On Tue, Aug 4, 2020 at 1:08 PM jmac...@godaddy.com <jmac...@godaddy.com>
wrote:

> So, after some additional digging, it appears that Beam does not
> consistently check for timer expiry before calling process. The result is
> that it may be the case that the watermark has moved beyond your timer
> expiry, and if youre counting on the timer callback happening at the time
> you set it for, that simply may NOT have happened when you are in
> DoFn.process(). You can “fix” the behavior by simply checking the watermark
> manually in process() and doing what you would normally do for timestamp
> exipry before proceeding. See my latest updated code reproducing the issue
> and showing the fix at  https://github.com/randomsamples/pardo_repro.
>
>
>
> I would argue that users of this API will naturally expect that timer
> callback semantics will guarantee that when they are in process(), if the
> current watermark is past a timers expiry that the timer callback in
> question will have been called. Is there any reason why this isn’t
> happening? Am I misunderstanding something?
>

Timers do not expire synchronously with the watermark advancing. So if you
have a timer set for 12pm and the watermark advances past 12pm, that timer
is now eligible to fire, but might not fire immediately. Some other
elements may process before that timer fires.

There are multiple reasons for this, but one is that Beam does not
guarantee that watermark advancement is synchronous with element
processing. The watermark might advance suddenly while in the middle
processing an element, or at any other time. This makes it impossible (or
at least, exceedingly difficult) to really provide the guarantee you
expected.

Reuven

>
>
> *From: *"jmac...@godaddy.com" <jmac...@godaddy.com>
> *Reply-To: *"dev@beam.apache.org" <dev@beam.apache.org>
> *Date: *Monday, August 3, 2020 at 10:51 AM
> *To: *"dev@beam.apache.org" <dev@beam.apache.org>
> *Subject: *Re: Stateful Pardo Question
>
>
>
> Notice: This email is from an external sender.
>
>
>
> Yeah, unless I am misunderstanding something. The output from my repro
> code shows event timestamp and the context timestamp every time we process
> an event.
>
> Receiving event at: 2000-01-01T00:00:00.000Z
>
> Resetting timer to : 2000-01-01T00:15:00.000Z
>
> Receiving event at: 2000-01-01T00:05:00.000Z
>
> Resetting timer to : 2000-01-01T00:20:00.000Z ß Shouldn’t the timer have
> fired before we processed the next event?
>
> Receiving event at: 2000-01-01T00:40:00.000Z
>
> Why didnt the timer fire?
>
> Resetting timer to : 2000-01-01T00:55:00.000Z
>
> Receiving event at: 2000-01-01T00:45:00.000Z
>
> Resetting timer to : 2000-01-01T01:00:00.000Z
>
> Receiving event at: 2000-01-01T00:50:00.000Z
>
> Resetting timer to : 2000-01-01T01:05:00.000Z
>
> Timer firing at: 2000-01-01T01:05:00.000Z
>
>
>
> *From: *Reuven Lax <re...@google.com>
> *Reply-To: *"dev@beam.apache.org" <dev@beam.apache.org>
> *Date: *Monday, August 3, 2020 at 10:02 AM
> *To: *dev <dev@beam.apache.org>
> *Subject: *Re: Stateful Pardo Question
>
>
>
> Notice: This email is from an external sender.
>
>
>
> Are you sure that there is a 15 minute gap in your data?
>
>
>
> On Mon, Aug 3, 2020 at 6:20 AM jmac...@godaddy.com <jmac...@godaddy.com>
> wrote:
>
> I am confused about the behavior of timers on a simple stateful pardo. I
> have put together a little repro here:
> https://github.com/randomsamples/pardo_repro
>
>
>
> I basically want to build something like a session window, accumulating
> events until quiescence of the stream for a given key and gap time, then
> output results. But it appears that the timer is not firing when the
> watermark is passed it expiration time, so the event stream is not being
> split as I would have expected. Would love some help getting this work, the
> behavior is for a project I’m working on.
>
>

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