CConsistentHash< Key, HashKey > Class Template Reference

A lightweight implementation of Consistent Hashng algorithm. More...

#include <consistent_hash.hh>

Public Types
typedef Key	key_type
typedef uint32_t	value_type
typedef HashKey< key_type >	hasher

Public Member Functions
value_type	hash (const key_type &key) const
	Get consistent hash result of a key. More...
void	setValue (value_type value, size_t weight=1000)
	Add, remove or modify weight of a value. More...

Detailed Description

template<class Key, template< typename >class HashKey = CHashFn>
class CConsistentHash< Key, HashKey >

A lightweight implementation of Consistent Hashng algorithm.

Consistent Hashing is a technique to map a large number of keys to limited amount of values.
Consider a common use case below:
You have 10 servers to serve for 1 million users, you need to decide which user is served by which server. CConsistentHash can do the mapping easily:

• Each user's ID is a key for CConsistentHash;
• Integer 1 to 10 are values denoting each server;
• Firstly you set weight for every value, which could mean the capability of each server, for example, like this:

  CConsistentHash<UserId> mapping;
  mapping.setValue(1, 1000);
  mapping.setValue(2, 1500);
  mapping.setValue(3, 500);
  // ...

• Then for every user request, get which server it should go to, like this:

  uint32_t serverId = mapping.hash(userId); 

The real power of consistent hashing algorithm is that, when you want to add or remove a server from your servers pool, only a fraction of your users will be redirected to a different server, which could make the impact as small as possible. CConsistentHash makes this operation even easier by using one API setValue only:

• Set a positive weight for a new value to add a new server;
• Change the weight of an existing value to adjust the capability of the server;
• Set weight to 0 for an existing value to remove the server;

  Template Parameters

  Key	Type of keys
  HashKey	Hash function for Key

Member Function Documentation

template<class Key, template< typename >class HashKey = CHashFn>

value_type CConsistentHash< Key, HashKey >::hash ( const key_type &  key ) const

inline

Get consistent hash result of a key.

Parameters

key

A key

Returns

An integer denoting the hash result of key

template<class Key, template< typename >class HashKey = CHashFn>

void CConsistentHash< Key, HashKey >::setValue ( value_type  value, size_t  weight = 1000  )

inline

Add, remove or modify weight of a value.

Parameters

value	An integer denoting a value
weight	New weight of value. If it's 0, value will be removed

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The documentation for this class was generated from the following file:

• consistent_hash.hh