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?


> On Sep 28, 2016, at 3:21 PM, Maximilian Michels <m...@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.klou...@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

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