A priority based scheduling system for a server prioritizes multiple tasks that are defined using various constraints, which may include relationships defined between different tasks, performance parameters for each task, and completion constraints. The system may track actual performance of a task and update the performance parameters over time. Some embodiments may include a status monitoring agent that may detect that a monitored network parameter has changed that may cause a scheduled task to be raised or lowered in priority. The system may be used to schedule and execute one time tasks as well as recurring tasks, and may execute those tasks during a rigid or flexible periodic time window. Many of the tasks may be pausable and resumable, and such tasks may be performed in increments over successive time windows.