Hi, That’s good to hear :)
I quickly went through the code and it seems reasonable. I think there might be need to think a little bit more about how this cancel checkpoint should be exposed to the operators and what should be default action - right now by default cancel flag is ignored, I would like to consider if throwing an UnsupportedOperation would be a better long therm solution. But at first glance I do not see any larger issues and it would great if you could make a pull request out of it. Piotrek > On 9 Oct 2017, at 15:56, Antoine Philippot <antoine.philip...@teads.tv> wrote: > > Thanks for your advices Piotr. > > Firstly, yes, we are aware that even with clean shutdown we can end up with > duplicated messages after a crash and it is acceptable as is it rare and > unintentional unlike deploying new business code or up/down scale. > > I made a fork of the 1.2.1 version which we currently use and developed a > simple POC based on the solution to pass a boolean stopSourceSavepoint from > the job manager to the source when a cancel with savepoint is triggered. > This is the altered code : > https://github.com/aphilippot/flink/compare/release-1.2.1...aphilippot:flink_1_2_1_POC_savepoint > > <https://github.com/aphilippot/flink/compare/release-1.2.1...aphilippot:flink_1_2_1_POC_savepoint> > > We test it with our production workload and there are no duplicated messages > any more while hundred of thousands were duplicated before. > > I planned to reapply/adapt this patch for the 1.3.2 release when we migrate > to it and maybe later to the 1.4 > > I'm open to suggestion or to help/develop this feature upstream if you want. > > > Le lun. 2 oct. 2017 à 19:09, Piotr Nowojski <pi...@data-artisans.com > <mailto:pi...@data-artisans.com>> a écrit : > We are planning to work on this clean shut down after releasing Flink 1.4. > Implementing this properly would require some work, for example: > - adding some checkpoint options to add information about “closing”/“shutting > down” event > - add clean shutdown to source functions API > - implement handling of this clean shutdown in desired sources > > Those are not super complicated changes but also not trivial. > > One thing that you could do, is to implement some super hacky filter function > just after source operator, that you would manually trigger. Normally it > would pass all of the messages. Once triggered, it would wait for next > checkpoint to happen. It would assume that it is a save point, and would > start filtering out all of the subsequent messages. When this checkpoint > completes, you could manually shutdown your Flink application. This could > guarantee that there are no duplicated writes after a restart. This might > work for clean shutdown, but it would be a very hacky solution. > > Btw, keep in mind that even with clean shutdown you can end up with > duplicated messages after a crash and there is no way around this with Kafka > 0.9. > > Piotrek > >> On Oct 2, 2017, at 5:30 PM, Antoine Philippot <antoine.philip...@teads.tv >> <mailto:antoine.philip...@teads.tv>> wrote: >> >> Thanks Piotr for your answer, we sadly can't use kafka 0.11 for now (and >> until a while). >> >> We can not afford tens of thousands of duplicated messages for each >> application upgrade, can I help by working on this feature ? >> Do you have any hint or details on this part of that "todo list" ? >> >> >> Le lun. 2 oct. 2017 à 16:50, Piotr Nowojski <pi...@data-artisans.com >> <mailto:pi...@data-artisans.com>> a écrit : >> Hi, >> >> For failures recovery with Kafka 0.9 it is not possible to avoid duplicated >> messages. Using Flink 1.4 (unreleased yet) combined with Kafka 0.11 it will >> be possible to achieve exactly-once end to end semantic when writing to >> Kafka. However this still a work in progress: >> >> https://issues.apache.org/jira/browse/FLINK-6988 >> <https://issues.apache.org/jira/browse/FLINK-6988> >> >> However this is a superset of functionality that you are asking for. >> Exactly-once just for clean shutdowns is also on our “TODO” list (it >> would/could support Kafka 0.9), but it is not currently being actively >> developed. >> >> Piotr Nowojski >> >>> On Oct 2, 2017, at 3:35 PM, Antoine Philippot <antoine.philip...@teads.tv >>> <mailto:antoine.philip...@teads.tv>> wrote: >>> >>> Hi, >>> >>> I'm working on a flink streaming app with a kafka09 to kafka09 use case >>> which handles around 100k messages per seconds. >>> >>> To upgrade our application we used to run a flink cancel with savepoint >>> command followed by a flink run with the previous saved savepoint and the >>> new application fat jar as parameter. We notice that we can have more than >>> 50k of duplicated messages in the kafka sink wich is not idempotent. >>> >>> This behaviour is actually problematic for this project and I try to find a >>> solution / workaround to avoid these duplicated messages. >>> >>> The JobManager indicates clearly that the cancel call is triggered once the >>> savepoint is finished, but during the savepoint execution, kafka source >>> continue to poll new messages which will not be part of the savepoint and >>> will be replayed on the next application start. >>> >>> I try to find a solution with the stop command line argument but the kafka >>> source doesn't implement StoppableFunction >>> (https://issues.apache.org/jira/browse/FLINK-3404 >>> <https://issues.apache.org/jira/browse/FLINK-3404>) and the savepoint >>> generation is not available with stop in contrary to cancel. >>> >>> Is there an other solution to not process duplicated messages for each >>> application upgrade or rescaling ? >>> >>> If no, has someone planned to implement it? Otherwise, I can propose a pull >>> request after some architecture advices. >>> >>> The final goal is to stop polling source and trigger a savepoint once >>> polling stopped. >>> >>> Thanks >> >
