You are welcome :) More or less you are correct. Assigning event time doesn’t reorder anything in the stream, that’s just a meta information about a record that can be used by various functions/operators, not only by windowed operations. As I answered in “A question on the Flink "rolling" FoldFunction” topic, one could use event time for example for a "best effort" sorting mechanism (which buffers some number of elements and tries to smooth the stream out/best effort sort it), registering event time timers or for any other custom operation.
Same applies to watermarks. They are also another kind of “meta data” being passed along that can be used and is for example be the before mentioned windowed operators to emit the data/clean up the state. Piotrek > On 7 Dec 2018, at 11:19, <min....@ubs.com> <min....@ubs.com> wrote: > > Many thanks for sending your email. > > Does this mean that the event time only impacts on the event selection for a > time window? > > Without use of a time window, the event time has no impact on the order of > any records/events? > > Is my understanding correct? > > Thank you very much for your help. > > Regards, > > Min > > > > From: Piotr Nowojski [mailto:pi...@data-artisans.com] > Sent: Freitag, 7. Dezember 2018 11:11 > To: Tan, Min > Cc: user > Subject: [External] Re: Use event time > > Hi again! > > Flink doesn’t order/sort the records according to event time. The preveiling > idea is: > - records will be arriving out of order, operators should handle that > - watermarks are used for indicators of the current lower bound of the event > time “clock” > > For examples windowed joins/aggregations assign records to one or more time > windows, collect all of the data belonging to a window and when watermark > exceeds/overtakes the window that when that window is being evaluated. > > Piotrek > > > On 7 Dec 2018, at 09:22, min....@ubs.com <mailto:min....@ubs.com> wrote: > > Hi, > > I am new to Flink. > > I have the following small code to use the event time. I did not get the > result expected, i.e. it print out events in the order of event time. > > Did I miss something here? > > Regards, > > Min > > > --------------Event time------------------ > public static void main(String[] args) throws Exception { > > final StreamExecutionEnvironment env = > StreamExecutionEnvironment.getExecutionEnvironment(); > long start =System.currentTimeMillis(); > DataStream<Event> stream = env.fromElements(new Event(0,start,start), > new Event(1,start+10,start+10), new > Event(2,start+20,start-20), > new Event(3,start+30,start-30), new > Event(4,start+40,start-40)); > > stream.map(event -> "RAW order " + event.toString()).print(); > > > stream.assignTimestampsAndWatermarks(new > AscendingTimestampExtractor<Event>() { > @Override public long extractAscendingTimestamp(Event element) { > return element.time1; } }) > .map(event -> "time1 order:: " + event.toString()).print(); > > > stream.assignTimestampsAndWatermarks(new > AscendingTimestampExtractor<Event>() { > @Override public long extractAscendingTimestamp(Event element) { > return element.time2; } }) > .map(event -> "time2 order:: " + event.toString()).print(); > > env.execute("event time ........"); > } > > > static public class Event { > int id; > long time1; > long time2; > > Event(int id, long time1, long time2){ > this <http://this.id/>. <http://this.id/>id <http://this.id/> =id; > this.time1=time1; > this.time2=time2; > } > > public String toString() { > return "id=" + id + "; time1=" + time1 + "; time2=" + time2; > } > } > } > ------------------------------ > > Check out our new brand campaign: www.ubs.com/together > <http://www.ubs.com/together> > E-mails can involve SUBSTANTIAL RISKS, e.g. lack of confidentiality, > potential manipulation of contents and/or sender's address, incorrect > recipient (misdirection), viruses etc. Based on previous e-mail > correspondence with you and/or an agreement reached with you, UBS considers > itself authorized to contact you via e-mail. 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