org.gridgain.grid.cache.affinity
Interface GridCacheAffinity<K>

All Superinterfaces:

Serializable

All Known Implementing Classes:

GridCachePartitionedAffinity, GridCacheReplicatedAffinity

public interface GridCacheAffinity<K>
extends Serializable

Cache key affinity which maps keys to nodes. This interface is utilized for both, replicated and partitioned caches. Cache affinity can be configured for individual caches via GridCacheConfiguration.getAffinity() method.

Whenever a key is given to cache, it is first passed to a pluggable GridCacheAffinityMapper which may potentially map this key to an alternate key which should be used for affinity. The key returned from GridCacheAffinityMapper.affinityKey(Object) method is then passed to partition(Object) method to find out the partition for the key. Then this partition together with all participating nodes are passed to nodes(int, Collection) method which returns a collection of nodes. This collection of nodes is used for node affinity. In REPLICATED cache mode the key will be cached on all returned nodes; generally, all caching nodes participate in caching every key in replicated mode. In PARTITIONED mode, only primary and backup nodes are returned with primary node always in the first position. So if there is 1 backup node, then the returned collection will have 2 nodes in it - primary node in first position, and backup node in second.

For more information about cache affinity and examples refer to GridCacheAffinityMapper and @GridCacheAffinityMapped documentation.

Wiki & Forum:

Wiki
Forum

See Also:

GridCacheAffinityMapped, GridCacheAffinityMapper

Method Summary

Collection<GridRichNode>	nodes(int partition, Collection<GridRichNode> nodes) Gets affinity nodes for a partition.
int	partition(K key) Gets partition number for a given key starting from 0.
int	partitions() Gets total number of partitions available.
void	reset() Resets cache affinity to its initial state.

Method Detail

reset

void reset()

Resets cache affinity to its initial state. This method will be called by the system any time the affinity has been sent to remote node where it has to be reinitialized. If your implementation of affinity function has no initialization logic, leave this method empty.

partitions

int partitions()

Gets total number of partitions available. All caches should always provide correct partition count which should be the same on all participating nodes. Note that partitions should always be numbered from 0 inclusively to N exclusively without any gaps.

Returns:

Total partition count.

partition

int partition(K key)

Gets partition number for a given key starting from 0. Partitioned caches should make sure that keys are about evenly distributed across all partitions from 0 to partition count for best performance.

Note that for fully replicated caches it is possible to segment key sets among different grid node groups. In that case each node group should return a unique partition number. However, unlike partitioned cache, mappings of keys to nodes in replicated caches are constant and a node cannot migrate from one partition to another.

Parameters:

key - Key to get partition for.

Returns:

Partition number for a given key.

nodes

Collection<GridRichNode> nodes(int partition,
                               Collection<GridRichNode> nodes)

Gets affinity nodes for a partition. In case of replicated cache, all returned nodes are updated in the same manner. In case of partitioned cache, the returned list should contain only the primary and back up nodes with primary node being always first.

Parameters:

partition - Partition to get nodes for.

nodes - Nodes to choose from.

Returns:

Affinity nodes for the given partition.