com.datastax.driver.core.policies

Enum TokenAwarePolicy.ReplicaOrdering

java.lang.Object

java.lang.Enum<TokenAwarePolicy.ReplicaOrdering>

com.datastax.driver.core.policies.TokenAwarePolicy.ReplicaOrdering

All Implemented Interfaces:

Serializable, Comparable<TokenAwarePolicy.ReplicaOrdering>

Enclosing class:

TokenAwarePolicy

public static enum TokenAwarePolicy.ReplicaOrdering
extends Enum<TokenAwarePolicy.ReplicaOrdering>

Strategies for replica ordering.

Enum Constant Summary

Enum Constants

Enum Constant and Description
NEUTRAL Return the replicas in the exact same order in which they appear in the child policy's query plan.
RANDOM Return replicas in a different, random order for each query plan.
TOPOLOGICAL Order replicas by token ring topology, i.e.

Method Summary

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

TOPOLOGICAL

public static final TokenAwarePolicy.ReplicaOrdering TOPOLOGICAL

Order replicas by token ring topology, i.e. always return the "primary" replica first, then the second, etc., according to the placement of replicas around the token ring.

This strategy is the only one guaranteed to order replicas in a deterministic and constant way. This increases the effectiveness of server-side row caching (especially at consistency level ONE), but is more heavily impacted by hotspots, since the primary replica is always tried first.

RANDOM

public static final TokenAwarePolicy.ReplicaOrdering RANDOM

Return replicas in a different, random order for each query plan. This is the default strategy.

This strategy fans out writes and thus can alleviate hotspots caused by "fat" partitions, but its randomness makes server-side caching less efficient.

NEUTRAL

public static final TokenAwarePolicy.ReplicaOrdering NEUTRAL

Return the replicas in the exact same order in which they appear in the child policy's query plan.

This is the only strategy that fully respects the child policy's replica ordering. Use it when it is important to keep that order intact (e.g. when using the LatencyAwarePolicy).

Method Detail

values

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

Returns:

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

valueOf

public static TokenAwarePolicy.ReplicaOrdering 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