In a nutshell, Corona represents a new system for scheduling Hadoop jobs that makes better use of a cluster’s resources and also makes it more amenable to multitenant environments like the one Facebook operates. Ching et al explain the problems and the solution in some detail, but the short explanation is that Hadoop’s JobTracker node is responsible for both cluster management and job-scheduling, but has a hard time keeping up with both tasks as clusters grow and the number of jobs sent to them increase.
Further, job-scheduling in Hadoop involves an inherent delay, which is problematic for small jobs that need fast results. And a fixed configuration of “map” and “reduce” slots means Hadoop clusters run inefficiently when jobs don’t fit into the remaining slots or when they’re not MapReduce jobs at all.
Corona resolves some of these problems by creating individual job trackers for each job and a cluster manager focused solely on tracking nodes and the amount of available resources. Th