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* Licensed to Elasticsearch under one or more contributor
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* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.discovery.zen;
import com.carrotsearch.hppc.ObjectContainer;
import org.apache.lucene.util.CollectionUtil;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.node.DiscoveryNode;
import org.elasticsearch.common.component.AbstractComponent;
import org.elasticsearch.common.settings.Setting;
import org.elasticsearch.common.settings.Setting.Property;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.util.CollectionUtils;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;
public class ElectMasterService extends AbstractComponent {
public static final Setting<Integer> DISCOVERY_ZEN_MINIMUM_MASTER_NODES_SETTING =
Setting.intSetting("discovery.zen.minimum_master_nodes", -1, Property.Dynamic, Property.NodeScope);
private volatile int minimumMasterNodes;
/**
* a class to encapsulate all the information about a candidate in a master election
* that is needed to decided which of the candidates should win
*/
public static class MasterCandidate {
public static final long UNRECOVERED_CLUSTER_VERSION = -1;
final DiscoveryNode node;
final long clusterStateVersion;
public MasterCandidate(DiscoveryNode node, long clusterStateVersion) {
Objects.requireNonNull(node);
assert clusterStateVersion >= -1 : "got: " + clusterStateVersion;
assert node.isMasterNode();
this.node = node;
this.clusterStateVersion = clusterStateVersion;
}
public DiscoveryNode getNode() {
return node;
}
public long getClusterStateVersion() {
return clusterStateVersion;
}
@Override
public String toString() {
return "Candidate{" +
"node=" + node +
", clusterStateVersion=" + clusterStateVersion +
'}';
}
/**
* compares two candidates to indicate which the a better master.
* A higher cluster state version is better
*
* @return -1 if c1 is a batter candidate, 1 if c2.
*/
public static int compare(MasterCandidate c1, MasterCandidate c2) {
// we explicitly swap c1 and c2 here. the code expects "better" is lower in a sorted
// list, so if c2 has a higher cluster state version, it needs to come first.
int ret = Long.compare(c2.clusterStateVersion, c1.clusterStateVersion);
if (ret == 0) {
ret = compareNodes(c1.getNode(), c2.getNode());
}
return ret;
}
}
public ElectMasterService(Settings settings) {
super(settings);
this.minimumMasterNodes = DISCOVERY_ZEN_MINIMUM_MASTER_NODES_SETTING.get(settings);
logger.debug("using minimum_master_nodes [{}]", minimumMasterNodes);
}
public void minimumMasterNodes(int minimumMasterNodes) {
this.minimumMasterNodes = minimumMasterNodes;
}
public int minimumMasterNodes() {
return minimumMasterNodes;
}
public int countMasterNodes(Iterable<DiscoveryNode> nodes) {
int count = 0;
for (DiscoveryNode node : nodes) {
if (node.isMasterNode()) {
count++;
}
}
return count;
}
public boolean hasEnoughCandidates(Collection<MasterCandidate> candidates) {
if (candidates.isEmpty()) {
return false;
}
if (minimumMasterNodes < 1) {
return true;
}
assert candidates.stream().map(MasterCandidate::getNode).collect(Collectors.toSet()).size() == candidates.size() :
"duplicates ahead: " + candidates;
return candidates.size() >= minimumMasterNodes;
}
/**
* Elects a new master out of the possible nodes, returning it. Returns <tt>null</tt>
* if no master has been elected.
*/
public MasterCandidate electMaster(Collection<MasterCandidate> candidates) {
assert hasEnoughCandidates(candidates);
List<MasterCandidate> sortedCandidates = new ArrayList<>(candidates);
sortedCandidates.sort(MasterCandidate::compare);
return sortedCandidates.get(0);
}
/** selects the best active master to join, where multiple are discovered */
public DiscoveryNode tieBreakActiveMasters(Collection<DiscoveryNode> activeMasters) {
return activeMasters.stream().min(ElectMasterService::compareNodes).get();
}
public boolean hasEnoughMasterNodes(Iterable<DiscoveryNode> nodes) {
final int count = countMasterNodes(nodes);
return count > 0 && (minimumMasterNodes < 0 || count >= minimumMasterNodes);
}
public boolean hasTooManyMasterNodes(Iterable<DiscoveryNode> nodes) {
final int count = countMasterNodes(nodes);
return count > 1 && minimumMasterNodes <= count / 2;
}
public void logMinimumMasterNodesWarningIfNecessary(ClusterState oldState, ClusterState newState) {
// check if min_master_nodes setting is too low and log warning
if (hasTooManyMasterNodes(oldState.nodes()) == false && hasTooManyMasterNodes(newState.nodes())) {
logger.warn("value for setting \"{}\" is too low. This can result in data loss! Please set it to at least a quorum of master-" +
"eligible nodes (current value: [{}], total number of master-eligible nodes used for publishing in this round: [{}])",
ElectMasterService.DISCOVERY_ZEN_MINIMUM_MASTER_NODES_SETTING.getKey(), minimumMasterNodes(),
newState.getNodes().getMasterNodes().size());
}
}
/**
* Returns the given nodes sorted by likelihood of being elected as master, most likely first.
* Non-master nodes are not removed but are rather put in the end
*/
static List<DiscoveryNode> sortByMasterLikelihood(Iterable<DiscoveryNode> nodes) {
ArrayList<DiscoveryNode> sortedNodes = CollectionUtils.iterableAsArrayList(nodes);
CollectionUtil.introSort(sortedNodes, ElectMasterService::compareNodes);
return sortedNodes;
}
/**
* Returns a list of the next possible masters.
*/
public DiscoveryNode[] nextPossibleMasters(ObjectContainer<DiscoveryNode> nodes, int numberOfPossibleMasters) {
List<DiscoveryNode> sortedNodes = sortedMasterNodes(Arrays.asList(nodes.toArray(DiscoveryNode.class)));
if (sortedNodes == null) {
return new DiscoveryNode[0];
}
List<DiscoveryNode> nextPossibleMasters = new ArrayList<>(numberOfPossibleMasters);
int counter = 0;
for (DiscoveryNode nextPossibleMaster : sortedNodes) {
if (++counter >= numberOfPossibleMasters) {
break;
}
nextPossibleMasters.add(nextPossibleMaster);
}
return nextPossibleMasters.toArray(new DiscoveryNode[nextPossibleMasters.size()]);
}
private List<DiscoveryNode> sortedMasterNodes(Iterable<DiscoveryNode> nodes) {
List<DiscoveryNode> possibleNodes = CollectionUtils.iterableAsArrayList(nodes);
if (possibleNodes.isEmpty()) {
return null;
}
// clean non master nodes
for (Iterator<DiscoveryNode> it = possibleNodes.iterator(); it.hasNext(); ) {
DiscoveryNode node = it.next();
if (!node.isMasterNode()) {
it.remove();
}
}
CollectionUtil.introSort(possibleNodes, ElectMasterService::compareNodes);
return possibleNodes;
}
/** master nodes go before other nodes, with a secondary sort by id **/
private static int compareNodes(DiscoveryNode o1, DiscoveryNode o2) {
if (o1.isMasterNode() && !o2.isMasterNode()) {
return -1;
}
if (!o1.isMasterNode() && o2.isMasterNode()) {
return 1;
}
return o1.getId().compareTo(o2.getId());
}
}