MapReduce "Runtime" a Handles scheduling Assigns workers to map and reduce tasks Handles "data distribution" Moves processes to data Handles synchronization Gathers,sorts,and shuffles intermediate data Handles errors and faults Detects worker failures and restarts -Everything happens on top of a distributed FS (later)MapReduce “Runtime” ◼ Handles scheduling ◼ Assigns workers to map and reduce tasks ◼ Handles “data distribution” ◼ Moves processes to data ◼ Handles synchronization ◼ Gathers, sorts, and shuffles intermediate data ◼ Handles errors and faults ◼ Detects worker failures and restarts ◼ Everything happens on top of a distributed FS (later)