[jira] [Created] (AURORA-1802) AttributeAggregate slows down scheduling of jobs with many instances

["Stephan Erb (JIRA)" <ji...@apache.org>]

Stephan Erb created AURORA-1802:
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             Summary: AttributeAggregate slows down scheduling of jobs with many instances
                 Key: AURORA-1802
                 URL: https://issues.apache.org/jira/browse/AURORA-1802
             Project: Aurora
          Issue Type: Bug
          Components: Scheduler
            Reporter: Stephan Erb


The current implementation of [{{AttributeAggregate}}|https://github.com/apache/aurora/blob/f559e930659e25b3d7cacb7b845ebda50d18d66a/src/main/java/org/apache/aurora/scheduler/filter/AttributeAggregate.java] slows down scheduling of jobs with many instances. Interestingly, this is currently not visible in our job scheduling benchmark results as it only affects the benchmark setup time but not the measured part.

{{AttributeAggregate}} relies on {{Suppliers.memoize}} to ensure that it is only computed once and only when necessary. This has probably been done because the factory [{{AttributeAggregate.getJobActiveState}}|https://github.com/apache/aurora/blob/f559e930659e25b3d7cacb7b845ebda50d18d66a/src/main/java/org/apache/aurora/scheduler/filter/AttributeAggregate.java#L56-L91] is slow. 

After some recent changes to schedule multiple task instances per scheduling round the aggregate is computed in each scheduling round via the call [{{resourceRequest.getJobState().updateAttributeAggregate(...)}} |https://github.com/apache/aurora/blob/f559e930659e25b3d7cacb7b845ebda50d18d66a/src/main/java/org/apache/aurora/scheduler/state/TaskAssigner.java#L173] in {{TaskAssigner}}. This means the expensive factory is called once per scheduling round.

h3. Potential improvements

* the current factory implementation performs one {{fetchTasks}} query followed by {{n}} distinct {{getHostAttributes}} queries. This could be reduced to a single SQL query.
* the aggregate makes heavy use of {{ImmutableMultiset}} even though it is not immutable any more. There is potential room for improvement here.
* The aggregate uses suppliers to perform a lazy instantiation even though its current usage is not lazy any more. We can either make the implementation eager, or ensure that the expensive part is only run when absolutely necessary.






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