redis的几个问题

没事读了一下hunangz的《redis设计与实现》
http://www.redisbook.com/en/latest/

写的很好，文档格式还特别好看，列几个有意思的点。

1，sds，Simple Dynamic String，要解决什么问题？
http://www.redisbook.com/en/latest/internal-datastruct/sds.html#redis

2，dictht/哈希表的结构
http://www.redisbook.com/en/latest/internal-datastruct/dict.html#id5
有个图，一看就懂～

3，rehash为什么要渐进进行？它的实现过程。
http://www.redisbook.com/en/latest/internal-datastruct/dict.html#id18
补充说明一下，python中的dict resize时就不是渐进的，set/insert item时有可能要调整。

4，rehash时的多线程竞争？
redis单线程。。。

5，温习skiplist
http://www.redisbook.com/en/latest/internal-datastruct/skiplist.html

6，ziplist的目的？以及实现
http://www.redisbook.com/en/latest/compress-datastruct/ziplist.html

7，redis的key为什么要加上类型？
http://www.redisbook.com/en/latest/datatype/object.html

8，亲切的小整数池
http://www.redisbook.com/en/latest/datatype/object.html#id3

9，redis的事务保证ACID了吗？
http://www.redisbook.com/en/latest/feature/transaction.html#acid
其中的I有可能影响并发能力。
温习一下ACID：
from http://en.wikipedia.org/wiki/ACID#Atomicity
-Atomicity requires that each transaction is “all or nothing”: if one part of the transaction fails, the entire transaction fails, and the database state is left unchanged.
原子性：全做/全不做
-The consistency property ensures that any transaction will bring the database from one valid state to another.
一致性：有效状态间迁移，不会跳到无效态（很久之前的有效态也算数）
-The isolation property ensures that the concurrent execution of transactions results in a system state that would be obtained if transactions were executed serially, i.e. one after the other.
隔离性：等效于某种顺序执行
-Durability means that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors.
持久性：一旦提交，全力保障永久有效。

10，lua脚本的安全性考虑
http://www.redisbook.com/en/latest/feature/scripting.html#id2