com.datastax.driver.core.policies

Class DCAwareRoundRobinPolicy.Builder

java.lang.Object

com.datastax.driver.core.policies.DCAwareRoundRobinPolicy.Builder

Enclosing class:

DCAwareRoundRobinPolicy

public static class DCAwareRoundRobinPolicy.Builder
extends Object

Helper class to build the policy.

Constructor Summary

Constructors

Constructor and Description
Builder()

Method Summary

Modifier and Type	Method and Description
DCAwareRoundRobinPolicy.Builder	allowRemoteDCsForLocalConsistencyLevel() Allows the policy to return remote hosts when building query plans for queries having consistency level LOCAL_ONE or LOCAL_QUORUM.
DCAwareRoundRobinPolicy	build() Builds the policy configured by this builder.
DCAwareRoundRobinPolicy.Builder	withLocalDc(String localDc) Sets the name of the datacenter that will be considered "local" by the policy.
DCAwareRoundRobinPolicy.Builder	withUsedHostsPerRemoteDc(int usedHostsPerRemoteDc) Sets the number of hosts per remote datacenter that the policy should consider.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Builder

public Builder()

Method Detail

withLocalDc

public DCAwareRoundRobinPolicy.Builder withLocalDc(String localDc)

Sets the name of the datacenter that will be considered "local" by the policy.

This must be the name as known by Cassandra (in other words, the name in that appears in system.peers, or in the output of admin tools like nodetool).

If this method isn't called, the policy will default to the datacenter of the first node connected to. This will always be ok if all the contact points use at Cluster creation are in the local data-center. Otherwise, you should provide the name yourself with this method.

Parameters:

localDc - the name of the datacenter. It should not be null.

Returns:

this builder.

withUsedHostsPerRemoteDc

public DCAwareRoundRobinPolicy.Builder withUsedHostsPerRemoteDc(int usedHostsPerRemoteDc)

Sets the number of hosts per remote datacenter that the policy should consider.

The policy's distance() method will return a HostDistance.REMOTE distance for only usedHostsPerRemoteDc hosts per remote datacenter. Other hosts of the remote datacenters will be ignored (and thus no connections to them will be maintained).

If usedHostsPerRemoteDc > 0, then if for a query no host in the local datacenter can be reached and if the consistency level of the query is not LOCAL_ONE or LOCAL_QUORUM, then up to usedHostsPerRemoteDc hosts per remote datacenter will be tried by the policy as a fallback. By default, no remote host will be used for LOCAL_ONE and LOCAL_QUORUM, since this would change the meaning of the consistency level, somewhat breaking the consistency contract (this can be overridden with allowRemoteDCsForLocalConsistencyLevel()).

If this method isn't called, the policy will default to 0.

Parameters:

usedHostsPerRemoteDc - the number.

Returns:

this builder.

allowRemoteDCsForLocalConsistencyLevel

public DCAwareRoundRobinPolicy.Builder allowRemoteDCsForLocalConsistencyLevel()

Allows the policy to return remote hosts when building query plans for queries having consistency level LOCAL_ONE or LOCAL_QUORUM.

When used in conjunction with usedHostsPerRemoteDc > 0, this overrides the policy of never using remote datacenter nodes for LOCAL_ONE and LOCAL_QUORUM queries. It is however inadvisable to do so in almost all cases, as this would potentially break consistency guarantees and if you are fine with that, it's probably better to use a weaker consistency like ONE, TWO or THREE. As such, this method should generally be avoided; use it only if you know and understand what you do.

Returns:

this builder.

build

public DCAwareRoundRobinPolicy build()

Builds the policy configured by this builder.

Returns:

the policy.