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
