Redis is an open-source, advanced key-value store and an apt solution for building high-performance, scalable web applications. Redis has three main peculiarities that set it apart:
- Redis holds its database entirely in the memory, using the disk only for persistence.
- Redis has a relatively rich set of data types compared to many key-value data stores.
- Redis can replicate data to any number of slaves.
1. KEY-VALUE OPERATIONS
1.1) SET:
Sets the value of the specified key.
Syntax:
SET key value
Example:
SET user:123 name “John Doe” email “john@example.com” age 30
Time Complexity: O(1)
1.2) GET:
Retrieves the value associated with the specified key.
Syntax:
GET key
Example:
GET user:123:name
Time Complexity: O(1)
1.4) DEL:
Deletes one or more keys and their associated values.
Syntax:
DEL key [key …]
Example:
DEL username
Time Complexity: O(N)
1.4) EXISTS:
Checks if the specified key exists in the database.
Syntax:
EXISTS key
Example:
EXISTS user:123
Time Complexity: O(1)
1.5) TTL:
Get the remaining time to live of a key in seconds.
Syntax:
TTL key
Example:
TTL mykey
Time Complexity: O(1)
1.6) EXPIRE :
Set a key’s time to live in seconds.
Syntax:
EXPIRE key seconds
Example:
EXPIRE mykey 60
Time Complexity: O(1)
1.7) INCR
Increments the number stored at a key by one.
Syntax
INCR key
Time complexity: O(1)
Increments the number stored at key by one. If the key does not exist, it is set to 0 before performing the operation. An error is returned if the key contains a value of the wrong type or contains a string that can not be represented as integer. This operation is limited to 64 bit signed integers.
1.8) DECR
Decrements the number stored at key by one. If the key does not exist, it is set to 0 before performing the operation. An error is returned if the key contains a value of the wrong type or contains a string that can not be represented as integer. This operation is limited to 64 bit signed integers.
Syntax
DECR key
Time complexity: O(1)
1.9) APPEND
The amortized time complexity is O(1) assuming the appended value is small and the already present value is of any size, since the dynamic string library used by Redis will double the free space available on every reallocation.
If key already exists and is a string, this command appends the value at the end of the string. If key does not exist it is created and set as an empty string, so APPEND will be similar to SET in this special case.
Syntax
APPEND key value
Time complexity: O(1).
2. LISTS:
2.1) LPUSH
adds a new element to the head of a list;
Syntax
LPUSH key element [element ...]
Time complexity:O(1) for each element added, so O(N) to add N elements when the command is called with multiple arguments.
2.2) RPUSH
adds to the tail.
Syntax
RPUSH key element [element ...]
Time complexity:
O(1) for each element added, so O(N) to add N elements when the command is called with multiple arguments.
2.3) LPOP
removes and returns an element from the head of a list.
Syntax
LPOP key [count]
Time complexity:
O(N) where N is the number of elements returned
2.4) RPOP
Does the same but from the tails of a list.
Syntax
RPOP key [count]
Time complexity:
O(N) where N is the number of elements returned
2.5) LLEN
returns the length of a list.
Syntax
LLEN key
Time complexity: O(1)
2.5) LRANGE
Returns the specified elements of the list stored at key. The offsets start and stop are zero-based indexes, with 0 being the first element of the list (the head of the list), 1 being the next element and so on.
Syntax
LRANGE key start stop
Time complexity:
O(S+N) where S is the distance of start offset from HEAD for small lists, from nearest end (HEAD or TAIL) for large lists; and N is the number of elements in the specified range.
3. SETS:
3.1) “sadd” command:
Creates a set, and adds element to it.
Syntax:
sadd set_name set_element
Example:
sadd SocialMedia Facebook Twitter WhatsApp.
Explanation:
We created a set namely “SocialMedia” and added 3 unique elements into it as “Facebook”, “Twitter”, “WhatsApp”.
3.2) “smembers” command:
Shows all the elements, present in that set.
Syntax:
smembers set_name
Example:
smembers SocialMedia
Explanation:
Previously, we stored “Facebook”, “Twitter”, “WhatsApp” in SocialMedia set. Hence, it’s displaying these elements.
3.3) “scard” command:
Shows no. of elements, present in that set.
Syntax:
scard set_name
Example:
scard SocialMedia
Explanation:
There ae 3 elements in this set, hence its showing 3 as output
3.4) “sismember” command:
Checks if that element exists in that set, if yes then returns 1
Syntax:
sismember set_name set_element
Example:
sismember SocialMedia Twitter
Explanation: Returned 1, “Twitter” is present in SocialMedia set.
3.5) “sdiff” command:
Shows difference of two sets by displaying those elements, elements that are in set 1 butt not in set 2.
Syntax:
sdiff set_name1 set_name2
Example:
sdiff FavSub1 FavSub2
Explanation:
FavSub1 and FavSub2 are two sets that contain favorite subjects of User1 and User2, respectively. Elements of FavSub1 and FavSub2 are {Computer Science, Data Science} and {Computer Science, Math’s}. The ouput of this command is showing diffrence of two sets as their elements that is the elements that are in FavSub1 but not in FavSub2. Hence, output is Data Science.
3.6) “sdiffstore” command:
Stores elements that differ in two sets, elements that are in set1 but not in set2 in a new set
Syntax:
sdiffstore set_name3 set_name1 set_name2
Example:
sdiffstore NewSet FavSub1 FavSub2
Explanation:
As the elements that differ in FavSub1 and FavSub2 is only Data Science. Hence, we made a new set namely “NewSet” that stored this element.
3.7) “sinter” command:
Shows elements that are present in both sets that is intersection of 2 given sets
Syntax:
sinter set_name1 set_name2
Example:
sinter FavSub1 FavSub2
Explanation:
Displaying Computer Science, as its the only common element present in both sets
3.8) “sinterstore” command:
Stores elements that are present in both sets in a new set.
Syntax:
sinterstore set_name4 set_name1 set_name2
Example:
sinterstore SamePinch FavSub1 FavSub2
Explanation:
SamePinch is a new set created that stores the elements that are common in FavSub1 and FavSub2 that is Computer Science
3.9) “sunion” command:
Shows all the unique elements that are there overall including those 2 sets as union of sets
Syntax:
sunion set_name1 set_name2
Example:
sunion FavSub1 FavSub2
Explanation: Displaying Computer Science, Maths and Data Science as these are the unique elements in whole as union of sets
3.10) “sunionstore” command:
Stores elements that are union of two sets in a new set
Syntax:
sunionstore set_name5 set_name1 set_name2
Example:
sunionstore Sub FavSub1 FavSub2
Explanation: Sub is a new set created that stores all the unique elements of whole in these 2 sets.
3.11) “srem” command:
Removes a particular element from given set.
Syntax:
srem set_name element
Example:
srem Sub Math’s
Explanation:
Removed Math’s element from the set “Sub”, hence output after executing srem commands is Data Science and Computer Science.
4. HASHES:
4.1) HSET (Hash Set):
Sets the value of a field in a Hash.
If the field does not exist, it creates the field and assigns the value.
Syntax:
HSET <key> <field> <value>
4.2) HGET (Hash Get):
Retrieves the value of a field in a Hash.
Syntax:
HGET <key> <field>
4.3) HDEL (Hash Delete):
Deletes one or more fields from a Hash.
Syntax:
HDEL <key> <field1> [<field2> … <fieldN>]
Example for HDEL:
Input:
HDEL user:123 age
HGET user:123 age
Output:
(nil)
4.4) HGETALL (Hash Get All):
Retrieves all fields and values of a Hash.
Syntax:
HGETALL <key>
Example for HGETALL:
Input:
HSET user:789 name “Charlie” country “USA”
HGETALL user:789
Output:
1) “name”
2) “Charlie”
3) “country”
4) “USA”
4.5) HKEYS (Hash Keys):
The HKEYS command retrieves all the field names in a hash.
Syntax:
HKEYS <key>
Example for HKEYS:
Input:
HSET user:2 username bob email bob@example.com age 25
HKEYS user:2
Output:
1) “username”
2) “email”
3) “age”
4.6) HVALS (Hash Values):
The HVALS command retrieves all the values in a hash.
Syntax:
HVALS <key>
Example for HVALS:
Input:
HSET preferences:456 theme “dark” language “en”
HVALS preferences:456
Output:
1) “dark”
2) “en”
5. PUB/SUB:
Channels are the communication pathways in Redis Pub/Sub. Messages are published to specific channels, and subscribers listen to messages on one or more channels. Channels are identified by names, e.g., “news,” “chatroom,” “events,” etc. When a message is published on a channel, all subscribers in that channel receive the message.
5.1) PUBLISH
Publishers use the PUBLISH command to send messages to channels. The
Syntax:
PUBLISH channel message
- channel: The name of the channel to which the message will be sent.
- message: The actual message content.
Example:
PUBLISH chat:general “Hello, everyone!”
Note:
In this example, the message “Hello, everyone!” is sent to the “chat:general” channel.
5.2) SUBSCRIBE
Subscribers use the SUBSCRIBE command to start listening to one or more channels. The
Syntax:
SUBSCRIBE channel [channel …]
channel: The name of the channel to subscriber is going to subscribe.
Example:
SUBSCRIBE chat:general
Note:
In this example, the subscriber starts listening to the “chat:general” channel.
5.3) UNSUBSCRIBE
Subscribers can unsubscribe from specific channels using the UNSUBSCRIBE command. The
Syntax:
UNSUBSCRIBE channel [channel …]
Example:
UNSUBSCRIBE chat:general
Note:
In this example, the subscriber stops listening to the “chat:general” channel.
6. OTHER COMMANDS:
6.1) SELECT
Select the Redis logical database having the specified zero-based numeric index. New connections always use the database 0.
Selectable Redis databases are a form of namespacing: all databases are still persisted in the same RDB / AOF file.
Syntax
SELECT index
Time complexity: O(1)
6.2) FLUSHDB
Delete all the keys of the currently selected DB. This command never fails.
By default, FLUSHDB will synchronously flush all keys from the database. Starting with Redis 6.2, setting the lazyfree-lazy-user-flush configuration directive to “yes” changes the default flush mode to asynchronous.
Syntax
FLUSHDB [ASYNC | SYNC]
Time complexity:
O(N) where N is the number of keys in the selected database
6.3) SAVE
The SAVE commands performs a synchronous save of the dataset producing a point in time snapshot of all the data inside the Redis instance, in the form of an RDB file.
Syntax
SAVE
Time complexity: O(N) where N is the total number of keys in all databases
6.4) BGSAVE
Save the DB in background.
Syntax
BGSAVE [SCHEDULE]
Time complexity: O(1)
Redis offers us various Sets commands, and above-mentioned ones are most important and prominent ones, there will be few commands that you may need to use as per your work requirements, in that case you can refer offical documentation of Redis. But for majority of your work with Sets in Redis, this article in itself is more than enough.
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