com.sleepycat.je.rep
Enum ReplicatedEnvironment.State

java.lang.Object
  java.lang.Enum<ReplicatedEnvironment.State>
      com.sleepycat.je.rep.ReplicatedEnvironment.State

All Implemented Interfaces:

Serializable, Comparable<ReplicatedEnvironment.State>

Enclosing class:

ReplicatedEnvironment

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

The replication node state determines the operations that the application can perform against its replicated environment. The method ReplicatedEnvironment.getState() returns the current state.

When the first handle to a ReplicatedEnvironment is instantiated and the node is bought up, it always starts out in the DETACHED state and then transitions to the MASTER or REPLICA state before returning from the constructor.

When nodes in the group become unavailable and elections are held, the node may transition between MASTER and REPLICA states.

When the last handle to the environment is closed, the node transitions back to the DETACHED state.

The state transitions for a node can be summarized by the regular expression:

DETACHED [ MASTER | REPLICA | UNKNOWN ]+ DETACHED, with the following caveats:

• A MASTER state never follows a MASTER state, since that would represent a redundant transition.
• Similarly, an UNKNOWN state never follows an UNKNOWN state, since that would be redundant transition.
• A REPLICA state can follow a REPLICA state, as long as this node is not the MASTER.

The initial DETACHED state is internal to the JE HA implementation and is not visible to the application.

Enum Constant Summary

DETACHED
The node is not associated with the group.

MASTER
The node is the unique master of the group and can both read and write to its environment.

REPLICA
The node is a replica that is being updated by the master.

UNKNOWN
The node is not currently in contact with its group, but is actively trying to establish contact and decide upon a master.

Method Summary

boolean	isActive()
boolean	isDetached()
boolean	isMaster()
boolean	isReplica()
boolean	isUnknown()
static ReplicatedEnvironment.State	valueOf(String name) Returns the enum constant of this type with the specified name.
static ReplicatedEnvironment.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

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

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

DETACHED

public static final ReplicatedEnvironment.State DETACHED

The node is not associated with the group. Its handle has been closed. No operations can be performed on the environment when it is in this state.

UNKNOWN

public static final ReplicatedEnvironment.State UNKNOWN

The node is not currently in contact with its group, but is actively trying to establish contact and decide upon a master. While in this state the node is restricted to performing just read operations on its environment. In a functioning group, this state is transitory.

MASTER

public static final ReplicatedEnvironment.State MASTER

The node is the unique master of the group and can both read and write to its environment. When the node transitions to the state, the application running on the node must make provisions to start processing application level write requests in addition to read requests.

REPLICA

public static final ReplicatedEnvironment.State REPLICA

The node is a replica that is being updated by the master. It is restricted to reading its environment. When the node transitions to this state, the application running on the node must make provisions to ensure that it does not write to the environment. It must arrange for all write requests to be routed to the master.

Method Detail

values

public static ReplicatedEnvironment.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 (ReplicatedEnvironment.State c : ReplicatedEnvironment.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 ReplicatedEnvironment.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

isMaster

public final boolean isMaster()

Returns:

true if the node is a Master when in this state

isReplica

public final boolean isReplica()

Returns:

true if the node is a Replica when in this state

isDetached

public final boolean isDetached()

Returns:

true if the node is disconnected from the replication group when in this state.

isUnknown

public final boolean isUnknown()

Returns:

true if the node's state is unknown, and it is attempting to transition to Master or Replica.

isActive

public final boolean isActive()

Returns:

true if the node is currently participating in the group as a Replica or a Master