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From Kostas Kloudas <k.klou...@data-artisans.com>
Subject Re: [DISCUSS] Removing delete*Timer from the WindowOperator.Context
Date Wed, 12 Oct 2016 16:09:29 GMT
Thanks for the feedback Konstantin!
Good to hear that.

As far as the Trigger DSL is concerned, 
it is not currently in the master but it will come soon.

Kostas

> On Oct 12, 2016, at 6:05 PM, Konstantin Knauf <konstantin.knauf@tngtech.com> wrote:
> 
> Hi all,
> 
> thank you for looping me in. Because of the memory leak we first
> experienced we have built a work-around, which did not need to delete
> timers and are still using it. So for us, I think, this would currently
> not be a problem. Nevertheless, I think, it is a strong limitation if
> custom triggers can not delete timers. I am not familiar with the new
> Trigger DSL though.
> 
> Cheers,
> 
> Konstantin
> 
> On 12.10.2016 15:38, Kostas Kloudas wrote:
>> Hi all,
>> 
>> This thread has been dormant for some time now.
>> 
>> Given that this change may affect user code, I am sending this as a 
>> reminder that the discussion is still open and to re-invite anyone who
>> may be affected to participate.
>> 
>> I would suggest to leave it open till the end of next week and then, 
>> if nobody objects, we can proceed to the change.
>> 
>> What do you think?
>> 
>> Kostas
>> 
>>> On Sep 28, 2016, at 3:21 PM, Maximilian Michels <mxm@apache.org> wrote:
>>> 
>>> What are the use cases where you actually need to delete a timer? How
>>> about we only let users delete timers which they created themselves?
>>> 
>>> I guessing most of these use cases will be obsolete with the new
>>> Trigger DSL because the trigger logic can be expressed more easily. So
>>> +1 for removing the delete methods from the context.
>>> 
>>> On Tue, Sep 27, 2016 at 3:43 PM, Kostas Kloudas
>>> <k.kloudas@data-artisans.com> wrote:
>>>> Hi all,
>>>> 
>>>> As the title of this email suggests, I am proposing to remove the  methods
>>>> deleteProcessingTimeTimer(long time) and deleteEventTimeTimer(long time)
>>>> from the WindowOperator.Context. With this change, registered timers that
>>>> have nothing to do (e.g. because their state has already been cleaned up)
>>>> will be simply ignored by the windowOperator, when their time comes.
>>>> 
>>>> The reason for the change is that by allowing custom user code, e.g. a custom
Trigger,
>>>> to delete timers we may have unpredictable behavior.
>>>> 
>>>> As an example, one can imagine the case where we have allowed_lateness =
0 and the cleanup
>>>> timer for a window collides with the end_of_window one. In this case, by
deleting the end_of_window
>>>> timer from the trigger (possibly a custom one), we end up also deleting the
cleanup one,
>>>> which in turn can lead to the window state never being garbage collected.
>>>> 
>>>> To see what can be the consequences apart from memory leaks, this can easily
lead
>>>> to wrong session windows, as a session that should have been garbage collected,
will
>>>> still be around and ready to accept new data.
>>>> 
>>>> With this change, timers that should correctly be deleted will now remain
in the queue of
>>>> pending timers, but they will do nothing, while cleanup timers will cleanup
the state of their
>>>> corresponding window.
>>>> 
>>>> Other possible solutions like keeping a separate list for cleanup timers
would complicate
>>>> the codebase and also introduce memory overheads which can be avoided using
the
>>>> solution above (i.e. just ignoring timers the have nothing to do anymore).
>>>> 
>>>> What do you think?
>>>> 
>>>> Kostas
>>>> 
>> 
>> 
> 
> -- 
> Konstantin Knauf * konstantin.knauf@tngtech.com * +49-174-3413182
> TNG Technology Consulting GmbH, Betastr. 13a, 85774 Unterföhring
> Geschäftsführer: Henrik Klagges, Christoph Stock, Dr. Robert Dahlke
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> 


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