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From "Jordan Ly (JIRA)" <j...@apache.org>
Subject [jira] [Created] (AURORA-1949) PreemptionVictimFilterImpl comparator violates transitivity causing exceptions
Date Tue, 26 Sep 2017 23:10:00 GMT
Jordan Ly created AURORA-1949:
---------------------------------

             Summary: PreemptionVictimFilterImpl comparator violates transitivity causing
exceptions
                 Key: AURORA-1949
                 URL: https://issues.apache.org/jira/browse/AURORA-1949
             Project: Aurora
          Issue Type: Bug
          Components: Scheduler
            Reporter: Jordan Ly
            Priority: Critical


The PreemptionVictimFilterImpl uses a comparator to sort ResourceBags in order to preempt
the biggest tasks first when searching for a victim. However, the current implementation causes
an exception which causes the Scheduler to fail:

{noformat}
SEVERE: Service PreemptorService [FAILED] has failed in the RUNNING state.
java.lang.IllegalArgumentException: Comparison method violates its general contract!
        at java.util.TimSort.mergeLo(TimSort.java:777)
        at java.util.TimSort.mergeAt(TimSort.java:514)
        at java.util.TimSort.mergeCollapse(TimSort.java:441)
        at java.util.TimSort.sort(TimSort.java:245)
        at java.util.Arrays.sort(Arrays.java:1438)
        at com.google.common.collect.Ordering.immutableSortedCopy(Ordering.java:882)
        at org.apache.aurora.scheduler.preemptor.PreemptionVictimFilter$PreemptionVictimFilterImpl.filterPreemptionVictims(PreemptionVictimFilter.java:210)
        at org.apache.aurora.scheduler.preemptor.PendingTaskProcessor.lambda$run$0(PendingTaskProcessor.java:178)
        at org.apache.aurora.scheduler.storage.db.DbStorage.read(DbStorage.java:147)
        at org.mybatis.guice.transactional.TransactionalMethodInterceptor.invoke(TransactionalMethodInterceptor.java:101)
        at org.apache.aurora.common.inject.TimedInterceptor.invoke(TimedInterceptor.java:83)
        at org.apache.aurora.scheduler.storage.log.LogStorage.read(LogStorage.java:562)
        at org.apache.aurora.scheduler.storage.CallOrderEnforcingStorage.read(CallOrderEnforcingStorage.java:113)
        at org.apache.aurora.scheduler.preemptor.PendingTaskProcessor.run(PendingTaskProcessor.java:135)
        at org.apache.aurora.common.inject.TimedInterceptor.invoke(TimedInterceptor.java:83)
        at org.apache.aurora.scheduler.preemptor.PreemptorModule$PreemptorService.runOneIteration(PreemptorModule.java:205)
        at com.google.common.util.concurrent.AbstractScheduledService$ServiceDelegate$Task.run(AbstractScheduledService.java:188)
        at com.google.common.util.concurrent.Callables$4.run(Callables.java:122)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)
{noformat}

Looking at the code, it seems it violates transitivity:

{code:java}
    @VisibleForTesting
    static final Ordering<ResourceBag> ORDER = new Ordering<ResourceBag>() {
      @Override
      public int compare(ResourceBag left, ResourceBag right) {
        Set<ResourceType> types = ImmutableSet.<ResourceType>builder()
            .addAll(left.streamResourceVectors().map(e -> e.getKey()).iterator())
            .addAll(right.streamResourceVectors().map(e -> e.getKey()).iterator())
            .build();

        boolean allZero = true;
        boolean allGreaterOrEqual = true;
        boolean allLessOrEqual = true;

        for (ResourceType type : types) {
          int compare = left.valueOf(type).compareTo(right.valueOf(type));
          if (compare != 0) {
            allZero = false;
          }

          if (compare < 0) {
            allGreaterOrEqual = false;
          }

          if (compare > 0) {
            allLessOrEqual = false;
          }
        }

        if (allZero) {
          return 0;
        }

        if (allGreaterOrEqual) {
          return 1;
        }

        if (allLessOrEqual) {
          return -1;
        }

        return 0;
      }
    };
{code}

The example below illustrates the error:

{noformat}
Resource: X Y Z
Bag A:       2 0 2
Bag B:       1 2 1
Bag C:       2 2 1
{noformat}

We can see that A = B, B < C, and C = A which would cause an exception.

There are a couple of routes we can take to solve this. What we really want is to be able
to define partial ordering (comparator does total ordering) so we can do a topological sort.
Additionally, we can give priority to particular resources (Dominant Resource Fairness).




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