TokenAwarePolicy (DataStax Java Driver for Apache Cassandra

java.lang.Object
- com.datastax.driver.core.policies.TokenAwarePolicy

All Implemented Interfaces:

ChainableLoadBalancingPolicy, LoadBalancingPolicy
```
public class TokenAwarePolicy
extends Object
implements ChainableLoadBalancingPolicy
```
A wrapper load balancing policy that add token awareness to a child policy.
This policy encapsulates another policy. The resulting policy works in the following way:
- the distance method is inherited from the child policy.
- the iterator return by the newQueryPlan method will first return the LOCAL replicas for the query (based on Statement.getRoutingKey()) if possible (i.e. if the query getRoutingKey method doesn't return null and if Metadata.getReplicas(java.lang.String, java.nio.ByteBuffer) returns a non empty set of replicas for that partition key). If no local replica can be either found or successfully contacted, the rest of the query plan will fallback to one of the child policy.
Do note that only replica for which the child policy distance method returns HostDistance.LOCAL will be considered having priority. For example, if you wrap DCAwareRoundRobinPolicy with this token aware policy, replicas from remote data centers may only be returned after all the host of the local data center.

Constructor Summary

Constructors
Constructor and Description
`TokenAwarePolicy(LoadBalancingPolicy childPolicy)` Creates a new `TokenAware` policy with shuffling of replicas.
`TokenAwarePolicy(LoadBalancingPolicy childPolicy, boolean shuffleReplicas)` Creates a new `TokenAware` policy.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`close()` Gets invoked at cluster shutdown.
`HostDistance`	`distance(Host host)` Return the HostDistance for the provided host.
`LoadBalancingPolicy`	`getChildPolicy()` Returns the child policy.
`void`	`init(Cluster cluster, Collection<Host> hosts)` Initialize this load balancing policy.
`Iterator<Host>`	`newQueryPlan(String loggedKeyspace, Statement statement)` Returns the hosts to use for a new query.
`void`	`onAdd(Host host)` Called when a new node is added to the cluster.
`void`	`onDown(Host host)` Called when a node is determined to be down.
`void`	`onRemove(Host host)` Called when a node is removed from the cluster.
`void`	`onUp(Host host)` Called when a node is determined to be up.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - TokenAwarePolicy
```
public TokenAwarePolicy(LoadBalancingPolicy childPolicy,
                        boolean shuffleReplicas)
```
    Creates a new TokenAware policy.
    
    Parameters:
    
    childPolicy - the load balancing policy to wrap with token awareness.
    
    shuffleReplicas - whether to shuffle the replicas returned by getRoutingKey. Note that setting this parameter to true might decrease the effectiveness of caching (especially at consistency level ONE), since the same row will be retrieved from any replica (instead of only the "primary" replica without shuffling). On the other hand, shuffling will better distribute writes, and can alleviate hotspots caused by "fat" partitions.
  - TokenAwarePolicy
```
public TokenAwarePolicy(LoadBalancingPolicy childPolicy)
```
    Creates a new TokenAware policy with shuffling of replicas.
    
    Parameters:
    
    childPolicy - the load balancing policy to wrap with token awareness.
    
    See Also:
    
    TokenAwarePolicy(LoadBalancingPolicy, boolean)
- Method Detail
  - getChildPolicy
```
public LoadBalancingPolicy getChildPolicy()
```
    Description copied from interface: ChainableLoadBalancingPolicy
    
    Returns the child policy.
    
    Specified by:
    
    getChildPolicy in interface ChainableLoadBalancingPolicy
    
    Returns:
    
    the child policy.
  - init
```
public void init(Cluster cluster,
                 Collection<Host> hosts)
```
    Description copied from interface: LoadBalancingPolicy
    
    Initialize this load balancing policy.
    Note that the driver guarantees that it will call this method exactly once per policy object and will do so before any call to another of the methods of the policy.
    
    Specified by:
    
    init in interface LoadBalancingPolicy
    
    Parameters:
    
    cluster - the Cluster instance for which the policy is created.
    
    hosts - the initial hosts to use.
  - distance
```
public HostDistance distance(Host host)
```
    Return the HostDistance for the provided host.
    
    Specified by:
    
    distance in interface LoadBalancingPolicy
    
    Parameters:
    
    host - the host of which to return the distance of.
    
    Returns:
    
    the HostDistance to host as returned by the wrapped policy.
  - newQueryPlan
```
public Iterator<Host> newQueryPlan(String loggedKeyspace,
                                   Statement statement)
```
    Returns the hosts to use for a new query.
    The returned plan will first return replicas (whose HostDistance for the child policy is LOCAL) for the query if it can determine them (i.e. mainly if statement.getRoutingKey() is not null). Following what it will return the plan of the child policy.
    
    Specified by:
    
    newQueryPlan in interface LoadBalancingPolicy
    
    Parameters:
    
    statement - the query for which to build the plan.
    
    loggedKeyspace - the currently logged keyspace (the one set through either Cluster.connect(String) or by manually doing a USE query) for the session on which this plan need to be built. This can be null if the corresponding session has no keyspace logged in.
    
    Returns:
    
    the new query plan.
  - onUp
```
public void onUp(Host host)
```
    Description copied from interface: LoadBalancingPolicy
    
    Called when a node is determined to be up.
    
    Specified by:
    
    onUp in interface LoadBalancingPolicy
    
    Parameters:
    
    host - the host that has been detected up.
  - onDown
```
public void onDown(Host host)
```
    Description copied from interface: LoadBalancingPolicy
    
    Called when a node is determined to be down.
    
    Specified by:
    
    onDown in interface LoadBalancingPolicy
    
    Parameters:
    
    host - the host that has been detected down.
  - onAdd
```
public void onAdd(Host host)
```
    Description copied from interface: LoadBalancingPolicy
    
    Called when a new node is added to the cluster.
    The newly added node should be considered up.
    
    Specified by:
    
    onAdd in interface LoadBalancingPolicy
    
    Parameters:
    
    host - the host that has been newly added.
  - onRemove
```
public void onRemove(Host host)
```
    Description copied from interface: LoadBalancingPolicy
    
    Called when a node is removed from the cluster.
    
    Specified by:
    
    onRemove in interface LoadBalancingPolicy
    
    Parameters:
    
    host - the removed host.
  - close
```
public void close()
```
    Description copied from interface: LoadBalancingPolicy
    
    Gets invoked at cluster shutdown. This gives the policy the opportunity to perform some cleanup, for instance stop threads that it might have started.
    
    Specified by:
    
    close in interface LoadBalancingPolicy

Class TokenAwarePolicy

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

TokenAwarePolicy

TokenAwarePolicy

Method Detail

getChildPolicy

init

distance

newQueryPlan

onUp

onDown

onAdd

onRemove

close