com.hazelcast.cluster

Enum ClusterState

java.lang.Object

java.lang.Enum<ClusterState>

com.hazelcast.cluster.ClusterState

All Implemented Interfaces:

Serializable, Comparable<ClusterState>

public enum ClusterState
extends Enum<ClusterState>

ClusterState consists several states of the cluster which each state can allow and/or deny specific actions and/or change behaviours of specific actions.

There are 5 states:

1. ACTIVE: Cluster will continue to operate without any restriction.
2. NO_MIGRATION: Migrations (partition rebalancing) and backup replications are not allowed. Cluster will continue to operate without any restriction.
3. FROZEN: New members are not allowed to join, partition table/assignments will be frozen. All other operations are allowed and will operate without any restriction. If some members leave the cluster during it is in FROZEN state, they can join back.
4. PASSIVE: New members are not allowed to join. All operations, except the ones marked with AllowedDuringPassiveState, will be rejected immediately.
5. IN_TRANSITION: Shows that ClusterState is in transition. This is a temporary & intermediate state, not allowed to set explicitly.

By default, cluster will be in ACTIVE state. During split-brain merge process, state of the cluster, that is going to join to the major side, will be changed to FROZEN automatically before merge and will be set to the state of the new cluster after merge.

Since:

3.6

See Also:

Cluster.getClusterState(), Cluster.changeClusterState(ClusterState), NodeState

Enum Constant Summary

Enum Constants

Enum Constant and Description
ACTIVE In ACTIVE state, cluster will continue to operate without any restriction.
FROZEN In FROZEN state of the cluster: New members are not allowed to join, except the members left during FROZEN or PASSIVE state.
IN_TRANSITION Shows that ClusterState is in transition.
NO_MIGRATION In NO_MIGRATION state of the cluster, migrations (partition rebalancing) and backup replications are not allowed.
PASSIVE In PASSIVE state of the cluster: New members are not allowed to join, except the members left during FROZEN or PASSIVE state.

Method Summary

Modifier and Type	Method and Description
boolean	isJoinAllowed() Shows whether new member join is allowed.
boolean	isMigrationAllowed() Shows whether migrations and replications are allowed.
static ClusterState	valueOf(String name) Returns the enum constant of this type with the specified name.
static ClusterState[]	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

ACTIVE

public static final ClusterState ACTIVE

In ACTIVE state, cluster will continue to operate without any restriction. All operations are allowed. This is default state of a cluster.

NO_MIGRATION

public static final ClusterState NO_MIGRATION

In NO_MIGRATION state of the cluster, migrations (partition rebalancing) and backup replications are not allowed.

• When a new member joins, it will not be assigned any partitions until cluster state changes to ACTIVE.
• When a member leaves, backups of primary replicas owned by that member will be promoted to primary. But missing backup replicas will not be created/replicated until cluster state changes to ACTIVE.

Cluster will continue to operate without any restriction. All operations are allowed.

Since:

3.9

FROZEN

public static final ClusterState FROZEN

In FROZEN state of the cluster:

• New members are not allowed to join, except the members left during FROZEN or PASSIVE state. For example, cluster has 3 nodes; A, B and C in FROZEN state. If member B leaves the cluster (either proper shutdown or crash), it will be allowed to re-join to the cluster. But another member D, won't be able to join.
• Partition table/assignments will be frozen. When a member leaves the cluster, its partition assignments (as primary and backup) will remain the same, until either that member re-joins to the cluster or ClusterState changes back to ACTIVE. If that member re-joins in FROZEN, it will own all previous partition assignments as it is. If ClusterState changes to ACTIVE then partition re-balancing process will kick-in and all unassigned partitions will be assigned to active members. It's not allowed to change ClusterState to FROZEN when there are pending migration/replication tasks in the system.
• Nodes continue to stay in NodeState.ACTIVE state when cluster goes into the FROZEN state.
• All other operations except migrations are allowed and will operate without any restriction.

PASSIVE

public static final ClusterState PASSIVE

In PASSIVE state of the cluster:

• New members are not allowed to join, except the members left during FROZEN or PASSIVE state.
*
• Partition table/assignments will be frozen. It's not allowed to change ClusterState to PASSIVE when there are pending migration/replication tasks in the system. If some nodes leave the cluster while cluster is in PASSIVE state, they will be removed from the partition table if cluster state moves back to ACTIVE.
• When cluster state is moved to PASSIVE, node are moved to NodeState.PASSIVE. In this regard, when cluster state moves to another state from PASSIVE, nodes become NodeState.ACTIVE.
• All operations, except the ones marked with AllowedDuringPassiveState, will be rejected immediately.

IN_TRANSITION

public static final ClusterState IN_TRANSITION

Shows that ClusterState is in transition. When a state change transaction is started, ClusterState will be shown as IN_TRANSITION during the transaction lifecycle. After transaction completes, it will be in either new state or its previous state depending on transaction's result.

This is a temporary & intermediate state, not allowed to set explicitly.

• Similar to the FROZEN state, new members are not allowed and migration/replication process will be paused.
• If membership change occurs in the cluster, cluster state transition will fail and will be reverted back to the previous state.

Method Detail

values

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

Returns:

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

valueOf

public static ClusterState 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

isJoinAllowed

public boolean isJoinAllowed()

Shows whether new member join is allowed.

Returns:

true when join is allowed, false otherwise

isMigrationAllowed

public boolean isMigrationAllowed()

Shows whether migrations and replications are allowed.

Returns:

true when migrations and replications are allowed, false otherwise