Memcached Notes and summaries (6) a consistent hash distribution algorithm for PHP implementation Memcached

First, create an interface with 3 methods:

Addserver: Add a server to the server list

Removeserver: Removing a server from the server list

Lookup: Find the appropriate server to store data in the current server list

Interface distribute{    // Locate the appropriate server in the current server list store data public    function Lookup ($key);     // add a server to the server list     Public function addserver ($server);     // Remove a server    from the server list  Public function removeserver ($server);}

Then define an interface to convert the string to an integer:

Interface hash{    publicfunction _hash ($str);}

Creating a class Consistenthash inherits the above two interfaces, it has two member variables:

$serverList: List of saved servers

$isSorted: Records whether the server list is already sequenced

Implementation of the Addserver method:

     Public functionAddserver ($server){        $hash=$this->_hash ($server); if(!isset($this->serverlist[$hash])) {            //locate a location on the server list by this hash value            $this->serverlist[$hash] =$server; }        //The list of servers has changed so that it is identified as false        $this->issorted =FALSE; return TRUE; }

Implementation of the Removeserver method:

     Public functionRemoveserver ($server){        $hash=$this->_hash ($server); if(isset($this->serverlist[$hash])) {            unset($this->serverlist[$hash]); }        $this->issorted =FALSE; return TRUE; }

The implementation of the lookup method:

     Public functionLookup$key){        //calculate the hash value of the server        $hash=$this->_hash ($key); //determine if the list of servers is sorted        if(!$this-issorted) {            //reverse order (replace the server list with a counter-clockwise ring)            Krsort($this->serverlist,sort_numeric); $this->issorted =TRUE; }        //traverse the list of servers, locate the appropriate server and return        foreach($this->serverlist as $pos=$server){            if($hash>=$pos)return $server; }        return End($this-serverlist); }

Full code:

<?PHP//Convert a string to an integerInterfacehash{ Public function_hash ($str);}Interfacedistribute{//locate the appropriate server to hold the data in the current server list     Public functionLookup$key); //add a server to the server list     Public functionAddserver ($server); //remove a server from the server list     Public functionRemoveserver ($server);}classConsistenthashImplementsHashdistribute{Private $serverList=Array();//List of saved servers    Private $isSorted=FALSE;//record whether the server list is already sequenced     Public function_hash ($str){        return sprintf('%u ',CRC32($str));//Converts a string to 32 as an unsigned integer    }     Public functionLookup$key){        //calculate the hash value of the server        $hash=$this->_hash ($key); //determine if the list of servers is sorted        if(!$this-issorted) {            //reverse order (replace the server list with a counter-clockwise ring)            Krsort($this->serverlist,sort_numeric); $this->issorted =TRUE; }        //traverse the list of servers, locate the appropriate server and return        foreach($this->serverlist as $pos=$server){            if($hash>=$pos)return $server; }        return End($this-serverlist); }     Public functionAddserver ($server){        $hash=$this->_hash ($server); if(!isset($this->serverlist[$hash])) {            //locate a location on the server list by this hash value            $this->serverlist[$hash] =$server; }        //The list of servers has changed so that it is identified as false        $this->issorted =FALSE; return TRUE; }     Public functionRemoveserver ($server){        $hash=$this->_hash ($server); if(isset($this->serverlist[$hash])) {            unset($this->serverlist[$hash]); }        $this->issorted =FALSE; return TRUE; }}$hashserver=NewConsistenthash ();$hashserver->addserver (' 192.168.1.1 ');$hashserver->addserver (' 192.168.1.2 ');$hashserver->addserver (' 192.168.1.3 ');$hashserver->addserver (' 192.168.1.4 ');$hashserver->addserver (' 192.168.1.5 ');Echo' Save Key1 on server: ',$hashserver->lookup (' Key1 '), ' <br/> ';Echo' Save Key2 on server: ',$hashserver->lookup (' Key2 '), ' <br/> ';Echo' =======================<br/><br/> ';$hashserver->removeserver (' 192.168.1.2 ');Echo' Save Key1 on server: ',$hashserver->lookup (' Key1 '), ' <br/> ';Echo' Save Key2 on server: ',$hashserver->lookup (' Key2 '), ' <br/> ';Echo' =======================<br/><br/> ';$hashserver->addserver (' 192.168.1.6 ');Echo' Save Key1 on server: ',$hashserver->lookup (' Key1 '), ' <br/> ';Echo' Save Key2 on server: ',$hashserver->lookup (' Key2 '), ' <br/> ';Echo' =======================<br/><br/> ';

Output:

Save Key1 on server:192.168.1.2save Key2 on server: 192.168.1.5=======================save Key1 on server
    :192.168.1.3Save Key2 on server: 192.168.1.5=======================save Key1 on server : 192.168.1.6Save Key2 on server: 192.168.1.5=======================

Conclusion: When the server is increased or decreased, the consistent Hash algorithm will only change the storage server with a small portion of the data, thus reducing the data loss situation.

Memcached Notes and summaries (6) a consistent hash distribution algorithm for PHP implementation Memcached