Stateful computing involves storing and retrieving state while evaluating expressions in an Expression transformation.
Configure partitioning by specifying one or more columns under partition keys on the
Windowing
tab.
Configure the partition keys to define partition boundaries, rather than performing the calculation across all inputs.
If you do not define partition keys, all the data is included in the same partition. The variable values stored will be global and every row can read and update the same set of variables.
To improve mapping performance, configure partition keys.