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[Backport] Coordinator fix balance to try to move max segments instead of up to max segments #5974

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[Backport] Coordinator fix balance to try to move max segments instead of up to max segments #5974

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35 changes: 24 additions & 11 deletions server/src/main/java/io/druid/server/coordinator/helper/DruidCoordinatorBalancer.java
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Original file line number Diff line number Diff line change
Expand Up @@ -20,9 +20,9 @@
package io.druid.server.coordinator.helper;

import com.google.common.collect.Lists;
import io.druid.java.util.emitter.EmittingLogger;
import io.druid.client.ImmutableDruidServer;
import io.druid.java.util.common.StringUtils;
import io.druid.java.util.emitter.EmittingLogger;
import io.druid.server.coordinator.BalancerSegmentHolder;
import io.druid.server.coordinator.BalancerStrategy;
import io.druid.server.coordinator.CoordinatorStats;
Expand All @@ -40,6 +40,7 @@
import java.util.NavigableSet;
import java.util.SortedSet;
import java.util.concurrent.ConcurrentHashMap;
import java.util.stream.Collectors;

/**
*/
Expand Down Expand Up @@ -103,44 +104,56 @@ private void balanceTier(
return;
}

final List<ServerHolder> serverHolderList = Lists.newArrayList(servers);
final List<ServerHolder> toMoveFrom = Lists.newArrayList(servers);
final List<ServerHolder> toMoveTo = Lists.newArrayList(servers);

if (serverHolderList.size() <= 1) {
if (toMoveTo.size() <= 1) {
log.info("[%s]: One or fewer servers found. Cannot balance.", tier);
return;
}

int numSegments = 0;
for (ServerHolder server : serverHolderList) {
for (ServerHolder server : toMoveFrom) {
numSegments += server.getServer().getSegments().size();
}

if (numSegments == 0) {
log.info("No segments found. Cannot balance.");
return;
}

final int maxToLoad = params.getCoordinatorDynamicConfig().getMaxSegmentsInNodeLoadingQueue();
long unmoved = 0L;
for (int iter = 0; iter < maxSegmentsToMove; iter++) {
final BalancerSegmentHolder segmentToMove = strategy.pickSegmentToMove(serverHolderList);
for (int moved = 0; (moved + unmoved) < maxSegmentsToMove;) {
final BalancerSegmentHolder segmentToMove = strategy.pickSegmentToMove(toMoveFrom);

if (segmentToMove != null && params.getAvailableSegments().contains(segmentToMove.getSegment())) {
final ServerHolder holder = strategy.findNewSegmentHomeBalancer(segmentToMove.getSegment(), serverHolderList);
final List<ServerHolder> toMoveToWithLoadQueueCapacity =
toMoveTo.stream()
.filter(s -> maxToLoad <= 0 || s.getNumberOfSegmentsInQueue() < maxToLoad)
.collect(Collectors.toList());

if (holder != null) {
moveSegment(segmentToMove, holder.getServer(), params);
final ServerHolder destinationHolder =
strategy.findNewSegmentHomeBalancer(segmentToMove.getSegment(), toMoveToWithLoadQueueCapacity);

if (destinationHolder != null) {
moveSegment(segmentToMove, destinationHolder.getServer(), params);
moved++;
} else {
++unmoved;
log.info("Segment [%s] is 'optimally' placed.", segmentToMove.getSegment().getIdentifier());
unmoved++;
}
}
}

if (unmoved == maxSegmentsToMove) {
// Cluster should be alive and constantly adjusting
log.info("No good moves found in tier [%s]", tier);
}
stats.addToTieredStat("unmovedCount", tier, unmoved);
stats.addToTieredStat("movedCount", tier, currentlyMovingSegments.get(tier).size());
if (params.getCoordinatorDynamicConfig().emitBalancingStats()) {
strategy.emitStats(tier, stats, serverHolderList);
strategy.emitStats(tier, stats, toMoveFrom);
}
log.info(
"[%s]: Segments Moved: [%d] Segments Let Alone: [%d]",
Expand Down