php生成唯一uid的解决方法详解
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一、生成唯一uuid
二、生成唯一uid
三、生成唯一uid的正确方法
一、生成唯一uuid
看到某些人会用uuid去代替用户的uid
从代码中可以看出,通过unique生成一个以毫秒级时间戳为前缀的字符后md5加密
再通过分隔符进行分割后得到uuid
这种方式虽然极大程度的避免了uid的重复
但是生成的uid太长,足足36个字符,而且是混杂英文和数字符号的,可读性很差
而一般的uid中都是纯数值组成的
function generateUUid($strtoupper = false){ $charid = call_user_func($strtoupper ? 'strtoupper' : 'strtolower', md5(uniqid(microtime(true), true))); $hyphen = chr(45); $uuid = substr($charid, 0, 8) . $hyphen . substr($charid, 8, 4) . $hyphen . substr($charid, 12, 4) . $hyphen . substr($charid, 16, 4) . $hyphen . substr($charid, 20, 12); return $uuid;} //结果:37f14a07-cb18-2e54-4e40-da1e2fa0456d
二、生成唯一uid
由于一般正常的uid都是纯数值型的
而要保证唯一性,必然要跟时间戳有关系,因此有了以下代码
为了尽可能的在同一秒中注册人数的uid不同,将时间戳进行打乱随机排序,也不失为一个好办法
但是这种缺点就是,uid长度是固定的,无法进行改变,虽然呢,打乱字符是一个很好的解决重复的方式
但是事情无绝对,如果真的因为随机碰撞导致的uid相同该如何
为了更保险起见,必然还是要走一次数据库的查询
大大增加了数据库的I/O压力
function generateUid(){ return call_user_func('str_shuffle', time());} //结果:4067524162
三、生成唯一uid的正确方法
虽然说上面的两种方式并非不可取
但是在大型公司必然不可取,一种是uid的格式必然纯数值,所以uuid方式可以排除
另外由于对数据库的压力起见,必然也不会采用第二种方式
而最经常采用的方式应该是使用数据库的主键索引,因为主键索引必然唯一
这里很多人会疑惑,主键索引不是会从1开始吗,这uid会有1位数的?
小了,格局小了,你可以设置主键索引的offset,让他从100000开始,不就可以解决这个问题了吗
这时候有人又问,那主键索引增加不是有规律的吗,比如插一条,会自增1
这时候就可以设置主键索引的增长步长,让他插入一条的步长不为1即可
而为了让uid看起来更加没有关联性,你可以设置步长为基数,比如3
这样增长起来,就会是100000,100003,100006,100009,100012....
补充
php中生成标准uuid的方法
UUID是指在一台机器上生成的数字,它保证对在同一时空中的所有机器都是唯一的。
通常平台 会提供生成UUID的API。UUID按照开放软件基金会(OSF)制定的标准计算,用到了以太网卡地址、纳秒级时间、芯片ID码和许多可能的数字。
由以 下几部分的组合:当前日期和时间(UUID的第一个部分与时间有关,如果你在生成一个UUID之后,过几秒又生成一个UUID,则第一个部分不同,其余相 同),时钟序列,全局唯一的IEEE机器识别号(如果有网卡,从网卡获得,没有网卡以其他方式获得),UUID的唯一缺陷在于生成的结果串会比较长。
关于 UUID这个标准使用最普遍的是微软的GUID(Globals Unique Identifiers)。
在ColdFusion中可以用CreateUUID()函数很简单的生成UUID,其格式为:xxxxxxxx-xxxx-xxxx- xxxxxxxxxxxxxxxx(8-4-4-16),其中每个 x 是 0-9 或 a-f 范围内的一个十六进制的数字。
而标准的UUID格式为:xxxxxxxx-xxxx-xxxx-xxxxxx-xxxxxxxxxx (8-4-4-4-12)
function guid(){ if (function_exists('com_create_guid')){ return com_create_guid(); }else{ mt_srand((double)microtime()*10000);//optional for php 4.2.0 and up. $charid = strtoupper(md5(uniqid(rand(), true))); $hyphen = chr(45);// "-" $uuid = chr(123)// "{" .substr($charid, 0, 8).$hyphen .substr($charid, 8, 4).$hyphen .substr($charid,12, 4).$hyphen .substr($charid,16, 4).$hyphen .substr($charid,20,12) .chr(125);// "}" return $uuid; }}echo guid();?>
到此这篇关于php生成唯一uid的解决方法详解的文章就介绍到这了。
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