1. A method for performing event processing comprising: receiving, by a computer system, an event stream comprising a plurality of events each having an event key of a plurality of event keys associated therewith; instantiating, by the computer system, a plurality of target instances being executable objects each having an instance key of a plurality of instance keys associated therewith; assigning, by the computer system, each target instance of the plurality of target instances for execution within a thread of a plurality of threads executing on the computer system; for each event of the plurality of events in the event stream, mapping, by the computer system, the each event to at least one target instance of the plurality of target instances having the instance key thereof identical to the event key of the each event and storing the each event in at least one queue of a plurality of queues each corresponding to a thread of the plurality of threads; evaluating, by the computer system, loading of the plurality of queues to identify one or more overloaded queues; in response to the evaluation, reassigning, by the computer system, one or more target instances from one or more threads of the plurality of threads associated with the one or more overloaded queues to one or more other threads of the plurality of threads that are not overloaded; and processing, by the computer system, events of the plurality of events in a queue of the plurality of queues corresponding to each thread of the plurality of threads by, for each event of the events: retrieving the each event from the queue of the plurality of queues corresponding to the each thread; evaluating the at least one target instance mapped to the each event; if the at least one target instance mapped to the each event has been reassigned to a different thread of the plurality of threads subsequent to adding of the each event to the queue of the plurality of queues corresponding to the each thread, moving the each event to the queue of the plurality of queues corresponding to a different thread of the plurality of threads; and if the at least one target instance mapped to the each event has not been reassigned to a different thread of the plurality of threads subsequent to adding of the each event to the queue of the plurality of queues corresponding to the each thread, processing the each event by the target instance within the each thread, wherein: each event includes an attribute and value pair.