1. A computer-implemented method, comprising: providing a plurality of processing elements comprising one or more operators, the operators configured to process streaming data tuples; establishing an operator graph of a plurality of operators, the operator graph defining at least one execution path in which a first operator of the plurality of operators is configured to: (i) receive data tuples from at least one upstream operator and (ii) transmit data tuples to at least one downstream operator, wherein the first operator executes on a first compute node of a plurality of compute nodes; monitoring a memory use by the first operator on the first compute node; determining that the memory use of the first operator exceeds a memory threshold; determining that metadata associated with the first operator specifies to transfer state data of a first variable of the first operator; moving the first operator and, based on the metadata, the state data of the first variable to a second compute node, of the plurality of compute nodes; and starting the first operator on the second compute node.