ach works if an operator has internal state <em>only</em>. <em>Internal state</em> is everything that is stored and managed by Flink&rsquo;s state backends - for example, the windowed sums in the second operator. When a process has only internal state, there is no need to perform any additional action during pre-commit aside from updating the data in the state backends before it is checkpointed. Flink takes care of correctly committing those writes in case of checkpoint success or aborting them in case of f