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Docs: clarify cluster state handling

This commit is contained in:
Igor Motov 2015-05-04 17:00:36 -04:00
parent eabeae980b
commit bd453db411
1 changed files with 27 additions and 0 deletions
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27
src/main/java/org/elasticsearch/cluster/ClusterState.java
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@ -33,6 +33,7 @@ import org.elasticsearch.cluster.node.DiscoveryNode;
import org.elasticsearch.cluster.node.DiscoveryNodes; import org.elasticsearch.cluster.node.DiscoveryNodes;
import org.elasticsearch.cluster.routing.*; import org.elasticsearch.cluster.routing.*;
import org.elasticsearch.cluster.routing.allocation.RoutingAllocation; import org.elasticsearch.cluster.routing.allocation.RoutingAllocation;
import org.elasticsearch.cluster.service.InternalClusterService;
import org.elasticsearch.common.Nullable; import org.elasticsearch.common.Nullable;
import org.elasticsearch.common.Strings; import org.elasticsearch.common.Strings;
import org.elasticsearch.common.collect.ImmutableOpenMap; import org.elasticsearch.common.collect.ImmutableOpenMap;
@ -46,6 +47,10 @@ import org.elasticsearch.common.xcontent.ToXContent;
import org.elasticsearch.common.xcontent.XContentBuilder; import org.elasticsearch.common.xcontent.XContentBuilder;
import org.elasticsearch.common.xcontent.XContentFactory; import org.elasticsearch.common.xcontent.XContentFactory;
import org.elasticsearch.common.xcontent.XContentParser; import org.elasticsearch.common.xcontent.XContentParser;
import org.elasticsearch.discovery.Discovery;
import org.elasticsearch.discovery.DiscoveryService;
import org.elasticsearch.discovery.local.LocalDiscovery;
import org.elasticsearch.discovery.zen.publish.PublishClusterStateAction;
import java.io.IOException; import java.io.IOException;
import java.util.EnumSet; import java.util.EnumSet;
@ -54,7 +59,29 @@ import java.util.Locale;
import java.util.Map; import java.util.Map;
/** /**
* Represents the current state of the cluster.
* *
* The cluster state object is immutable with an
* exception of the {@link RoutingNodes} structure, which is built on demand from the {@link RoutingTable},
* and cluster state {@link #status}, which is updated during cluster state publishing and applying
* processing. The cluster state can be updated only on the master node. All updates are performed by on a
* single thread and controlled by the {@link InternalClusterService}. After every update the
* {@link DiscoveryService#publish} method publishes new version of the cluster state to all other nodes in the
* cluster. The actual publishing mechanism is delegated to the {@link Discovery#publish} method and depends on
* the type of discovery. For example, for local discovery it is implemented by the {@link LocalDiscovery#publish}
* method. In the Zen Discovery it is handled in the {@link PublishClusterStateAction#publish} method. The
* publishing mechanism can be overridden by other discovery.
*
* The cluster state implements the {@link Diffable} interface in order to support publishing of cluster state
* differences instead of the entire state on each change. The publishing mechanism should only send differences
* to a node if this node was present in the previous version of the cluster state. If a node is not present was
* not present in the previous version of the cluster state, such node is unlikely to have the previous cluster
* state version and should be sent a complete version. In order to make sure that the differences are applied to
* correct version of the cluster state, each cluster state version update generates {@link #uuid} that uniquely
* identifies this version of the state. This uuid is verified by the {@link ClusterStateDiff#apply} method to
* makes sure that the correct diffs are applied. If uuids don’t match, the {@link ClusterStateDiff#apply} method
* throws the {@link IncompatibleClusterStateVersionException}, which should cause the publishing mechanism to send
* a full version of the cluster state to the node on which this exception was thrown.
*/ */
public class ClusterState implements ToXContent, Diffable<ClusterState> { public class ClusterState implements ToXContent, Diffable<ClusterState> {