What is it a distributed runtime uses pipelines for execution exactly-once state consistency lightweight checkpoint iterative processing windows semantics out-of-order processing 2 architecture cluster client job manager task manager (1 or more) client takes a program xforms to dataflow graph submits to job manager creates data schema and serializers cost-based query optmization job manager coordinates distributed execution of dataflow tracks state and progress of each operator and stream schedules new operators coordinates checkpoints and recovery persists minimal set of data for checkpoint and recovery task manager executes one or more operators report status to job manager maintain buffer pools to buffer or materialize streams maintain network connections to exchange of streams between operators 3.