One embodiment provides a method comprising storing a first set of explicitly enumerated data values in a first window data structure associated with a first time span. The method further comprises storing one or more sets of summary statistics in a second set of window data structures. Each window data structure of the second set of window data structures is associated with a time span older than the first time span. The one or more sets of summary statistics are based on a second set of data values. The method further comprises storing a third set of explicitly enumerated data values in a third set of window data structures, wherein each data value of the third set of explicitly enumerated data values is annotated.