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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