1. A method for processing a plurality of transactions using graph-based computations executed on a computer system including one or more processors, memory, and at least one input device coupled to a data source providing a flow of work elements, the method comprising: for a first transaction of the plurality of transactions, associating a computation graph with the first transaction, the computation graph including a plurality of executing processes, each executing process having one or more inputs and one or more outputs, and the computation graph including one or more links that each represent a flow of work elements between an output of an upstream executing process and an input of a downstream executing process; activating an instance of the computation graph to process work elements from the data source associated with the plurality of transactions, including allocating a portion of the memory to the instance; allocating the instance to the first transaction; executing the instance to process work elements associated with the first transaction; outputting terminators on links from upstream executing processes to downstream executing processes to indicate that the upstream executing processes have completed processing work elements associated with the first transaction; allocating the instance to a second transaction of the plurality of transactions associated with the computation graph; executing the instance to process work elements associated with the second transaction; and outputting terminators on links from upstream executing processes to downstream executing processes to indicate that the upstream executing processes have completed processing work elements associated with the second transaction.