作者:乐天小散_608 | 来源:互联网 | 2020-07-27 21:50
1.开启4个Memcached服务模拟集群usrlocalmemcachedbinmemcached-d-p11211-umemcached-vv>>varlogmemcached.11211.log2
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
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++){
$memcached->set(&#39;key_&#39;.$i, &#39;value_&#39;.$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
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
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(&#39;192.168.75.132&#39;, &#39;11211&#39;);
$memcached->addServer(&#39;192.168.75.132&#39;, &#39;11212&#39;);
$memcached->addServer(&#39;192.168.75.132&#39;, &#39;11213&#39;);
$memcached->addServer(&#39;192.168.75.132&#39;, &#39;11214&#39;);
//写入12个key
for ($i =1;$i <= 12;$i++){
$ret = $memcached->set(&#39;key_&#39;.$i, &#39;value_&#39;.$i);
}
执行上述代码,查看log
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
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