 we best
store fault-tolerant window state within the <code>KeyedProcessFunction</code>. One
approach would be to create and manage separate <code>MapStates</code> per rule. Such
an approach, however, would be wasteful - we would separately hold state
for overlapping time windows, and therefore unnecessarily store
duplicate events. A better approach is to always store just enough data
to be able to estimate all currently active rules which are scoped by
the same key. In order to achieve that, whenever a new