/usr/local/memcached/bin/memcached -d -p 11211 -u memcached -vv >> /var/log/memcached.11211.log 2>&1 /usr/local/memcached/bin/memcached -d -p 11212 -u memcached -vv >> /var/log/memcached.11212.log 2>&1 /usr/local/memcached/bin/memcached -d -p 11213 -u memcached -vv >> /var/log/memcached.11213.log 2>&1 /usr/local/memcached/bin/memcached -d -p 11214 -u memcached -vv >> /var/log/memcached.11214.log 2>&1
2.取模hash算法
php代码
<?php /** * Created by PhpStorm. * User: jmsite.cn * Date: 2019/1/28 * Time: 11:38 */ $memcached = new Memcached(); //设置算法为取模hash $memcached->setOptions( array( Memcached::OPT_DISTRIBUTION => Memcached::DISTRIBUTION_MODULA, //Memcached::OPT_LIBKETAMA_COMPATIBLE => true, Memcached::OPT_REMOVE_FAILED_SERVERS=> true, ) ); //增添效劳器 $memcached->addServer('192.168.75.132', '11211'); $memcached->addServer('192.168.75.132', '11212'); $memcached->addServer('192.168.75.132', '11213'); $memcached->addServer('192.168.75.132', '11214'); //写入12个key for ($i =1;$i <= 12;$i++){ $memcached->set('key_'.$i, 'value_'.$i); }
实行上述代码,检察log
#memcached.11211.log <28 new auto-negotiating client connection 28: Client using the ascii protocol <28 set key_2 0 0 7 >28 STORED <28 set key_3 0 0 7 >28 STORED <28 set key_4 0 0 7 >28 STORED <28 set key_10 0 0 8 >28 STORED <28 quit <28 connection closed. #memcached.11212.log <28 new auto-negotiating client connection 28: Client using the ascii protocol <28 set key_1 0 0 7 >28 STORED <28 set key_6 0 0 7 >28 STORED <28 set key_9 0 0 7 >28 STORED <28 set key_12 0 0 8 >28 STORED <28 quit <28 connection closed. #memcached.11213.log <28 new auto-negotiating client connection 28: Client using the ascii protocol <28 set key_7 0 0 7 >28 STORED <28 set key_8 0 0 7 >28 STORED <28 quit <28 connection closed. #memcached.11214.log <28 new auto-negotiating client connection 28: Client using the ascii protocol <28 set key_5 0 0 7 >28 STORED <28 set key_11 0 0 8 >28 STORED <28 quit <28 connection closed.
检察key的散布
解释掉php代码中的11214//$memcached->addServer('192.168.75.132', '11214');
再次实行php代码
检察key的散布
对照两次key的散布:
key_2和key_10掷中没有更改,一直在11211中,其他10个key由于效劳器的削减掷中发生变化
3.一致性hash算法
php代码
<?php /** * Created by PhpStorm. * User: jmsite.cn * Date: 2019/1/28 * Time: 11:38 */ $memcached = new Memcached(); //设置算法为一致性hash $memcached->setOptions( array( Memcached::OPT_DISTRIBUTION => Memcached::DISTRIBUTION_CONSISTENT, Memcached::OPT_LIBKETAMA_COMPATIBLE => true, Memcached::OPT_REMOVE_FAILED_SERVERS=> true, ) ); //增添效劳器 $memcached->addServer('192.168.75.132', '11211'); $memcached->addServer('192.168.75.132', '11212'); $memcached->addServer('192.168.75.132', '11213'); $memcached->addServer('192.168.75.132', '11214'); //写入12个key for ($i =1;$i <= 12;$i++){ $ret = $memcached->set('key_'.$i, 'value_'.$i); }
实行上述代码,检察log
检察key的散布
解释掉php代码中的11214//$memcached->addServer('192.168.75.132', '11214');
再次实行php代码
检察key的散布
对照两次key的散布:
11211原有的key掷中没有发生变化,新增了key_4
11212原有的key掷中没有发生变化
11213原有的key掷中没有发生变化,新增了key_12
有2个key由于效劳器的削减掷中发生变化
4.对照
取模hash算法削减一台效劳器有10个key掷中发生了变化。
一致性hash算法削减一台效劳器2个key掷中发生了变化。
这里只测试了12个key,模仿的数据量太小致使key散布不均匀,但效劳器削减致使key掷中发生变化和模仿数据量大小无关,而是和hash算法有关,这些测试表现了一致性hash算法的上风,取模hash由于效劳器的削减致使大批key的取模效果发生变化,掷中的效劳器也发生了变化;而一致性hash算法key是固定在一个有2^32-1个节点的hash环上,效劳器削减key在hash环上的位置不会发生变化,仅仅影响削减的那台效劳器上key的掷中,增添效劳器也仅仅影响hash环高低一个位置效劳器的部份key罢了
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