DCAwareRoundRobinPolicy (DataStax Enterprise Java Driver

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

All Implemented Interfaces:

LoadBalancingPolicy
```
public class DCAwareRoundRobinPolicy
extends Object
implements LoadBalancingPolicy
```
A data-center aware Round-robin load balancing policy.
This policy provides round-robin queries over the node of the local data center. It also includes in the query plans returned a configurable number of hosts in the remote data centers, but those are always tried after the local nodes. In other words, this policy guarantees that no host in a remote data center will be queried unless no host in the local data center can be reached.
If used with a single data center, this policy is equivalent to the RoundRobinPolicy, but its DC awareness incurs a slight overhead so the latter should be preferred to this policy in that case.

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class DCAwareRoundRobinPolicy.Builder
Helper class to build the policy.

Nested Classes
Modifier and Type	Class and Description
`static class`	`DCAwareRoundRobinPolicy.Builder` Helper class to build the policy.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`static DCAwareRoundRobinPolicy.Builder`	`builder()` Returns a builder to create a new instance.
`void`	`close()` Gets invoked at cluster shutdown.
`HostDistance`	`distance(Host host)` Return the HostDistance for the provided host.
`void`	`init(Cluster cluster, Collection<Host> hosts)` Initialize this load balancing policy.
`boolean`	`isContactPointsMultipleDCs()`
`boolean`	`isUseRemoteHostsForFailover()`
`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

- Method Detail
  - builder
```
public static DCAwareRoundRobinPolicy.Builder builder()
```
    Returns a builder to create a new instance.
    
    Returns:
    
    the builder.
  - 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.
  - isContactPointsMultipleDCs
```
public boolean isContactPointsMultipleDCs()
```
  - isUseRemoteHostsForFailover
```
public boolean isUseRemoteHostsForFailover()
```
  - distance
```
public HostDistance distance(Host host)
```
    Return the HostDistance for the provided host.
    This policy consider nodes in the local datacenter as LOCAL. For each remote datacenter, it considers a configurable number of hosts as REMOTE and the rest is IGNORED.
    To configure how many hosts in each remote datacenter should be considered, see DCAwareRoundRobinPolicy.Builder.withUsedHostsPerRemoteDc(int).
    
    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.
    The returned plan will always try each known host in the local datacenter first, and then, if none of the local host is reachable, will try up to a configurable number of other host per remote datacenter. The order of the local node in the returned query plan will follow a Round-robin algorithm.
    
    Specified by:
    
    newQueryPlan in interface LoadBalancingPolicy
    
    Parameters:
    
    loggedKeyspace - the keyspace currently logged in on for this query.
    
    statement - the query for which to build the plan.
    
    Returns:
    
    a new query plan, i.e. an iterator indicating which host to try first for querying, which one to use as failover, etc...
  - 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 DCAwareRoundRobinPolicy

Nested Class Summary

Method Summary

Methods inherited from class java.lang.Object

Method Detail

builder

init

isContactPointsMultipleDCs

isUseRemoteHostsForFailover

distance

newQueryPlan

onUp

onDown

onAdd

onRemove

close