键基础
Redis 键基础操作
Key | 键基础
-
使用非常长的
key 并不是好的主意，例如使用一个1024 字节(bytes) 长度的key 就很烂，其不仅仅耗费内存，而且在数据集中查找这个key 时也需要很高的比较成本。即使当前处理的任务是匹配存在的大值，采用哈希来处理( 例如使用SHA1) 会是一个更好的主意，特别是从内存和带宽的角度来看。 -
使用很短的
key 通常也不是一个好主意。将”u1000flw”作为一个key 几乎是毫无意义的，如果你可以将其替换成”user:1000:followers”，则它会更具可读性，而由此增加的空间与key 对象和值对象使用的空间比起来微乎其微。当简短的key 将明显的消耗一小部分内存，你的工作就是寻找到一个正确的平衡点。 -
尝试去坚持一个模式。例如使用”object-type:id”做为
key 就是一个好的想法，像”user:1000″。点或者虚线经常被用作多单词字段的连接符，例如”comment:1234-reply.to”或”comment-1234:reply-to”。 -
key 最大可分配512MB 。
Key 查询
遍历
有一些命令并未定义特定类型，但是在与EXISTS 命令返回DEL 命令将删除一个
> set mykey hello
OK
> exists mykey
(integer) 1
> del mykey
(integer) 1
> exists mykey
(integer) 0
> keys *
//查询所有的key值
从这个例子中可以看到，DEL 命令返回TYPE 命令结合使用的基本部分，TYPE 将返回指定
> set mykey x
OK
> type mykey
string
> del mykey
(integer) 1
> type mykey
none
Iteration
Keys are returned in incremental iterations with constant time guarantee for each iteration. A cursor (an integer is this case) is returned when the iterations is initialized and an updated cursor is returned and every iteration. An iteration cycle begins when the cursor is set to 0 in the SCAN request, and terminates when the cursor returned by the server is 0. Due to nuances of Redis architecture and the cursor algorithm implementation here are some peculiarities of this approach:
- A full iteration always retrieves all the elements that were present in the collection from the start to the end of a full iteration.
- A full iteration never returns any element that was NOT present in the collection from the start to the end of a full iteration.
- A given element may be returned multiple times. It is up to the application to handle the case of duplicated elements
- Elements that were not constantly present in the collection during a full iteration, may be returned or not: it is undefined.
- A number of elements returned during each count varies and can be 0 too. However, the iteration is not complete until the server returns the cursor value of 0.
- The COUNT option can be used to limit the number of elements returned in each iteration. The default value is 10. However, it is considered only a suggestion and not enforced in all cases. COUNT value can be changed during each iteration call.
- The MATCH option allows specifying of patterns like the KEYS command allows.
- The cursor implementation is completely stateless on the server side. That allows (potentially) infinite iterations to start in parallel. Also, there are no requirements of ensuring that an iteration continues up to the end and can be stopped anytime.
Key 操作
删除Key
DEL key Time complexity: O(N) where N is the number of keys that will be removed. When a key to remove holds a value other than a string, the individual complexity for this key is O(M) where M is the number of elements in the list, set, sorted set or hash. Removing a single key that holds a string value is O(1).
Key Expire
Key 的存活时间
在继续介绍复杂的数据结构之前，我们需要讨论另外一个与值类型无关的特性，它叫做DEL 命令是完全一样的。
几个关于
- 它们可以被设置为秒或者毫秒。
- 过期时间的精确度始终为
1 毫秒。 - 过期的信息会复制和保存在硬盘上，当你的
Redis 服务停止后，时间也是在走的( 意思是Redis 保存的是key 的过期日期) 。
过期的设置很简单：
> set key some-value
OK
> expire key 5
(integer) 1
> get key (immediately)
"some-value"
> get key (after some time)
(nil)
这个GET调用中间消失了，由于第二个调用延迟了EXPIRE 来进行过期设置PERSIST 可以用来移除一个过期而使这个SET 的选项：
> set key 100 ex 10
OK
> ttl key
(integer) 9
以上的例子，是将一个
不过，要注意一点，随着