Interface ILoadBalancingPolicy
The policy that decides which Cassandra hosts to contact for each new query. For efficiency purposes, the policy is expected to exclude down hosts from query plans.
Namespace: Cassandra
Assembly: Cassandra.dll
Syntax
public interface ILoadBalancingPolicyMethods
Distance(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.
Declaration
HostDistance Distance(Host host)Parameters
| Type | Name | Description |
|---|---|---|
| Host | host | the host of which to return the distance of. |
Returns
| Type | Description |
|---|---|
| HostDistance | the HostDistance to |
Initialize(ICluster)
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.
Declaration
void Initialize(ICluster cluster)Parameters
| Type | Name | Description |
|---|---|---|
| ICluster | cluster | The information about the session instance for which the policy is created. |
NewQueryPlan(string, IStatement)
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.
Declaration
IEnumerable<Host> NewQueryPlan(string keyspace, IStatement query)Parameters
| Type | Name | Description |
|---|---|---|
| string | keyspace | Keyspace on which the query is going to be executed, it can be null. |
| IStatement | query | The query for which to build a plan, it can be null. |
Returns
| Type | Description |
|---|---|
| IEnumerable<Host> | 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. |