io.atomix.copycat.server

Enum CopycatServer.State

java.lang.Object

java.lang.Enum<CopycatServer.State>

io.atomix.copycat.server.CopycatServer.State

All Implemented Interfaces:

Serializable, Comparable<CopycatServer.State>

Enclosing class:

CopycatServer

public static enum CopycatServer.State
extends Enum<CopycatServer.State>

Copycat server state types.

States represent the context of the server's internal state machine. Throughout the lifetime of a server, the server will periodically transition between states based on requests, responses, and timeouts.

Author:

Jordan Halterman

Enum Constant Summary

Enum Constants

Enum Constant and Description
CANDIDATE Represents the state of a server attempting to become the leader.
FOLLOWER Represents the state of a server participating in normal log replication.
INACTIVE Represents the state of an inactive server.
LEADER Represents the state of a server which is actively coordinating and replicating logs with other servers.
PASSIVE Represents the state of a server in the process of catching up its log.
RESERVE Represents the state of a server that is a reserve member of the cluster.

Method Summary

Modifier and Type	Method and Description
static CopycatServer.State	valueOf(String name) Returns the enum constant of this type with the specified name.
static CopycatServer.State[]	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

INACTIVE

public static final CopycatServer.State INACTIVE

Represents the state of an inactive server.

All servers start in this state and return to this state when stopped.

RESERVE

public static final CopycatServer.State RESERVE

Represents the state of a server that is a reserve member of the cluster.

Reserve servers only receive notification of leader, term, and configuration changes.

PASSIVE

public static final CopycatServer.State PASSIVE

Represents the state of a server in the process of catching up its log.

Upon successfully joining an existing cluster, the server will transition to the passive state and remain there until the leader determines that the server has caught up enough to be promoted to a full member.

FOLLOWER

public static final CopycatServer.State FOLLOWER

Represents the state of a server participating in normal log replication.

The follower state is a standard Raft state in which the server receives replicated log entries from the leader.

CANDIDATE

public static final CopycatServer.State CANDIDATE

Represents the state of a server attempting to become the leader.

When a server in the follower state fails to receive communication from a valid leader for some time period, the follower will transition to the candidate state. During this period, the candidate requests votes from each of the other servers in the cluster. If the candidate wins the election by receiving votes from a majority of the cluster, it will transition to the leader state.

LEADER

public static final CopycatServer.State LEADER

Represents the state of a server which is actively coordinating and replicating logs with other servers.

Leaders are responsible for handling and replicating writes from clients. Note that more than one leader can exist at any given time, but Raft guarantees that no two leaders will exist for the same Cluster.term().

Method Detail

values

public static CopycatServer.State[] 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 (CopycatServer.State c : CopycatServer.State.values())
    System.out.println(c);

Returns:

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

valueOf

public static CopycatServer.State valueOf(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:

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

NullPointerException - if the argument is null