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Coordinator drop segment selection through cost balancer #5529

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merged 6 commits into from
Apr 3, 2018
Merged

Coordinator drop segment selection through cost balancer #5529

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67b9b85
drop selection through cost balancer
clintropolis Mar 23, 2018
ab010ff
use collections.emptyIterator
clintropolis Mar 24, 2018
5af6061
add test to ensure does not drop from server with larger loading queu…
clintropolis Mar 30, 2018
7b2bd2e
Merge remote-tracking branch 'upstream/master' into coordinator-drop-…
clintropolis Apr 2, 2018
268abfa
javadocs and comments to clear things up
clintropolis Apr 2, 2018
106d834
random drop for completeness
clintropolis Apr 2, 2018
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7 changes: 7 additions & 0 deletions server/src/main/java/io/druid/server/coordinator/BalancerStrategy.java
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Expand Up @@ -21,7 +21,9 @@

import io.druid.timeline.DataSegment;

import java.util.Iterator;
import java.util.List;
import java.util.NavigableSet;

public interface BalancerStrategy
{
Expand All @@ -31,5 +33,10 @@ public interface BalancerStrategy

BalancerSegmentHolder pickSegmentToMove(List<ServerHolder> serverHolders);

default Iterator<ServerHolder> pickServersToDrop(DataSegment toDropSegment, NavigableSet<ServerHolder> serverHolders)
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This should have some javadoc explaining what the returned iterator should be. It's non-obvious: the "obvious" return value would be a set of servers to drop from, where the order doesn't matter. But the actual return value is ordered by preferredness, and may contain more servers than we actually want to drop from.

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I went ahead and added javadoc for whole interface, lmk if I got anything wrong

{
return serverHolders.descendingIterator();
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Would be nice to include a comment about why this descendingIterator is meaningful. (Like the comment on the old code: // Use the reverse order to get the holders with least available size first.)

}

void emitStats(String tier, CoordinatorStats stats, List<ServerHolder> serverHolderList);
}
43 changes: 34 additions & 9 deletions server/src/main/java/io/druid/server/coordinator/CostBalancerStrategy.java
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Expand Up @@ -32,9 +32,13 @@
import org.joda.time.Interval;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.NavigableSet;
import java.util.concurrent.ThreadLocalRandom;
import java.util.stream.Collectors;

public class CostBalancerStrategy implements BalancerStrategy
{
Expand Down Expand Up @@ -219,6 +223,34 @@ public BalancerSegmentHolder pickSegmentToMove(final List<ServerHolder> serverHo
return sampler.getRandomBalancerSegmentHolder(serverHolders);
}

@Override
public Iterator<ServerHolder> pickServersToDrop(DataSegment toDrop, NavigableSet<ServerHolder> serverHolders)
{
List<ListenableFuture<Pair<Double, ServerHolder>>> futures = Lists.newArrayList();

for (final ServerHolder server : serverHolders) {
futures.add(
exec.submit(
() -> Pair.of(computeCost(toDrop, server, true), server)
)
);
}

final ListenableFuture<List<Pair<Double, ServerHolder>>> resultsFuture = Futures.allAsList(futures);

try {
List<Pair<Double, ServerHolder>> results = resultsFuture.get();
return results.stream()
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This code is slightly obtuse (what's the double? why reverse it?) and would benefit from a comment.

.sorted(Comparator.comparingDouble((Pair<Double, ServerHolder> o) -> o.lhs).reversed())
.map(x -> x.rhs).collect(Collectors.toList())
.iterator();
}
catch (Exception e) {
log.makeAlert(e, "Cost Balancer Multithread strategy wasn't able to complete cost computation.").emit();
}
return Collections.emptyIterator();
}

/**
* Calculates the initial cost of the Druid segment configuration.
*
Expand Down Expand Up @@ -341,14 +373,7 @@ protected Pair<Double, ServerHolder> chooseBestServer(
for (final ServerHolder server : serverHolders) {
futures.add(
exec.submit(
new Callable<Pair<Double, ServerHolder>>()
{
@Override
public Pair<Double, ServerHolder> call()
{
return Pair.of(computeCost(proposalSegment, server, includeCurrentServer), server);
}
}
() -> Pair.of(computeCost(proposalSegment, server, includeCurrentServer), server)
)
);
}
Expand Down
18 changes: 12 additions & 6 deletions server/src/main/java/io/druid/server/coordinator/rules/LoadRule.java
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Expand Up @@ -19,8 +19,9 @@

package io.druid.server.coordinator.rules;

import io.druid.java.util.emitter.EmittingLogger;
import io.druid.java.util.common.IAE;
import io.druid.java.util.emitter.EmittingLogger;
import io.druid.server.coordinator.BalancerStrategy;
import io.druid.server.coordinator.CoordinatorStats;
import io.druid.server.coordinator.DruidCluster;
import io.druid.server.coordinator.DruidCoordinator;
Expand All @@ -39,6 +40,7 @@
import java.util.Map;
import java.util.NavigableSet;
import java.util.Objects;
import java.util.TreeSet;
import java.util.function.Predicate;
import java.util.stream.Collectors;

Expand Down Expand Up @@ -209,7 +211,7 @@ private ServerHolder assignPrimary(
}

/**
* @param stats {@link CoordinatorStats} to accumulate assignment statistics.
* @param stats {@link CoordinatorStats} to accumulate assignment statistics.
* @param tierToSkip if not null, this tier will be skipped from doing assignment, use when primary replica was
* assigned.
*/
Expand Down Expand Up @@ -320,7 +322,7 @@ private void drop(
} else {
final int currentReplicantsInTier = entry.getIntValue();
final int numToDrop = currentReplicantsInTier - targetReplicants.getOrDefault(tier, 0);
numDropped = dropForTier(numToDrop, holders, segment);
numDropped = dropForTier(numToDrop, holders, segment, params.getBalancerStrategy());
}

stats.addToTieredStat(DROPPED_COUNT, tier, numDropped);
Expand All @@ -346,13 +348,17 @@ private boolean loadingInProgress(final DruidCluster druidCluster)
private static int dropForTier(
final int numToDrop,
final NavigableSet<ServerHolder> holdersInTier,
final DataSegment segment
final DataSegment segment,
final BalancerStrategy balancerStrategy
)
{
int numDropped = 0;

// Use the reverse order to get the holders with least available size first.
final Iterator<ServerHolder> iterator = holdersInTier.descendingIterator();
final NavigableSet<ServerHolder> isServingSubset =
holdersInTier.stream().filter(s -> s.isServingSegment(segment)).collect(Collectors.toCollection(TreeSet::new));
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There's still a (now pointless) check for isServingSegment below. It should be removed lest it confuse people.

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I left the check in case in the time between the initial filtering and the loop something changed and the server was no longer serving the segment, but I can remove the extra check if you think it's safe.

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If there is a race between pickServersToDrop and this line, then there's still a race even with the check. I think it's ok to leave the check in, but maybe log a warning if it actually gets tripped. (We don't expect it to unless there is some race)

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👍 added log.warn


final Iterator<ServerHolder> iterator = balancerStrategy.pickServersToDrop(segment, isServingSubset);

while (numDropped < numToDrop) {
if (!iterator.hasNext()) {
log.warn("Wtf, holder was null? I have no servers serving [%s]?", segment.getIdentifier());
Expand Down
124 changes: 116 additions & 8 deletions server/src/test/java/io/druid/server/coordinator/DruidCoordinatorRuleRunnerTest.java
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Expand Up @@ -22,6 +22,7 @@
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.common.collect.Sets;
import com.google.common.util.concurrent.ListeningExecutorService;
import com.google.common.util.concurrent.MoreExecutors;
import io.druid.client.DruidServer;
Expand Down Expand Up @@ -712,6 +713,98 @@ public void testDropTooManyInSameTier()
EasyMock.verify(mockPeon);
}

@Test
public void testDropTooManyInSameTierWithLoadQueue()
{
mockCoordinator();
mockPeon.dropSegment(EasyMock.<DataSegment>anyObject(), EasyMock.<LoadPeonCallback>anyObject());
EasyMock.expectLastCall().atLeastOnce();
mockEmptyPeon();

LoadQueuePeon loadingPeon = EasyMock.createMock(LoadQueuePeon.class);
mockLoadingPeon(loadingPeon, availableSegments.size() + 10, availableSegments.size());

EasyMock.expect(databaseRuleManager.getRulesWithDefault(EasyMock.<String>anyObject())).andReturn(
Lists.<Rule>newArrayList(
new IntervalLoadRule(
Intervals.of("2012-01-01T00:00:00.000Z/2012-01-01T12:00:00.000Z"),
ImmutableMap.<String, Integer>of("normal", 1)
),
new IntervalDropRule(Intervals.of("2012-01-01T00:00:00.000Z/2012-01-02T00:00:00.000Z"))
)
).atLeastOnce();
EasyMock.replay(databaseRuleManager);

DruidServer server1 = new DruidServer(
"serverNorm",
"hostNorm",
null,
1000,
ServerType.HISTORICAL,
"normal",
0
);
server1.addDataSegment(availableSegments.get(0));
server1.addDataSegment(availableSegments.get(1));

DruidServer server2 = new DruidServer(
"serverNorm2",
"hostNorm2",
null,
1000,
ServerType.HISTORICAL,
"normal",
0
);
for (DataSegment segment : availableSegments.subList(1, availableSegments.size())) {
server2.addDataSegment(segment);
}

DruidCluster druidCluster = new DruidCluster(
null,
ImmutableMap.of(
"normal",
Stream.of(
new ServerHolder(
server1.toImmutableDruidServer(),
loadingPeon
),
new ServerHolder(
server2.toImmutableDruidServer(),
mockPeon
)
).collect(Collectors.toCollection(() -> new TreeSet<>(Collections.reverseOrder())))
)
);

SegmentReplicantLookup segmentReplicantLookup = SegmentReplicantLookup.make(druidCluster);

ListeningExecutorService exec = MoreExecutors.listeningDecorator(
Executors.newFixedThreadPool(1));
BalancerStrategy balancerStrategy =
new CostBalancerStrategyFactory().createBalancerStrategy(exec);

DruidCoordinatorRuntimeParams params = new DruidCoordinatorRuntimeParams.Builder()
.withDruidCluster(druidCluster)
.withDynamicConfigs(CoordinatorDynamicConfig.builder().withMillisToWaitBeforeDeleting(0L).build())
.withAvailableSegments(availableSegments)
.withDatabaseRuleManager(databaseRuleManager)
.withSegmentReplicantLookup(segmentReplicantLookup)
.withBalancerStrategy(balancerStrategy)
.withBalancerReferenceTimestamp(DateTimes.of("2013-01-01"))
.build();

DruidCoordinatorRuntimeParams afterParams = ruleRunner.run(params);
CoordinatorStats stats = afterParams.getCoordinatorStats();

Assert.assertEquals(1L, stats.getTieredStat("droppedCount", "normal"));
Assert.assertEquals(12L, stats.getGlobalStat("deletedCount"));

exec.shutdown();
EasyMock.verify(mockPeon);
EasyMock.verify(loadingPeon);
}

@Test
public void testDropTooManyInDifferentTiers()
{
Expand Down Expand Up @@ -761,9 +854,9 @@ public void testDropTooManyInDifferentTiers()
ImmutableMap.of(
"hot",
Stream.of(
new ServerHolder(
server1.toImmutableDruidServer(),
mockPeon
new ServerHolder(
server1.toImmutableDruidServer(),
mockPeon
)
).collect(Collectors.toCollection(() -> new TreeSet<>(Collections.reverseOrder()))),
"normal",
Expand Down Expand Up @@ -942,6 +1035,7 @@ public void testDropServerActuallyServesSegment()

LoadQueuePeon anotherMockPeon = EasyMock.createMock(LoadQueuePeon.class);
EasyMock.expect(anotherMockPeon.getLoadQueueSize()).andReturn(10L).atLeastOnce();
EasyMock.expect(anotherMockPeon.getSegmentsToLoad()).andReturn(Sets.newHashSet()).anyTimes();
EasyMock.replay(anotherMockPeon);

DruidCluster druidCluster = new DruidCluster(
Expand Down Expand Up @@ -1409,11 +1503,25 @@ private void mockCoordinator()

private void mockEmptyPeon()
{
EasyMock.expect(mockPeon.getSegmentsToLoad()).andReturn(new HashSet<>()).anyTimes();
EasyMock.expect(mockPeon.getSegmentsMarkedToDrop()).andReturn(new HashSet<>()).anyTimes();
EasyMock.expect(mockPeon.getLoadQueueSize()).andReturn(0L).atLeastOnce();
EasyMock.expect(mockPeon.getNumberOfSegmentsInQueue()).andReturn(0).anyTimes();
EasyMock.replay(mockPeon);
mockEmptyPeon(mockPeon);
}

private void mockEmptyPeon(LoadQueuePeon peon)
{
EasyMock.expect(peon.getSegmentsToLoad()).andReturn(new HashSet<>()).anyTimes();
EasyMock.expect(peon.getSegmentsMarkedToDrop()).andReturn(new HashSet<>()).anyTimes();
EasyMock.expect(peon.getLoadQueueSize()).andReturn(0L).atLeastOnce();
EasyMock.expect(peon.getNumberOfSegmentsInQueue()).andReturn(0).anyTimes();
EasyMock.replay(peon);
}

private void mockLoadingPeon(LoadQueuePeon peon, long size, int segments)
{
EasyMock.expect(peon.getSegmentsToLoad()).andReturn(new HashSet<>()).anyTimes();
EasyMock.expect(peon.getSegmentsMarkedToDrop()).andReturn(new HashSet<>()).anyTimes();
EasyMock.expect(peon.getLoadQueueSize()).andReturn(size).atLeastOnce();
EasyMock.expect(peon.getNumberOfSegmentsInQueue()).andReturn(segments).anyTimes();
EasyMock.replay(peon);
}

private CoordinatorDynamicConfig createCoordinatorDynamicConfig()
Expand Down
7 changes: 6 additions & 1 deletion server/src/test/java/io/druid/server/coordinator/rules/LoadRuleTest.java
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Expand Up @@ -286,6 +286,9 @@ public void testDrop()
final LoadQueuePeon mockPeon = createEmptyPeon();
mockPeon.dropSegment(EasyMock.anyObject(), EasyMock.anyObject());
EasyMock.expectLastCall().atLeastOnce();
EasyMock.expect(mockBalancerStrategy.pickServersToDrop(EasyMock.anyObject(), EasyMock.anyObject()))
.andDelegateTo(balancerStrategy)
.times(2);
EasyMock.replay(throttler, mockPeon, mockBalancerStrategy);

LoadRule rule = createLoadRule(ImmutableMap.of(
Expand Down Expand Up @@ -430,7 +433,9 @@ public void testDropWithNonExistentTier()
final LoadQueuePeon mockPeon = createEmptyPeon();
mockPeon.dropSegment(EasyMock.anyObject(), EasyMock.anyObject());
EasyMock.expectLastCall().atLeastOnce();

EasyMock.expect(mockBalancerStrategy.pickServersToDrop(EasyMock.anyObject(), EasyMock.anyObject()))
.andDelegateTo(balancerStrategy)
.times(1);
EasyMock.replay(throttler, mockPeon, mockBalancerStrategy);

LoadRule rule = createLoadRule(ImmutableMap.of(
Expand Down