The input one are ignored and *replaced* by the new one you've calculated based on incoming data and their timestamps. Any downstream windowing operations will trigger based on this newly calculated watermark.
In general, I'd say that if you don't have any special use-case that requires this (I can hardly think of any), you should ideally assign watermark at the sources (or if the source doesn't allow it, right after it). D. On Thu, Dec 2, 2021 at 5:58 PM Alexis Sarda-Espinosa < alexis.sarda-espin...@microfocus.com> wrote: > Hi David, > > > > If watermarks are ignored how do Consecutive windowed operations [1] work? > I’m just trying to understand in which scenarios I need to assign > timestamps and watermarks, or if it’s enough if I do it once near the > beginning of the DAG (assuming the source doesn’t do it). > > > > > https://nightlies.apache.org/flink/flink-docs-master/docs/dev/datastream/operators/windows/#consecutive-windowed-operations > > > > Regards, > > Alexis. > > > > *From:* David Morávek <d...@apache.org> > *Sent:* Donnerstag, 2. Dezember 2021 17:26 > *To:* Alexis Sarda-Espinosa <alexis.sarda-espin...@microfocus.com> > *Cc:* user@flink.apache.org > *Subject:* Re: Watermark behavior when connecting streams > > > > Hi Alexis, > > > > please take a look at AbstractStreamOperator [1] for details how the > watermark is calculate for TwoInputOperator. It uses pretty much the same > approach as for with the single input one (it simply takes a minimum). > > > > For watermark re-assignment, we ignore input watermark unless it's > Long.MAX_LONG (this happens on shutdown, eg. savepoint + drain). You can > see more details by looking at the TimestampsAndWatermarksOperator [2]. > > > > [1] > https://github.com/apache/flink/blob/release-1.14.0/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/AbstractStreamOperator.java#L608 > > [2] > https://github.com/apache/flink/blob/release-1.14.0/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/TimestampsAndWatermarksOperator.java#L124 > > > > Best, > > D. > > > > On Wed, Dec 1, 2021 at 9:49 AM Alexis Sarda-Espinosa < > alexis.sarda-espin...@microfocus.com> wrote: > > Hi everyone, > > > > Based on what I know, a single operator with parallelism > 1 checks the > watermarks from all its streams and uses the smallest one out of the > non-idle streams. My first question is whether watermarks are forwarded as > long as a different watermark strategy is not applied downstream? For > example, will my stream keep its watermarks even after windowing + > processing? > > > > The second question is what happens with watermarks after connecting 2 > streams, specifically these 2 possibilities: > > > > - One stream was watermarks but the other one doesn’t. > > - Both streams have watermarks. > > > > Regards, > > Alexis. > > > >
