Bill Farner created AURORA-121:
----------------------------------
Summary: Make the preemptor more efficient
Key: AURORA-121
URL: https://issues.apache.org/jira/browse/AURORA-121
Project: Aurora
Issue Type: Story
Components: Scheduler
Reporter: Bill Farner
When {{TaskSchedulerImpl}} fails to find an open slot for a task, it falls back
to the preemptor:
{code}
if (!offerQueue.launchFirst(getAssignerFunction(taskId, task))) {
// Task could not be scheduled.
maybePreemptFor(taskId);
return TaskSchedulerResult.TRY_AGAIN;
}
{code}
This can be problematic when the task store is large (O(10k tasks)) and there
is a steady supply of PENDING tasks not satisfied by open slots. This will
manifest as an overall degraded/slow scheduler, and logs of slow queries used
for preemption:
{noformat}
I0125 17:47:36.970 THREAD23
org.apache.aurora.scheduler.storage.mem.MemTaskStore.fetchTasks: Query took 107
ms: TaskQuery(owner:null, environment:null, jobName:null,
taskIds:null, statuses:[KILLING, ASSIGNED, STARTING, RUNNING, RESTARTING],
slaveHost:null, instanceIds:null)
{noformat}
Several approaches come to mind to improve this situation:
- (easy) More aggressively back off on tasks that cannot be satisfied
- (easy) Fall back to preemption less frequently
- (harder) Scan for preemption candidates asynchronously, freeing up the
TaskScheduler thread and the storage write lock. Scans could be kicked off by
the task scheduler, ideally in a way that doesn't dogpile. This could also be
done in a weakly-consistent way to minimally contribute to storage contention.
--
This message was sent by Atlassian JIRA
(v6.1.5#6160)
