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Two methods need to be implemented:
: returns the "distance" of an host for that balancing policy.
: it is used for each query to find which host to query first, and which hosts to use as failover.
LoadBalancingPolicy is a
and is thus informed of hosts up/down events. For efficiency purposes, the
policy is expected to exclude down hosts from query plans.
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.
Clusterinstance for which the policy is created.
hoststhe initial hosts to use.
The distance of an host influence how much connections are kept to the
). A policy should assign a
LOCAL distance to nodes that are susceptible to be returned first by
newQueryPlan and it is useless for
return hosts to which it assigns an
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.
hostthe host of which to return the distance of.
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
querythe query for which to build a plan.