com.datastax.oss.driver.api.core.loadbalancing.LoadBalancingPolicy Maven / Gradle / Ivy
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package com.datastax.oss.driver.api.core.loadbalancing;
import com.datastax.oss.driver.api.core.metadata.Node;
import com.datastax.oss.driver.api.core.metadata.NodeState;
import com.datastax.oss.driver.api.core.session.Request;
import com.datastax.oss.driver.api.core.session.Session;
import com.datastax.oss.driver.api.core.tracker.RequestTracker;
import edu.umd.cs.findbugs.annotations.NonNull;
import edu.umd.cs.findbugs.annotations.Nullable;
import java.util.Map;
import java.util.Optional;
import java.util.Queue;
import java.util.UUID;
/** Decides which Cassandra nodes to contact for each query. */
public interface LoadBalancingPolicy extends AutoCloseable {
/**
* Returns an optional {@link RequestTracker} to be registered with the session. Registering a
* request tracker allows load-balancing policies to track node latencies in order to pick the
* fastest ones.
*
* This method is invoked only once during session configuration, and before any other methods
* in this interface. Note that at this point, the driver hasn't connected to any node yet.
*
* @since 4.13.0
*/
@NonNull
default Optional getRequestTracker() {
return Optional.empty();
}
/**
* Initializes this policy with the nodes discovered during driver initialization.
*
* This method is guaranteed to be called exactly once per instance, and before any other
* method in this interface except {@link #getRequestTracker()}. At this point, the driver has
* successfully connected to one of the contact points, and performed a first refresh of topology
* information (by default, the contents of {@code system.peers}), to discover other nodes in the
* cluster.
*
*
This method must call {@link DistanceReporter#setDistance(Node, NodeDistance)
* distanceReporter.setDistance} for each provided node (otherwise that node will stay at distance
* {@link NodeDistance#IGNORED IGNORED}, and the driver won't open connections to it). Note that
* the node's {@link Node#getState() state} can be either {@link NodeState#UP UP} (for the
* successful contact point), {@link NodeState#DOWN DOWN} (for contact points that were tried
* unsuccessfully), or {@link NodeState#UNKNOWN UNKNOWN} (for contact points that weren't tried,
* or any other node discovered from the topology refresh). Node states may be updated
* concurrently while this method executes, but if so this policy will get notified after this
* method has returned, through other methods such as {@link #onUp(Node)} or {@link
* #onDown(Node)}.
*
* @param nodes all the nodes that are known to exist in the cluster (regardless of their state)
* at the time of invocation.
* @param distanceReporter an object that will be used by the policy to signal distance changes.
* Implementations will typically store this in a field, since new nodes may get {@link
* #onAdd(Node) added} later and will need to have their distance set (or the policy might
* change distances dynamically over time).
*/
void init(@NonNull Map nodes, @NonNull DistanceReporter distanceReporter);
/**
* Returns the coordinators to use for a new query.
*
* Each new query will call this method, and try the returned nodes sequentially.
*
* @param request the request that is being routed. Note that this can be null for some internal
* uses.
* @param session the session that is executing the request. Note that this can be null for some
* internal uses.
* @return the list of coordinators to try. This must be a concurrent queue; {@link
* java.util.concurrent.ConcurrentLinkedQueue} is a good choice.
*/
@NonNull
Queue newQueryPlan(@Nullable Request request, @Nullable Session session);
/**
* Called when a node is added to the cluster.
*
* The new node will be at distance {@link NodeDistance#IGNORED IGNORED}, and have the state
* {@link NodeState#UNKNOWN UNKNOWN}.
*
*
If this method assigns an active distance to the node, the driver will try to create a
* connection pool to it (resulting in a state change to {@link #onUp(Node) UP} or {@link
* #onDown(Node) DOWN} depending on the outcome).
*
*
If it leaves it at distance {@link NodeDistance#IGNORED IGNORED}, the driver won't attempt
* any connection. The node state will remain unknown, but might be updated later if a topology
* event is received from the cluster.
*
* @see #init(Map, DistanceReporter)
*/
void onAdd(@NonNull Node node);
/** Called when a node is determined to be up. */
void onUp(@NonNull Node node);
/** Called when a node is determined to be down. */
void onDown(@NonNull Node node);
/** Called when a node is removed from the cluster. */
void onRemove(@NonNull Node node);
/** Called when the cluster that this policy is associated with closes. */
@Override
void close();
/** An object that the policy uses to signal decisions it makes about node distances. */
interface DistanceReporter {
void setDistance(@NonNull Node node, @NonNull NodeDistance distance);
}
}