A method comprising: receiving an event at a first computing node of a stream processing system, wherein the stream processing system comprises one or more computing nodes (310 A, 310 B, 310 N) representing a stream processing topology of functional modules, wherein each functional module defines one or more operations to be performed on an event and an output destination for the event, and wherein all functional modules of the stream processing topology are installed on each of the computing nodes (310 A, 310 B, 310 N); at a first functional module of the topology, determining that an operation requests access to context data (314 A, 314 B, 314 C) related to the event based on a data attribute of the event, wherein said context data (314 A, 314 B, 314 C) is pre-existing data related to the event in a stream of events and includes data that does not occur within data attributes of the event, wherein the context data (314 A, 314 B, 314 C) is partitioned among the one or more computing nodes (310 A, 310 B, 310 N), and wherein each partition of context data is stored in operational memory of the respective computing node; determining that the context data (314 B) required by the first functional module is not located in the operational memory of the first computing node (310 A); routing the event to a particular second functional module of a second computing node that has the required context data (314 B) in operational memory, the first and the second functional modules defining the same one or more operations to be performed on an event; obtaining, from the operational memory of the second computing node (310 B), the context data (314 B) related to the event; processing the operation of the particular second functional module using the context data (314 B) obtained from the operational memory of the second computing node (310 B) including generating a modified event; and providing the modified event to a subsequent functional module of the second computing node according to the topology of functional modules, wherein each functional module of the stream processing topology executes within a same operating system process of the computing node (310 A, 310 B, 310 N) of the stream processing system and each partition of the context data (314 A, 314 B, 314 C) is maintained in operational memory by said same operating system process. receiving an event at a first computing node of a stream processing system, wherein the stream processing system comprises one or more computing nodes (310 A, 310 B, 310 N) representing a stream processing topology of functional modules, wherein each functional module defines one or more operations to be performed on an event and an output destination for the event, and wherein all functional modules of the stream processing topology are installed on each of the computing nodes (310 A, 310 B, 310 N); at a first functional module of the topology, determining that an operation requests access to context data (314 A, 314 B, 314 C) related to the event based on a data attribute of the event, wherein said context data (314 A, 314 B, 314 C) is pre-existing data related to the event in a stream of events and includes data that does not occur within data attributes of the event, wherein the context data (314 A, 314 B, 314 C) is partitioned among the one or more computing nodes (310 A, 310 B, 310 N), and wherein each partition of context data is stored in operational memory of the respective computing node; determining that the context data (314 B) required by the first functional module is not located in the operational memory of the first computing node (310 A); routing the event to a particular second functional module of a second computing node that has the required context data (314 B) in operational memory, the first and the second functional modules defining the same one or more operations to be performed on an event; obtaining, from the operational memory of the second computing node (310 B), the context data (314 B) related to the event; processing the operation of the particular second functional module using the context data (314 B) obtained from the operational memory of the second computing node (310 B) including generating a modified event; and providing the modified event to a subsequent functional module of the second computing node according to the topology of functional modules, wherein each functional module of the stream processing topology executes within a same operating system process of the computing node (310 A, 310 B, 310 N) of the stream processing system and each partition of the context data (314 A, 314 B, 314 C) is maintained in operational memory by said same operating system process.