[MAPREDUCE-251] Should we move out the creation of setup/cleanup tasks from JobInProgress.initTasks()?

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Amareshwari Sriramadasu
• Reporter: Vivek Ratan
• Created: 21/Oct/08 10:01
• Updated: 20/Jun/09 07:51

Description

JobInProgress.initTasks() creates TIPs for map and reduce tasks, and also the newly-introduced setup and cleanup tasks. initTasks() is called by the schedulers, as for reasons of memory optimizations, schedulers may choose to initialize M/R tasks at various moments (the Capacity Scheduler, for example, calls initTasks() just when it considers a job for running). One can say that Schedulers 'own' the initialization of M/R tasks in a job. Furthermore the JT 'owns' the setup and cleanup tasks (it schedules them, and Schedulers are unaware of these tasks). This causes a problematic dependency between the JT and a Scheduler. For example, the Capacity Scheduler calls initTasks() and immediately calls JobInProgress.obtainNewMapTask for a map task. This is a problem today, because we cannot run any map or reduce tasks before the setup task is run, which the Capacity Scheduler is not aware of.

Either all Schedulers are explicitly aware of setup/cleanup tasks and their dependencies with M/R tasks (in which case, Schedulers 'own' the creation and scheduling of all these tasks correctly), or the JT 'owns' the setup/cleanup tasks and Schedulers are completely unaware of them (in which case, the creation of setup/cleanup tasks must be moved out of initTasks into a separate method which is called by the JT).

I think the latter is the right way to go (unless we implement HADOOP-4421, in which case the former option may be viable as well).

Issue Links

• relates to: MAPREDUCE-138 Rework job-setup and job-cleanup tasks