public class RoundRobinPolicy extends Object implements LoadBalancingPolicy
This policy queries nodes in a round-robin fashion. For a given query, if an host fail, the next one (following the round-robin order) is tried, until all hosts have been tried.
This policy is not datacenter aware and will include every known Cassandra host in its round
robin algorithm. If you use multiple datacenter this will be inefficient and you will want to use
the DCAwareRoundRobinPolicy
load balancing policy instead.
Constructor and Description |
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RoundRobinPolicy()
Creates a load balancing policy that picks host to query in a round robin fashion (on all the
hosts of the Cassandra cluster).
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Modifier and Type | Method and Description |
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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.
|
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.
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public RoundRobinPolicy()
public void init(Cluster cluster, Collection<Host> hosts)
LoadBalancingPolicy
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.
init
in interface LoadBalancingPolicy
cluster
- the Cluster
instance for which the policy is created.hosts
- the initial hosts to use.public HostDistance distance(Host host)
This policy consider all nodes as local. This is generally the right thing to do in a single
datacenter deployment. If you use multiple datacenter, see DCAwareRoundRobinPolicy
instead.
distance
in interface LoadBalancingPolicy
host
- the host of which to return the distance of.host
.public Iterator<Host> newQueryPlan(String loggedKeyspace, Statement statement)
The returned plan will try each known host of the cluster. Upon each call to this method,
the i
th host of the plans returned will cycle over all the hosts of the cluster in a
round-robin fashion.
newQueryPlan
in interface LoadBalancingPolicy
loggedKeyspace
- the keyspace currently logged in on for this query.statement
- the query for which to build the plan.public void onUp(Host host)
LoadBalancingPolicy
onUp
in interface LoadBalancingPolicy
host
- the host that has been detected up.public void onDown(Host host)
LoadBalancingPolicy
onDown
in interface LoadBalancingPolicy
host
- the host that has been detected down.public void onAdd(Host host)
LoadBalancingPolicy
The newly added node should be considered up.
onAdd
in interface LoadBalancingPolicy
host
- the host that has been newly added.public void onRemove(Host host)
LoadBalancingPolicy
onRemove
in interface LoadBalancingPolicy
host
- the removed host.public void close()
LoadBalancingPolicy
This gives the policy the opportunity to perform some cleanup, for instance stop threads that it might have started.
close
in interface LoadBalancingPolicy
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