TokenAwarePolicy (Java Driver for Scylla and 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 adds 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 returned by the newQueryPlan method will first return the LOCAL replicas for the query if possible (i.e. if the query's routing key is not null and if the set of replicas for that partition key is not empty). If no local replica can be either found or successfully contacted, the rest of the query plan will fallback to the child policy's one.
The exact order in which local replicas are returned is dictated by the strategy provided at instantiation.
Do note that only replicas for which the child policy's distance method returns 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 hosts of the local data center.

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class TokenAwarePolicy.ReplicaOrdering
Strategies for replica ordering.

Nested Classes
Modifier and Type	Class and Description
`static class`	`TokenAwarePolicy.ReplicaOrdering` Strategies for replica ordering.

Constructor Summary

Constructors
Constructor and Description
`TokenAwarePolicy(LoadBalancingPolicy childPolicy)` Creates a new `TokenAware` policy with `RANDOM` replica ordering.
`TokenAwarePolicy(LoadBalancingPolicy childPolicy, boolean shuffleReplicas)` Deprecated. Use `TokenAwarePolicy(LoadBalancingPolicy, ReplicaOrdering)` instead. This constructor will be removed in the next major release.
`TokenAwarePolicy(LoadBalancingPolicy childPolicy, TokenAwarePolicy.ReplicaOrdering replicaOrdering)` 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)` Returns the distance assigned by this policy to 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,
                        TokenAwarePolicy.ReplicaOrdering replicaOrdering)
```
    Creates a new TokenAware policy.
    
    Parameters:
    
    childPolicy - the load balancing policy to wrap with token awareness.
    
    replicaOrdering - the strategy to use to order replicas.
  - TokenAwarePolicy
```
@Deprecated
public TokenAwarePolicy(LoadBalancingPolicy childPolicy,
                                    boolean shuffleReplicas)
```
    Deprecated. Use TokenAwarePolicy(LoadBalancingPolicy, ReplicaOrdering) instead. This constructor will be removed in the next major release.
    
    Creates a new TokenAware policy.
    
    Parameters:
    
    childPolicy - the load balancing policy to wrap with token awareness.
    
    shuffleReplicas - whether or not to shuffle the replicas. If true, then the RANDOM strategy will be used, otherwise the TOPOLOGICAL one will be used.
  - TokenAwarePolicy
```
public TokenAwarePolicy(LoadBalancingPolicy childPolicy)
```
    Creates a new TokenAware policy with RANDOM replica ordering.
    
    Parameters:
    
    childPolicy - the load balancing policy to wrap with token awareness.
- 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)
```
    Returns the distance assigned by this policy to the provided host.
    The distance of an host influence how much connections are kept to the node (see HostDistance). A policy should assign a LOCAL distance to nodes that are susceptible to be returned first by newQueryPlan and it is useless for newQueryPlan to return hosts to which it assigns an IGNORED distance.
    The host distance is primarily used to prevent keeping too many connections to host in remote datacenters when the policy itself always picks host in the local datacenter first.
    This implementation always returns distances as reported by the wrapped policy.
    
    Specified by:
    
    distance in interface LoadBalancingPolicy
    
    Parameters:
    
    host - the host of which to return the distance of.
    
    Returns:
    
    the HostDistance to host.
  - newQueryPlan
```
public Iterator<Host> newQueryPlan(String loggedKeyspace,
                                   Statement statement)
```
    Returns the hosts to use for a new query.
    Each new query will call this method. The first host in the result will then be used to perform the query. In the event of a connection problem (the queried host is down or appear to be so), the next host will be used. If all hosts of the returned Iterator are down, the query will fail.
    The returned plan will first return local replicas for the query (i.e. replicas whose distance according to the child policy is LOCAL), if it can determine them (i.e. mainly if the statement's routing key is not null), and ordered according to the ordering strategy specified at instantiation; following what it will return the rest of the child policy's original query plan.
    
    Specified by:
    
    newQueryPlan in interface LoadBalancingPolicy
    
    Parameters:
    
    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.
    
    statement - the query for which to build a plan.
    
    Returns:
    
    an iterator of Host. The query is tried against the hosts returned by this iterator in order, until the query has been sent successfully to one of the host.
  - 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

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

TokenAwarePolicy

TokenAwarePolicy

TokenAwarePolicy

Method Detail

getChildPolicy

init

distance

newQueryPlan

onUp

onDown

onAdd

onRemove

close