1. A method by a processing system to control recovery of operational state values of a complex event processing (CEP) engine that processes values of events, the method comprising: determining a window size based on a property of an event query; retrieving events' values, from a distributed log, that are restricted to occurring within a timeframe defined based on the window size, wherein the distributed log stores events' values that have been processed by the CEP engine; and replaying the retrieved events' values to the CEP engine for processing to recover the operational state values of the CEP engine, wherein the window size is determined based on a time value contained in the event query, the time value indicates a time duration over which an operation defined by the event query is to be periodically performed on an incoming stream of events values to the CEP engine, and the operation defined by the event query computes an average duration of SIP INVITES for an entity defined by the event query.