org.aredis.cache

Class ConsistentKeyHasher

java.lang.Object

org.aredis.cache.ConsistentKeyHasher

All Implemented Interfaces:

KeyHasher

public class ConsistentKeyHasher
extends Object
implements KeyHasher

Consistent Hashing Algorithm derived from the one in SpyMemcached memcached client. Essentially a number of hashcodes are generated for each server by adding numeric suffixes to each server's connection string and generating the hashcode when this Key Hasher is created. When a key is to be assigned the nearest hashcode greater than the hashcode of the key is determined whose connection is active. (The server hashcodes are treated as points on a circle. So if the there is no greater hashcode the smallest server hashcode is used) The corresponding Connection Index is used. This algorithm re-destributes keys uniformly when a new server is added or removed to the Sharded Set of servers.

Author:

suresh

Constructor Summary

Constructors

Constructor and Description
ConsistentKeyHasher(AsyncRedisConnection[] pconnections) Creates a Consistent Key Hasher with 180 hashes per connection and CRC_HASH as the Hash Algorithm.
ConsistentKeyHasher(AsyncRedisConnection[] pconnections, int phashesPerConnection, HashAlgorithm phashAlg) Creates a Consistent Key Hasher.

Method Summary

Methods

Modifier and Type	Method and Description
int	getConnectionIndex(String key, AsyncRedisConnection[] pconnections, boolean useOnlyActive) Returns the connection index for a key

Methods inherited from class java.lang.Object

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

Constructor Detail

ConsistentKeyHasher

public ConsistentKeyHasher(AsyncRedisConnection[] pconnections,
                   int phashesPerConnection,
                   HashAlgorithm phashAlg)

Creates a Consistent Key Hasher.

Parameters:

pconnections - connections to pick one from

phashesPerConnection - Number of Hashcodes to generate for each connection

phashAlg - Hash Algorithm to generate the hash codes of the key and the servers

ConsistentKeyHasher

public ConsistentKeyHasher(AsyncRedisConnection[] pconnections)

Creates a Consistent Key Hasher with 180 hashes per connection and CRC_HASH as the Hash Algorithm.

Parameters:

pconnections - connections to pick one from

Method Detail

getConnectionIndex

public int getConnectionIndex(String key,
                     AsyncRedisConnection[] pconnections,
                     boolean useOnlyActive)

Description copied from interface: KeyHasher

Returns the connection index for a key

Specified by:

getConnectionIndex in interface KeyHasher

Parameters:

key - key to assign the connection index

pconnections - Connections to pick from

useOnlyActive - True if only active connections are to be picked. Usually true is passed by ShardedAsyncRedisClient.

Returns:

connection index of connection to use