Redis 字符串
Redis 字符串简介
Redis 字符串存储字节序列，包括文本、序列化对象和二进制数组。 因此，字符串是您可以关联的最简单的值类型 一个 Redis 密钥。 它们通常用于缓存，但它们支持其他功能，这些功能允许您实现计数器并执行按位运算。
由于 Redis 键是字符串，因此当我们也使用字符串类型作为值时， 我们正在将一个字符串映射到另一个字符串。字符串数据类型很有用 适用于许多用例，例如缓存 HTML 片段或页面。
As you can see using the SET and the GET commands are the way we set
and retrieve a string value. Note that SET will replace any existing value
already stored into the key, in the case that the key already exists, even if
the key is associated with a non-string value. So SET performs an assignment.
Values can be strings (including binary data) of every kind, for instance you
can store a jpeg image inside a value. A value can't be bigger than 512 MB.
The SET command has interesting options, that are provided as additional
arguments. For example, I may ask SET to fail if the key already exists,
or the opposite, that it only succeed if the key already exists:
There are a number of other commands for operating on strings. For example
the GETSET command sets a key to a new value, returning the old value as the
result. You can use this command, for example, if you have a
system that increments a Redis key using INCR
every time your web site receives a new visitor. You may want to collect this
information once every hour, without losing a single increment.
You can GETSET the key, assigning it the new value of "0" and reading the
old value back.
The ability to set or retrieve the value of multiple keys in a single
command is also useful for reduced latency. For this reason there are
the MSET and MGET commands:
When MGET is used, Redis returns an array of values.
Strings as counters
Even if strings are the basic values of Redis, there are interesting operations
you can perform with them. For instance, one is atomic increment:
The INCR command parses the string value as an integer,
increments it by one, and finally sets the obtained value as the new value.
There are other similar commands like INCRBY,
DECR and DECRBY. Internally it's
always the same command, acting in a slightly different way.
What does it mean that INCR is atomic?
That even multiple clients issuing INCR against
the same key will never enter into a race condition. For instance, it will never
happen that client 1 reads "10", client 2 reads "10" at the same time, both
increment to 11, and set the new value to 11. The final value will always be
12 and the read-increment-set operation is performed while all the other
clients are not executing a command at the same time.
Limits
By default, a single Redis string can be a maximum of 512 MB.
Basic commands
Getting and setting Strings
SET stores a string value.SETNX stores a string value only if the key doesn't already exist. Useful for implementing locks.GET retrieves a string value.MGET retrieves multiple string values in a single operation.
Managing counters
INCR atomically increments counters stored at a given key by 1.INCRBY atomically increments (and decrements when passing a negative number) counters stored at a given key.- Another command exists for floating point counters:
INCRBYFLOAT.
Bitwise operations
To perform bitwise operations on a string, see the bitmaps data type docs.
See the complete list of string commands.
Performance
Most string operations are O(1), which means they're highly efficient.
However, be careful with the SUBSTR, GETRANGE, and SETRANGE commands, which can be O(n).
These random-access string commands may cause performance issues when dealing with large strings.
Alternatives
If you're storing structured data as a serialized string, you may also want to consider Redis hashes or JSON.
Learn more
- Redis Strings Explained is a short, comprehensive video explainer on Redis strings.
- Redis University's RU101 covers Redis strings in detail.
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