title: Is CEP what I need (system state and event replaying)
body: <p>I'm looking for a CEP engine, but I' don't know if any engine meets my requirements.
  My system has to process multiple streams of event data and generate complex events and this is exactly what almost any CEP engine perfectly fits (ESPER, Drools).</p>
  
  <p>I store all raw events in database (it's not CEP part, but I do this) and use rules (or continious queries or something) to generate custom actions on complex events. But some of my rules are dependent on the events in the past.
  For instance: I could have a sensor sending event everytime my spouse is coming or leaving home and if both my car and the car of my fancy woman are near the house, I get SMS 'Dangerous'.</p>
  
  <p>The problem is that with restart of event processing service I lose all information on the state of the system (is my wife at home?) and to restore it I need to replay events for unknow period of time. The system state can depend not only on raw events, but on complex events as well.</p>
  
  <p>The same problem arises when I need some report on complex events in the past. I have raw events data stored in database, and could generate these complex events replaying raw events, but I don't know for which exactly period I have to replay them.</p>
  
  <p>At the same time it's clear that for the most rules it's possible to find automatically the number of events to be processed from the past (or period of time to load events to be processed) to restore system state.
  If given action depends on presence of my wife at home, CEP system has to request last status change. If report on complex events is requested and complex event depends on average price within the previous period, all price change events for this period should be replayed. And so on...</p>
  
  <p>If I miss something? </p>