聊聊elasticsearch的ElectMasterService
摘要：
序
本文主要研究一下elasticsearch的ElectMasterService
ElectMasterService
elasticsearch-7.0.1/server/src/main/java/org/elasticsearch/discovery/zen/ElectM...
序
本文主要研究一下elasticsearch的ElectMasterService
ElectMasterService
elasticsearch-7.0.1/server/src/main/java/org/elasticsearch/discovery/zen/ElectMasterService.java
public class ElectMasterService {
private static final Logger logger = LogManager.getLogger(ElectMasterService.class);
public static final Setting<Integer> DISCOVERY_ZEN_MINIMUM_MASTER_NODES_SETTING =
Setting.intSetting("discovery.zen.minimum_master_nodes", -1, Property.Dynamic, Property.NodeScope, Property.Deprecated);
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) {
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 {@code null}
* 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
possibleNodes.removeIf(node -> !node.isMasterNode());
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());
}
}
- ElectMasterService的構造器讀取discovery.zen.minimum_master_nodes配置到變數minimumMasterNodes
- ElectMasterService定義了靜態類MasterCandidate，它提供了compare靜態方法用於比較兩個MasterCandidate，它首先對比clusterStateVersion，如果該值相同再進行compareNodes，compareNodes會先判斷下是否masterNode，都不是則對比他們各自的node的id
- electMaster方法首先通過hasEnoughCandidates來確定是否有足夠的candidates，足夠的話則對他們進行排序，最後取第一個作為master返回
ZenDiscovery.findMaster
elasticsearch-7.0.1/server/src/main/java/org/elasticsearch/discovery/zen/ZenDiscovery.java
public class ZenDiscovery extends AbstractLifecycleComponent implements Discovery, PingContextProvider, IncomingClusterStateListener {
//......
private DiscoveryNode findMaster() {
logger.trace("starting to ping");
List<ZenPing.PingResponse> fullPingResponses = pingAndWait(pingTimeout).toList();
if (fullPingResponses == null) {
logger.trace("No full ping responses");
return null;
}
if (logger.isTraceEnabled()) {
StringBuilder sb = new StringBuilder();
if (fullPingResponses.size() == 0) {
sb.append(" {none}");
} else {
for (ZenPing.PingResponse pingResponse : fullPingResponses) {
sb.append("\n\t--> ").append(pingResponse);
}
}
logger.trace("full ping responses:{}", sb);
}
final DiscoveryNode localNode = transportService.getLocalNode();
// add our selves
assert fullPingResponses.stream().map(ZenPing.PingResponse::node)
.filter(n -> n.equals(localNode)).findAny().isPresent() == false;
fullPingResponses.add(new ZenPing.PingResponse(localNode, null, this.clusterState()));
// filter responses
final List<ZenPing.PingResponse> pingResponses = filterPingResponses(fullPingResponses, masterElectionIgnoreNonMasters, logger);
List<DiscoveryNode> activeMasters = new ArrayList<>();
for (ZenPing.PingResponse pingResponse : pingResponses) {
// We can't include the local node in pingMasters list, otherwise we may up electing ourselves without
// any check / verifications from other nodes in ZenDiscover#innerJoinCluster()
if (pingResponse.master() != null && !localNode.equals(pingResponse.master())) {
activeMasters.add(pingResponse.master());
}
}
// nodes discovered during pinging
List<ElectMasterService.MasterCandidate> masterCandidates = new ArrayList<>();
for (ZenPing.PingResponse pingResponse : pingResponses) {
if (pingResponse.node().isMasterNode()) {
masterCandidates.add(new ElectMasterService.MasterCandidate(pingResponse.node(), pingResponse.getClusterStateVersion()));
}
}
if (activeMasters.isEmpty()) {
if (electMaster.hasEnoughCandidates(masterCandidates)) {
final ElectMasterService.MasterCandidate winner = electMaster.electMaster(masterCandidates);
logger.trace("candidate {} won election", winner);
return winner.getNode();
} else {
// if we don't have enough master nodes, we bail, because there are not enough master to elect from
logger.warn("not enough master nodes discovered during pinging (found [{}], but needed [{}]), pinging again",
masterCandidates, electMaster.minimumMasterNodes());
return null;
}
} else {
assert !activeMasters.contains(localNode) :
"local node should never be elected as master when other nodes indicate an active master";
// lets tie break between discovered nodes
return electMaster.tieBreakActiveMasters(activeMasters);
}
}
//......
}
- ZenDiscovery的findMaster方法在activeMasters.isEmpty()時會通過electMaster.electMaster(masterCandidates)來選取winner作為master返回
小結
- ElectMasterService的構造器讀取discovery.zen.minimum_master_nodes配置到變數minimumMasterNodes；ElectMasterService定義了靜態類MasterCandidate，它提供了compare靜態方法用於比較兩個MasterCandidate，它首先對比clusterStateVersion，如果該值相同再進行compareNodes，compareNodes會先判斷下是否masterNode，都不是則對比他們各自的node的id
- electMaster方法首先通過hasEnoughCandidates來確定是否有足夠的candidates，足夠的話則對他們進行排序，最後取第一個作為master返回
- ZenDiscovery的findMaster方法在activeMasters.isEmpty()時會通過electMaster.electMaster(masterCandidates)來選取winner作為master返回