Data types and storage structures in Redis

Redis supports V data types: string (string), hash (hash), list, set (set), and Zset (sortedset: Ordered collection).

Redis defines a rich primitive command that can interact directly with a Redis server. In practice, we do not use these primitive commands directly, and Redis provides clients such as Java,c/c++,c#,php,javascript,perl,object-c,python,ruby,erlang, In most cases, we operate redis through a variety of clients. However, the client in any language is actually the encapsulation of the Redis primitive commands, and understanding the primitive commands helps to understand the design principles of the client and knows why.

3.1. String

The string is the most basic data type of redis, and the structure corresponds to one value for a key.

The string type is binary safe, meaning that it can contain any data, such as a JPG image or a serialized object.

The maximum capacity of a string type is 512M.

Unlike Linux, which has so many imaginative commands, it also likes to take a couple of inexplicable arguments. Redis's primitive command is simple, and there are rules to follow, in a nutshell, is clean crisp.

For example, we want to set up a user name to Redis and store it in String type:

127.0.0.1:6379> SET name Chenlongfei

Ok

"OK" is the response returned by Redis, representing the success of the setup.

Remove the value of this name:

127.0.0.1:6379> GET name

"Chenlongfei"

To change the value of name to "CLF", re-set again, overwriting the original value:

127.0.0.1:6379> SET name CLF

Ok

127.0.0.1:6379> GET name

"CLF"

To delete this piece of data:

127.0.0.1:6379> DEL name

(integer) 1--The total number of records that the number represents affects

127.0.0.1:6379> GET name

(nil)--nil representative is empty, the object does not exist

Adding and deleting the command a minute to learn, want to forget all difficult, mother no longer worry about my study.

command Format	Description
SET Key value	Sets the value of the specified key
GET Key	Gets the value of the specified key
setnx Key value	(set if Not Exist) Sets the value of key only if key does not exist
SETRANGE Key offset value	Use the value parameter to write to the string value stored by the key, starting with offset offsets
GETRANGE Key Start end	Returns the substring of a string value in key
getset Key value	Sets the value of the given key to value and returns the old value of key
MSET key value [key value ...]	(Multi set) simultaneously sets one or more key-value pairs
MGET key1 [Key2 ...]	Gets the value of all (one or more) given key
APPEND Key value	If key already exists and is a string, the APPEND command appends value to the end of the original value of the key
Setex Key seconds value	(set Expire) associates the value of values to the key and sets the expiration time of the key to seconds (in seconds)
Psetex Key milliseconds value	(Precise set Expire) This command is similar to the Setex command, but it sets the lifetime of the key in milliseconds, rather than as the Setex command, in seconds
STRLEN Key	Returns the length of the string value stored by key
INCR Key	Increment the numeric value stored in key by one, provided that value is a number
Incrby Key increment	Adds the value stored by key to the given increment value, provided that value is a number
incrbyfloat Key increment	Adds the value stored by key to the given floating-point increment value if value is a number
DECR Key	Subtract the numeric value stored in key by one, provided that value is a number
Decrby Key Decrement	The value stored by key minus the given decrement value, provided that value is a number

3.2. Hash

A Redis hash is a mapping between field and value, a collection of key-value pairs, so it is particularly well-suited for storing objects.

Each hash in Redis can store up to 232-1 key-value pairs (more than 4 billion).

For example, we want to store a user's information in Redis, including the user ID, username, and three fields of the email address:

127.0.0.1:6379>hmset user_1 userId 123 userName CLF Email chenlongfei@163.com

Ok

127.0.0.1:6379> Hgetall user_1

1) "UserId"

2) "123"

3) "UserName"

4) "CLF"

5) "Email"

6) "Chenlongfei@163.com"

command Format	Description
hmset key field1 value1 [Field2 value2 ...]	(Hash Multi Set) simultaneously sets multiple field-value pairs to the hash table key
hmget key field1 [Field2 ...]	Gets the value of all given fields
hset key field value	Sets the value of the field in the hash table key to
hget key field	Gets the value stored in the specified field in the hash table
Hgetall Key	Get all fields and values that specify key in the hash table
Hdel Key field2 [Field2]	Delete one or more hash table fields
hsetnx key field value	Set the value of the hash table field only if the field is not present
Hkeys Key	Gets the fields from all the hash tables
hvals Key	Get all values in the hash table
hexists key field	View Hash table key, whether the specified field exists
Hlen Key	Gets the number of fields in the hash table
hincrby key field increment	Adds an increment to the integer value of the specified field in the hash table key
hincrbyfloat key field increment	Adds an increment to the floating point value of the specified field in the hash table key

3.3. List

The Redis list is a simple list of strings, sorted by insertion order. Support for adding an element to the list header (left) or tail (right) operation.

A list can contain up to 232-1, or more than 4 billion elements.

For example, we would like to use a list named "Continents" to put the names of five continents:

127.0.0.1:6379> lpush Continents Asia Africa America Oceania Antarctica

(integer) 5

127.0.0.1:6379> Lrange Continents 0 4 --Get the element labeled 0~4

1) "Antarctica"

2) "Oceania"

3) "America"

4) "Africa"

5) "Asia"

Although the Redis list is named as a list, in fact it is more like a stack in terms of features, with the most recently placed elements as the head, with the oldest element in the tail, so the subscript of the Redis list is in reverse order. In the above example, the five elements are put in sequence: Asia, Africa, America, Oceania, Antarctica, subscript 4, 3, 2, 1, 0 respectively. This is completely different from the concept of list in Java and requires special attention.

Similar to the stack, when performing a pop operation, the Redis list pops up the newest element, similar to the top element of the stack.

The Redis list also supports a blocking operation such as BLPOP (the abbreviation forBlockd List Pop ), moving out and getting the first element of the list, If the list does not have an element (or the list does not exist) it blocks the list until it waits for a timeout or discovers that it can eject the element.

For example, we execute the blpop command on a nonexistent list "myList":

Blpopmylist 20--pops the first element of the MyList list, if not, blocks for 20 seconds

The client goes into a blocking state, and if the list is stored in the element within 20 seconds, it pops up:

27.0.0.1:6379> blpop myList ----if no element is blocked, the time limit is 20 seconds.

1) "MyList"

2) "Hello"

(6.20s)

If the element is still not waiting after the timeout, the end is blocked and nil is returned:

127.0.0.1:6379> Blpop myList

(nil)

(20.07s)

command Format	Description
lpush key value1 [value2 ...]	Insert one or more values into the list header
Lpop Key	Move out and get the first element of a list
lpushx Key value	(List Push If exist) inserts one or more values into the existing list header
LINDEX Key index	Get the elements in a list by index
Lrange key Start stop	Gets the element within the specified range of the list
LSET Key index value	To set the value of a list element by index
LTRIM key Start stop	Only elements within the specified interval are preserved, and elements that are not within the specified range are deleted
Rpop Key	(Rear Pop) Remove and get the last element of the list
rpush key value1 [value2 ...]	Insert one or more values into the tail of the list
rpushx Key value	Inserts one or more values at the end of a list that already exists
Lrem Key Count value	Removes the element with the value of the field from the list, removes count of the absolute value after the end, Count > 0 is removed from the table header, count < 0 is removed from the footer; count=0 all deleted
rpoplpush Source destination	Removes the last element of the list and adds the element to another list and returns
blpop key1 [key2 ...] timeout	Moves out and gets the first element of the list, if the list has no elements that block the list until the wait time-out or the popup element is found, and if timeout is 0, it waits forever.
brpop key1 [key2 ...] timeout	Moves out and gets the last element of the list, if the list has no elements that block the list until the wait time-out or the popup element is found, and if timeout is 0, it waits forever.
Linsert key before | after pivot value	Look for pivot in the key list and insert value before pivot value |
Llen Key	Get list length

3.4. Collection

A Redis collection is an unordered collection of type string. A collection member is unique , which means that duplicate data cannot appear in the collection.

Redis collections are implemented by hash tables, so the complexity of adding, deleting, and finding is O (1).