Package com.datastax.driver.core.policies

Class RoundRobinPolicy

  • All Implemented Interfaces:
    LoadBalancingPolicy
    public class RoundRobinPolicy
extends Object
implements LoadBalancingPolicy
    A Round-robin load balancing policy.

    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 Detail

      • RoundRobinPolicy

        public RoundRobinPolicy()
        Creates a load balancing policy that picks host to query in a round robin fashion (on all the hosts of the Cassandra cluster).

    • Method Detail

      • 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.

        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.

        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 try each known host of the cluster. Upon each call to this method, the ith host of the plans returned will cycle over all the hosts of the cluster in a round-robin fashion.

        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.

      • 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