29.4. ConsistentHashFactories
Red Hat JBoss Data Grid offers a pluggable mechanism for selecting the consistent hashing algorithm. It is shipped with four implementations but a custom implementation can also be used.
JBoss Data Grid ships with four ConsistentHashFactory implementations:
DefaultConsistentHashFactory
- keeps segments balanced evenly across all the nodes, however the key mapping is not guaranteed to be same across caches,as this depends on the history of each cache.SyncConsistentHashFactory
- guarantees that the key mapping is the same for each cache, provided the current membership is the same. This has a drawback in that a node joining the cache can cause the existing nodes to also exchange segments, resulting in either additional state transfer traffic, the distribution of the data becoming less even, or both.TopologyAwareConsistentHashFactory
- equivalent ofDefaultConsistentHashFactory
, but with server hinting enabled.TopologyAwareSyncConsistentHashFactory
- equivalent ofSyncConsistentHashFactory
, but with server hinting enabled.
The consistent hash implementation can be selected via the hash configuration:
<hash consistentHashFactory="org.infinispan.distribution.ch.TopologyAwareSyncConsistentHashFactory"/>
This configuration guarantees caches with the same members have the same consistent hash, and if the
machineId
, rackId
, or siteId
attributes are specified in the transport configuration it also spreads backup copies across physical machines/racks/data centers.
It has a potential drawback in that it can move a greater number of segments than necessary during re-balancing. This can be mitigated by using a larger number of segments.
Another potential drawback is that the segments are not distributed as evenly as possible, and actually using a very large number of segments can make the distribution of segments worse.
29.4.1. Implementing a ConsistentHashFactory
A custom
ConsistentHashFactory
must implement the org.infinispan.distribution.ch.ConsistenHashFactory
interface with the following methods (all of which return an implementation of org.infinispan.distribution.ch.ConsistentHash
):
Example 29.1. ConsistentHashFactory Methods
create(Hash hashFunction, int numOwners, int numSegments, List<Address> members,Map<Address, Float> capacityFactors) updateMembers(ConsistentHash baseCH, List<Address> newMembers, Map<Address, Float> capacityFactors) rebalance(ConsistentHash baseCH) union(ConsistentHash ch1, ConsistentHash ch2)
Currently it is not possible to pass custom parameters to
ConsistentHashFactory
implementations.