Scheduler state machine Scheduling is independent of semantics Vertex can run anywhere once all its inputs are read Constraints/hints place it near its inputs Fault tolerance If A fails, run it again If a's inputs are gone run upstream vertices again recursive If a is slow, run another copy elsewhere and use output from whichever finishes firstScheduler state machine • Scheduling is independent of semantics – Vertex can run anywhere once all its inputs are ready • Constraints/hints place it near its inputs – Fault tolerance • If A fails, run it again • If A’s inputs are gone, run upstream vertices again (recursively) • If A is slow, run another copy elsewhere and use output from whichever finishes first