1.开启4个Memcached服务模拟集群
/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,
)
);
//添加服务器
$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_'.$i);
}执行上述代码，查看log
#memcached.11211.log <28 new auto-negotiating client connection 28: Client using the ascii protocol <28 set key_2 0 0 7 >28 STORED <28 set key_3 0 0 7 >28 STORED <28 set key_4 0 0 7 >28 STORED <28 set key_10 0 0 8 >28 STORED <28 quit <28 connection closed. #memcached.11212.log <28 new auto-negotiating client connection 28: Client using the ascii protocol <28 set key_1 0 0 7 >28 STORED <28 set key_6 0 0 7 >28 STORED <28 set key_9 0 0 7 >28 STORED <28 set key_12 0 0 8 >28 STORED <28 quit <28 connection closed. #memcached.11213.log <28 new auto-negotiating client connection 28: Client using the ascii protocol <28 set key_7 0 0 7 >28 STORED <28 set key_8 0 0 7 >28 STORED <28 quit <28 connection closed. #memcached.11214.log <28 new auto-negotiating client connection 28: Client using the ascii protocol <28 set key_5 0 0 7 >28 STORED <28 set key_11 0 0 8 >28 STORED <28 quit <28 connection closed.
查看key的分布
注释掉php代码中的11214//$memcached->addServer('192.168.75.132', '11214');
再次执行php代码
查看key的分布
对比两次key的分布：
key_2和key_10命中没有变动，始终在11211中，其他10个key因为服务器的减少命中发生变化
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,
)
);
//添加服务器
$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_'.$i);
}执行上述代码，查看log
查看key的分布
注释掉php代码中的11214//$memcached->addServer('192.168.75.132', '11214');
再次执行php代码
查看key的分布
对比两次key的分布：
11211原有的key命中没有发生变化，新增了key_4
11212原有的key命中没有发生变化
11213原有的key命中没有发生变化，新增了key_12
有2个key因为服务器的减少命中发生变化
4.对比
取模hash算法减少一台服务器有10个key命中发生了变化。
一致性hash算法减少一台服务器2个key命中发生了变化。
这里只测试了12个key，模拟的数据量太小导致key分布不均匀，但服务器减少导致key命中发生变化和模拟数据量大小无关，而是和hash算法有关，这些测试体现了一致性hash算法的优势，取模hash因为服务器的减少导致大量key的取模结果发生变化，命中的服务器也发生了变化；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，服务器减少key在hash环上的位置不会发生变化，仅仅影响减少的那台服务器上key的命中，增加服务器也仅仅影响hash环上下一个位置服务器的部分key而已
以上是PHP取模hash和一致性hash操作Memcached分布式集群的详细内容。更多信息请关注PHP中文网其他相关文章！
