mysql 数据库设计_MySQL
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innodb表正好相反；行级锁表
互联网服务，不算支付性的服务外，互动产品，新闻系统等等一般都是读多，写少。用myisam表比较合适。
表的设计
定长表:所有列的字段长度都是定长的。可以去查mysql的手册不定长字段是VARCHAR、BLOB或TEXT。int char都是定长的，定长表占用空间会大。
动态表:就是字段不是都定长的。
定长表要比动态表检索速度快。
软件系统的设计习惯是把每张表都分清很明确的功能，比如用户表都是用户信息，如果需要同时从留言表取数据，又从用户表取用户信息的时候，就会采用联合查 询，有的时候一些操作还会用left,join等各种复杂sql语句，没准还要用mysql的函数。如果是针对访问量，读取量很大的互联网服务时，同时并 发去读，数据量又大，很可怕。最好是如果数据不会修改，在常用的表上有冗余字段，能够做到一次读，把数据都拿到；可以有冗余的写操作，但减少复杂的查询操 作。
在设计表的时候要将这个表的所有字段类型占用的字节数求和，并乘以你的预期（如:存储100W数据量），就是整张表未来会占用容量。
拆表 拆库
拆表就是将一张表复制N多张，里面分别存放不用内容的数据，数据的存放是用HASH算法来决定放入哪张表。
例如用户表user,传统情况就是一张表，拆表就是将表复制为user_01,user_02等里面都存放了格式一样的不同用户数据。
拆库和拆表类似，就是库的复制。
拆表或拆库有很多的HASH算法，主要目的就是减少表的数据量，用算法保证每个表的数据量平均，请求，读写操作被分摊降低压力，而且安全，出了问题最多是一部分用户受影响。缺点就是检索不方便，需要另想办法。
很多网站为了前期省事都会采用discuz的产品，如bbs,blog等，网上有不少关于这个产品的介绍和优化方法，没细研究过，听过一些网站介绍他们的 优化方法时，对于数据库主要是采用主从的方法，将数据库的读写分离来提高性能，但是个人觉得这种办法在数据量到了规模的时候就OVER了，并发和读写操作 没提升，数据也是会逐渐累计超过限制。
互联网服务由于要应对大数据量，大请求量，所以在设计开发的时候就不要太学院派，不要力图达到数据库、程序的设计“优美”，性能是最要紧的。bitsCN.com
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