org.apache.pinot.broker.routing.instanceselector.BalancedInstanceSelector Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.pinot.broker.routing.instanceselector;
import java.time.Clock;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.annotation.Nullable;
import org.apache.helix.store.zk.ZkHelixPropertyStore;
import org.apache.helix.zookeeper.datamodel.ZNRecord;
import org.apache.pinot.broker.routing.adaptiveserverselector.AdaptiveServerSelector;
import org.apache.pinot.common.metrics.BrokerMetrics;
import org.apache.pinot.common.utils.HashUtil;
/**
* Instance selector to balance the number of segments served by each selected server instance.
* If AdaptiveServerSelection is enabled, the request is routed to the best available server for a segment
* when it is processed below. This is a best effort approach in distributing the query to all available servers.
* If some servers are performing poorly, they might not end up being picked for any of the segments. For example,
* there's a query for Segments 1 (Seg1), 2 (Seg2) and Seg3). The servers are S1, S2, S3. The algorithm works as
* follows:
* Step1: Process seg1. Fetch server rankings. Pick the best server.
* Step2: Process seg2. Fetch server rankings (could have changed or not since Step 1). Pick the best server.
* Step3: Process seg3. Fetch server rankings (could have changed or not since Step 2). Pick the best server.
*
*
If AdaptiveServerSelection is disabled, the selection algorithm will always evenly distribute the traffic to all
* replicas of each segment, and will try to select different replica id for each segment. The algorithm is very
* light-weight and will do best effort to balance the number of segments served by each selected server instance.
*/
public class BalancedInstanceSelector extends BaseInstanceSelector {
public BalancedInstanceSelector(String tableNameWithType, ZkHelixPropertyStore propertyStore,
BrokerMetrics brokerMetrics, @Nullable AdaptiveServerSelector adaptiveServerSelector, Clock clock) {
super(tableNameWithType, propertyStore, brokerMetrics, adaptiveServerSelector, clock);
}
@Override
Map select(List segments, int requestId, SegmentStates segmentStates,
Map queryOptions) {
Map segmentToSelectedInstanceMap = new HashMap<>(HashUtil.getHashMapCapacity(segments.size()));
if (_adaptiveServerSelector != null) {
for (String segment : segments) {
List candidates = segmentStates.getCandidates(segment);
// NOTE: candidates can be null when there is no enabled instances for the segment, or the instance selector has
// not been updated (we update all components for routing in sequence)
if (candidates == null) {
continue;
}
List candidateInstances = new ArrayList<>(candidates.size());
for (SegmentInstanceCandidate candidate : candidates) {
candidateInstances.add(candidate.getInstance());
}
String selectedInstance = _adaptiveServerSelector.select(candidateInstances);
if (candidates.get(candidateInstances.indexOf(selectedInstance)).isOnline()) {
segmentToSelectedInstanceMap.put(segment, selectedInstance);
}
}
} else {
for (String segment : segments) {
List candidates = segmentStates.getCandidates(segment);
// NOTE: candidates can be null when there is no enabled instances for the segment, or the instance selector has
// not been updated (we update all components for routing in sequence)
if (candidates == null) {
continue;
}
int selectedIdx = requestId++ % candidates.size();
SegmentInstanceCandidate selectedCandidate = candidates.get(selectedIdx);
if (selectedCandidate.isOnline()) {
segmentToSelectedInstanceMap.put(segment, selectedCandidate.getInstance());
}
}
}
return segmentToSelectedInstanceMap;
}
}