Bytewax provides some operators and pre-built configurations for easily grouping data into buckets called windows and running code on just the values in those windows.


  1. Pick a clock and create a config for it. A clock determines the time of each element and the current time used for closing each window. E.g. use the current system time. See the docs for each subclass of ClockConfig for options.

  2. Pick a windower and create a config for it. A windower defines how to take the values and their times and bucket them into windows. E.g. have tumbling windows every 30 seconds. See the docs for each subclass of WindowConfig for options.

  3. Pick a key to route the values for the window and make sure the input to the windowing operator you choose is a 2-tuple of (key: str, value). Windows are managed independently for each key. If you need all data to be processed into the same window state, you can use a constant key like ("ALL", value) but this will reduce the parallelism possible in the dataflow. This is similar to all the other stateful operators; you can read more about the concept in State Keys.

  4. Pass both these configs to the windowing operator of your choice. The windowing operators decide what kind of logic you should apply to values within a window and what should be the output of the window. E.g. reduce_window combines all values in a window into a single output and sends that downstream.

You are allowed and encouraged to have as many different clocks and windowers as you need in a single dataflow. Just instantiate more of them and pass the ones you need for each situation to each windowing operator.


Because Bytewax can be run as a distributed system with multiple worker processes and threads all reading relevant data simultaneously, you have to specifically collect and manually sort data that you need to process in strict time order.


Bytewax’s windowing system is built on top of its recovery system (see Recovery for more info), so failure in the middle of a window will be handled as gracefully as possible.

Some clocks don’t have a single correct answer on what to do during recovery. E.g. if you use SystemClockConfig with 10 minute windows, but then recover on a 15 minute mark, the system will immediately close out the half-completed window stored during recovery. See the docs for each ClockConfig subclass for specific notes on recovery.

Recovery happens on the granularity of the epochs of the dataflow, not the windows. Epoch interval has no affect on windowing operator behavior when there are no failures; it is solely an implementation detail of the recovery system. See for more information on epochs.

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