io.atomix.protocols.raft.session

Enum CommunicationStrategy

java.lang.Object

java.lang.Enum<CommunicationStrategy>

io.atomix.protocols.raft.session.CommunicationStrategy

All Implemented Interfaces:

java.io.Serializable, java.lang.Comparable<CommunicationStrategy>

public enum CommunicationStrategy
extends java.lang.Enum<CommunicationStrategy>

Strategy for selecting nodes to which to connect and submit operations.

Selection strategies prioritize communication with certain servers over others. When the client loses its connection or cluster membership changes, the client will request a list of servers to which the client can connect. The address list should be prioritized.

Enum Constant Summary

Enum Constants

Enum Constant and Description
ANY The ANY selection strategy allows the client to connect to any server in the cluster.
FOLLOWERS The FOLLOWERS selection strategy forces the client to connect only to followers.
LEADER The LEADER selection strategy forces the client to attempt to connect to the cluster's leader.

Method Summary

Modifier and Type	Method and Description
abstract java.util.List<MemberId>	selectConnections(MemberId leader, java.util.List<MemberId> members) Returns a prioritized list of servers to which the client can connect and submit operations.
static CommunicationStrategy	valueOf(java.lang.String name) Returns the enum constant of this type with the specified name.
static CommunicationStrategy[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

compareTo, equals, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

ANY

public static final CommunicationStrategy ANY

The ANY selection strategy allows the client to connect to any server in the cluster. Clients will attempt to connect to a random server, and the client will persist its connection with the first server through which it is able to communicate. If the client becomes disconnected from a server, it will attempt to connect to the next random server again.

LEADER

public static final CommunicationStrategy LEADER

The LEADER selection strategy forces the client to attempt to connect to the cluster's leader. Connecting to the leader means the client's operations are always handled by the first server to receive them. However, clients connected to the leader will not significantly benefit from operations with lower consistency levels, and more clients connected to the leader could mean more load on a single point in the cluster.

If the client is unable to find a leader in the cluster, the client will connect to a random server.

FOLLOWERS

public static final CommunicationStrategy FOLLOWERS

The FOLLOWERS selection strategy forces the client to connect only to followers. Connecting to followers ensures that the leader is not overloaded with direct client requests. This strategy should be used when clients frequently submit operations with lower consistency levels that don't need to be forwarded to the cluster leader. For clients that frequently submit commands or queries with linearizable consistency, the LEADER ConnectionStrategy may be more performant.

Method Detail

values

public static CommunicationStrategy[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (CommunicationStrategy c : CommunicationStrategy.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static CommunicationStrategy valueOf(java.lang.String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

java.lang.IllegalArgumentException - if this enum type has no constant with the specified name

java.lang.NullPointerException - if the argument is null

selectConnections

public abstract java.util.List<MemberId> selectConnections(MemberId leader,
                                                           java.util.List<MemberId> members)

Returns a prioritized list of servers to which the client can connect and submit operations.

The client will iterate the provided MemberId list in order, attempting to connect to each listed server until all servers have been exhausted. Implementations should provide a complete list of servers with which the client can communicate. Limiting the server list only to a single server such as the leader may result in the client failing, such as in the event that no leader exists or the client is partitioned from the leader.

Parameters:

leader - The current cluster leader. The leader may be null if no current leader exists.

members - The full list of available servers. The provided server list is representative of the most recent membership update received by the client. The server list may evolve over time as the structure of the cluster changes.

Returns:

A collection of servers to which the client can connect.