. This would be a relatively easy > > follow > > > > up. > > > > > > > > However, if we would like to create true distributed traces, with > spans > > > > reported from many different > > > > components, potentially both on JM and TM, the problem is a bit > deeper. > > > The > > > > issue in that case is how > > > > to actually fill out `parrent_id` and `trace_id`? Passing some > context > > > > entity as a java object would be > > > > unfeasible. That would require too many changes in too many places. I > > > think > > > > the only realistic way > > > > to do it, would be to have a deterministic generator of `parten_id` > and > > > > `trace_id` values. > > > > > > > > For example we could create the parent trace/span of the checkpoint > on > > > JM, > > > > and set those ids to > > > > something like: `jobId#attemptId#checkpointId`. Each subtask then > could > > > > re-generate those ids > > > > and subtasks' checkpoint span would have an id of > > > > `jobId#attemptId#checkpointId#subTaskId`. > > > > Note that this is just an example, as most likely distributed spans > for > > > > checkpointing do not make > > > > sense, as we can generate them much easier on the JM anyway. > > > > > > > > > In addition to checkpoint and recovery, I believe the trace would > > also > > > be > > > > > valuable for performance tuning. If Flink can trace and visualize > the > > > > time > > > > > cost of each operator and stage for a sampled record, users would > be > > > able > > > > > to easily determine the end-to-end latency and identify performance > > > > issues > > > > > for optimization. Looking forward to seeing these in the future. > > > > > > > > I'm not sure if I understand the proposal - I don't know how traces > > could > > > > be used for this purpose? > > > > Traces are perfect for one of events (like checkpointing, recovery, > > etc), > > > > not for continuous monitoring > > > > (like processing records). That's what metrics are. Creating trace > and > > > > span(s) per each record would > > > > be prohibitively expensive. > > > > > > > > Unless you mean in batch/bounded jobs? Then yes, we could create a > > > bounded > > > > job trace, with spans > > > > for every stage/task/subtask. > > > > > > > > Best, > > > > Piotrek > > > > > > > > > > > > śr., 8 lis 2023 o 05:30 Zakelly Lan <zakelly....@gmail.com> > > napisał(a): > > > > > > > > > Hi Piotr, > > > > > > > > > > Happy to see the trace! Thanks for this proposal. > > > > > > > > > > One minor question: It is mentioned in the interface of Span: > > > > > > > > > > Currently we don't support traces with multiple spans. Each span is > > > > > > self-contained and represents things like a checkpoint or > recovery. > > > > > > > > > > > > > > > Does it mean the inclusion and subdivision relationships of spans > > > defined > > > > > by "parent_id" are not supported? I think it is a very necessary > > > feature > > > > > for the trace. > > > > > > > > > > In addition to checkpoint and recovery, I believe the trace would > > also > > > be > > > > > valuable for performance tuning. If Flink can trace and visualize > the > > > > time > > > > > cost of each operator and stage for a sampled record, users would > be > > > able > > > > > to easily determine the end-to-end latency and identify performance > > > > issues > > > > > for optimization. Looking forward to seeing these in the future. > > > > > > > > > > Best, > > > > > Zakelly > > > > > > > > > > > > > > > On Tue, Nov 7, 2023 at 6:27 PM Piotr Nowojski < > pnowoj...@apache.org> > > > > > wrote: > > > > > > > > > > > Hi Rui, > > > > > > > > > > > > Thanks for the comments! > > > > > > > > > > > > > 1. I see the trace just supports Span? Does it support trace > > > events? > > > > > > > I'm not sure whether tracing events is reasonable for > > > TraceReporter. > > > > > > > If it supports, flink can report checkpoint and checkpoint path > > > > > > proactively. > > > > > > > Currently, checkpoint lists or the latest checkpoint can only > be > > > > > fetched > > > > > > > by external components or platforms. And report is more timely > > and > > > > > > > efficient than fetch. > > > > > > > > > > > > No, currently the `TraceReporter` that I'm introducing supports > > only > > > > > single > > > > > > span traces. > > > > > > So currently neither events on their own, nor events inside spans > > are > > > > not > > > > > > supported. > > > > > > This is done just for the sake of simplicity, and test out the > > basic > > > > > > functionality. But I think, > > > > > > those currently missing features should be added at some point in > > > > > > the future. > > > > > > > > > > > > About structured logging (basically events?) I vaguely remember > > some > > > > > > discussions about > > > > > > that. It might be a much larger topic, so I would prefer to leave > > it > > > > out > > > > > of > > > > > > the scope of this > > > > > > FLIP. > > > > > > > > > > > > > 2. This FLIP just monitors the checkpoint and task recovery, > > right? > > > > > > > > > > > > Yes, it only adds single span traces for checkpointing and > > > > > > recovery/initialisation - one > > > > > > span per whole job per either recovery/initialization process or > > per > > > > each > > > > > > checkpoint. > > > > > > > > > > > > > Could we add more operations in this FLIP? In our production, > we > > > > > > > added a lot of trace reporters for job starts and scheduler > > > > operation. > > > > > > > They are useful if some jobs start slowly, because they will > > affect > > > > > > > the job availability. For example: > > > > > > > - From JobManager process is started to JobGraph is created > > > > > > > - From JobGraph is created to JobMaster is created > > > > > > > - From JobMaster is created to job is running > > > > > > > - From start request tm from yarn or kubernetes to all tms are > > > ready > > > > > > > - etc > > > > > > > > > > > > I think those could be indeed useful. If you would like to > > contribute > > > > > them > > > > > > in the future, > > > > > > I would be happy to review the FLIP for it :) > > > > > > > > > > > > > Of course, this FLIP doesn't include them is fine for me. The > > first > > > > > > version > > > > > > > only initializes the interface and common operations, and we > can > > > add > > > > > > > more operations in the future > > > > > > > > > > > > Yes, that's exactly my thinking :) > > > > > > > > > > > > Best, > > > > > > Piotrek > > > > > > > > > > > > wt., 7 lis 2023 o 10:05 Rui Fan <1996fan...@gmail.com> > napisał(a): > > > > > > > > > > > > > Hi Piotr, > > > > > > > > > > > > > > Thanks for driving this proposal! The trace reporter is useful > to > > > > > > > check a lot of duration monitors inside of Flink. > > > > > > > > > > > > > > I have some questions about this proposal: > > > > > > > > > > > > > > 1. I see the trace just supports Span? Does it support trace > > > events? > > > > > > > I'm not sure whether tracing events is reasonable for > > > TraceReporter. > > > > > > > If it supports, flink can report checkpoint and checkpoint path > > > > > > > proactively. > > > > > > > Currently, checkpoint lists or the latest checkpoint can only > be > > > > > fetched > > > > > > > by external components or platforms. And report is more timely > > and > > > > > > > efficient than fetch. > > > > > > > > > > > > > > 2. This FLIP just monitors the checkpoint and task recovery, > > right? > > > > > > > Could we add more operations in this FLIP? In our production, > we > > > > > > > added a lot of trace reporters for job starts and scheduler > > > > operation. > > > > > > > They are useful if some jobs start slowly, because they will > > affect > > > > > > > the job availability. For example: > > > > > > > - From JobManager process is started to JobGraph is created > > > > > > > - From JobGraph is created to JobMaster is created > > > > > > > - From JobMaster is created to job is running > > > > > > > - From start request tm from yarn or kubernetes to all tms are > > > ready > > > > > > > - etc > > > > > > > > > > > > > > Of course, this FLIP doesn't include them is fine for me. The > > first > > > > > > version > > > > > > > only initializes the interface and common operations, and we > can > > > add > > > > > > > more operations in the future. > > > > > > > > > > > > > > Best, > > > > > > > Rui > > > > > > > > > > > > > > On Tue, Nov 7, 2023 at 4:31 PM Piotr Nowojski < > > > pnowoj...@apache.org> > > > > > > > wrote: > > > > > > > > > > > > > > > Hi all! > > > > > > > > > > > > > > > > I would like to start a discussion on FLIP-384: Introduce > > > > > TraceReporter > > > > > > > and > > > > > > > > use it to create checkpointing and recovery traces [1]. > > > > > > > > > > > > > > > > This proposal intends to improve observability of Flink's > > > > > Checkpointing > > > > > > > and > > > > > > > > Recovery/Initialization operations, by adding support for > > > reporting > > > > > > > traces > > > > > > > > from Flink. In the future, reporting traces can be of course > > used > > > > for > > > > > > > other > > > > > > > > use cases and also by users. > > > > > > > > > > > > > > > > There are also two other follow up FLIPS, FLIP-385 [2] and > > > FLIP-386 > > > > > > [3], > > > > > > > > which expand the basic functionality introduced in FLIP-384 > > [1]. > > > > > > > > > > > > > > > > Please let me know what you think! > > > > > > > > > > > > > > > > Best, > > > > > > > > Piotr Nowojski > > > > > > > > > > > > > > > > [1] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-384%3A+Introduce+TraceReporter+and+use+it+to+create+checkpointing+and+recovery+traces > > > > > > > > [2] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-385%3A+Add+OpenTelemetryTraceReporter+and+OpenTelemetryMetricReporter > > > > > > > > [3] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-386%3A+Support+adding+custom+metrics+in+Recovery+Spans > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
