A method to create a partition by time/tuple based window in an event processing service is provided. When continuous data streams are received, tuples are stored in a data structure with partitions based upon partition keys. Only a specified amount of tuples may be stored in each partition. When a partition exceeds the specified number of tuples, the oldest tuples are removed from the data structure. Tuples stored beyond a specified time period are also removed from the data structure. Two data structures may also be used to implement a time/tuple based window. Tuples are stored in both a data structure with a partition by window and a data structure with a range window. Tuples are removed in the partition by window when tuples exceed the amount in the partition. Tuples are removed in the range window when tuples exceed a specified time period. The two data structures are synchronized.