Re: Window Functions and Empty Panes

[Kostas Kloudas]

I forgot to say that timers are fault-tolerant. You set them, and Flink takes 
care of checkpointing and
restoring them after failure. The flag will also be fault-tolerant as, i 
suppose, you will use Flink’s keyed state.

For more info, you can check the ProcessFunction documentation that Konstantin 
provided.
There, the example uses a value state to hold the counter, you can do sth 
similar to keep the flag.
Keep in mind that the state will already be scoped by key so you do not have to 
worry about that
either.

Kostas

> On Apr 18, 2017, at 11:11 PM, Kostas Kloudas  
> wrote:
> 
> No problem! Glad I could help!
> 
> Kostas
> 
>> On Apr 18, 2017, at 11:01 PM, Ryan Conway > > wrote:
>> 
>> Hi Kostas,
>> 
>> Re restarting: I missed that ProcessFunction.OnTimerContext extends 
>> ProcessFunction.Context! Until now my thought was that OnTimerContext did 
>> not provide a means of restarting a timer.
>> 
>> Re initial timer, you're right, I'll just need to track a boolean in a state 
>> variable that notes whether or not the timer has been initialized. What I am 
>> not confident about is how to manage timer recovery after a node failure; I 
>> imagine it will make sense to not track this variable. I will do more 
>> research and cross that bridge when I get there.
>> 
>> So I think a process function will work just fine, here. Thank you again for 
>> your time, Kostas and Konstantin.
>> 
>> Ryan
>> 
>> On Tue, Apr 18, 2017 at 12:07 PM, Kostas Kloudas 
>> > wrote:
>> Hi Ryan,
>> 
>> “A periodic window like this requires the ability to start a timer without 
>> an element and to restart a timer when fired.”
>> 
>> For the second part, i.e. “to restart a timer when fired”, you can 
>> re-register the timer in the onTimer() method (set a 
>> new timer for “now + T"), so that the next one fires after T time units, 
>> where T is your period.
>> 
>> For the first part, where you set the initial timer for a window, this needs 
>> to have a first element right? If not, how
>> do you know the key for which to set the timer? Are all the keys known in 
>> advance?
>> 
>> Kostas
>> 
>> 
>> 
>>> On Apr 18, 2017, at 8:35 PM, Ryan Conway >> > wrote:
>>> 
>>> A periodic window like this requires the ability to start a timer without 
>>> an element and to restart a timer when fired.
>> 
>> 
> 

Re: Window Functions and Empty Panes

[Kostas Kloudas]

Hi Ryan,

“A periodic window like this requires the ability to start a timer without an 
element and to restart a timer when fired.”

For the second part, i.e. “to restart a timer when fired”, you can re-register 
the timer in the onTimer() method (set a 
new timer for “now + T"), so that the next one fires after T time units, where 
T is your period.

For the first part, where you set the initial timer for a window, this needs to 
have a first element right? If not, how
do you know the key for which to set the timer? Are all the keys known in 
advance?

Kostas



> On Apr 18, 2017, at 8:35 PM, Ryan Conway  
> wrote:
> 
> A periodic window like this requires the ability to start a timer without an 
> element and to restart a timer when fired.