This short paper provides an overview of the DejaVu complex event processing (CEP) system, with an emphasis on its novel architecture and query optimization techniques for correlating patterns across live and historical data streams. Categories and Subject Descriptors H.2.4 [Database Management]: Systems - Query Processing General Terms Performance, Languages, Theory 							
						
							
					 															
					Nihal Dindar, Peter M. Fischer, Nesime Tatbul