You might also want to change the parallelism if the rate of your input streams varies, e.g., you scale an application down over night or the weekend.
2018-02-13 13:43 GMT+01:00 Xingcan Cui <xingc...@gmail.com>: > Hi Max, > > Currently, the timers can only be used with keyed streams. As @Fabian > suggested, you can “forge” a keyed stream with the special KeySelector, > which maps all the records to the same key. > > IMO, Flink uses keyed streams/states as it’s a deterministic distribution > mechanism. Here, “the parallelism changes” may also refer to a parallelism > change after the job restarts (e.g., when a node crashes). Flink can make > sure that all the processing tasks and states will be safely re-distributed > across the new cluster. > > Hope that helps. > > Best, > Xingcan > > > On 13 Feb 2018, at 5:18 PM, m@xi <makisnt...@gmail.com> wrote: > > > > OK Great! > > > > Thanks a lot for the super ultra fast answer Fabian! > > > > One intuitive follow-up question. > > > > So, keyed state is the most preferable one, as it is easy for the Flink > > System to perform the re-distribution in case of change in parallelism, > if > > we have a scale-up or scale-down. Also, it is useful to use hash > partition a > > stream to different nodes/processors/PU (Processing Units) in general, by > > Keyed State. > > > > Any other reasons for making Keyed State a must? > > > > Last but not least, can you elaborate further on the "when the > parallelism > > changes" part. I have read this in many topics in this forum, but I > cannot > > understand its essence. For example, I define the parallelism of each > > operator in my Flink Job program based on the number of available PU. > Maybe > > the essence lies in the fast that the number of PU might change from > time to > > time, e.g. add more servers to the cluster where Flink runs and without > > stopping the Flink Job that runs you may perform the rescaling. > > > > Thanks in advance. > > > > Best, > > Max > > > > > > -- > > Sent from: http://apache-flink-user-mailing-list-archive.2336050. > n4.nabble.com/ > > > >