org.neo4j.kernel.ha.com.master

Class SlavePriorities

java.lang.Object

org.neo4j.kernel.ha.com.master.SlavePriorities

public abstract class SlavePriorities
extends Object

Factory for common SlavePriority implementations.

Author:

Mattias Persson

Method Summary

Modifier and Type	Method and Description
static SlavePriority	fixedAscending()
static SlavePriority	fixedDescending()
static SlavePriority	givenOrder()
static SlavePriority	roundRobin()

Methods inherited from class java.lang.Object

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

Method Detail

givenOrder

public static SlavePriority givenOrder()

Returns:

SlavePriority which returns the slaves in the order that they are given in the slaves array.

roundRobin

public static SlavePriority roundRobin()

Returns:

SlavePriority which returns the slaves in a round robin fashion, more precisely the start index in the array increments with each prioritization, ordered by server id in ascending.

fixedDescending

public static SlavePriority fixedDescending()

Returns:

SlavePriority which returns the slaves in the same fixed order sorted by server id in descending order.

fixedAscending

public static SlavePriority fixedAscending()

Returns:

SlavePriority which returns the slaves in the same fixed order sorted by server id in ascending order. This is generally preferrable to fixedDescending(), because this aligns with the tie-breaker aspect of the lowest server id becoming master.

Eg. if you want to ensure that failover most likely will happen in a specific datacenter, you would place low-id instances in that datacenter and choose this strategy. That way, most of the time the most up-to-date instance will be in this data center, and if there is a tie, the tie-break will also end up electing a master in the same data center.

This is in contrast to fixedDescending(), where a high-id server is likely to be most up-to-date if the master fails, but a low-id server is likely to be elected if there is a tie. This makes the two scenarios consistently choose a low-id server as the new master.