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# Redis in 21 Minutes

Redis Home (opens new window)

Redis is an open source (BSD licensed), in-memory data structure store, used as a database, cache, and message broker.

# Online Playground

Try Redis (opens new window)

# Installation Optional

Ref (opens new window)

# Use Cases

Redis features will be detailed using "Blog Web app like Medium" in their simplified form.


  1. Manage user session
    • User profile:
      • name
      • followers
      • following
      • status
  2. Blog post statistics
    • Views, reads and claps statistics
    • Number of people who clapped
  3. Notifications
    • New
    • Recent notifications
  4. Latest Blogs
    • From the followings
  5. Blog search by title and tags

# Implementation

Redis key pattern should be decided for any use case.

# Manage User Session


  • Key - session:{user-id}:profile
  • Value - Hash data type

> hmset session:prasad_j:profile name Prasad followers 90 following 6 status online
OK
> hmget session:prasad_j:profile name status
1) "Prasad"
2) "online"
> hset session:prasad_j:profile status offline
(integer) 0
> hget session:prasad_j:profile status
"offline"
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# Blog Post Statistics

# Views, reads and claps statistics


  • Key - blog:{id}:stats
  • Value - Hash data type

> hmset blog:1001:stats views 0 reads 0 claps 0
OK
> hincrby blog:1001:stats claps 5
(integer) 5
> hmget blog:1001:stats views reads claps
1) "0"
2) "0"
3) "5"
> hgetall blog:1001:stats
1) "views"
2) "0"
3) "reads"
4) "0"
5) "claps"
6) "5"
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# Number of people who clapped for a blog


  • Key - blog:{id}:claps
  • Value - Set data type

  1. Add fan user-ids into a set
> sadd blog:1001:fans john
(integer) 1
> sadd blog:1001:fans harry mary
(integer) 1
> smembers blog:1001:fans
1) "mary"
2) "harry"
3) "john"
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  1. Add an existing fan into a set
> sadd blog:1001:fans harry
(integer) 0
> sismember blog:1001:fans harry
(integer) 1
> sadd blog:1002:fans harry
(integer) 1
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  1. Get the total members in a set
> scard blog:1001:fans
(integer) 3
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# Data Types

Redis is a key-value pair database. Key is a kind of string datatype. Value can be one of the following datatype

  • String
  • Hashes
  • Lists
  • Sets
  • Sorted Sets

An introduction to Redis data types and abstractions (opens new window)

# String

String is Simple Dynamic String (SDS) (opens new window). String can be used as number, array, bit set and binary data

struct sdshdr {
  long len;    // The free field stores the number of additional bytes available for use
  long free;   // The len field stores the length of buf
  char buf[];  // The buf character array stores the actual string
};
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TIP

  • The len field makes obtaining the length of a Redis string an O(1) operation.
  • Together the len and free field can be thought of as holding the metadata of the buf character array.

# Basic Commands

Full List of Commands (opens new window)

Command Args Purpose Time Complexity
SET (opens new window) key value [EX seconds] Set the string value of a key O(1)
SETNX (opens new window) key value Set the value of a key, only if the key does not exist O(1)
GET (opens new window) key Get the value of a key O(1)

For numerics only

Command Args Purpose Time Complexity
INCR (opens new window) key Increment the integer value of a key by one O(1)
INCRBY (opens new window) key increment Increment the integer value of a key by the given amount O(1)
INCRBYFLOAT (opens new window) key increment Increment the float value of a key by the given amount O(1)

Bitmaps are not an actual data type, but a set of bit-oriented operations defined on the String type.

Command Args Purpose Time Complexity
SETBIT (opens new window) key offset value Sets or clears the bit at offset in the string value stored at key O(1)
GETBIT (opens new window) key offset Get the bit value at offset in the string value stored at key O(1)
BITCOUNT (opens new window) key [start end] Count set bits in a string O(N)
BITOP (opens new window) operation destkey key [key ...] Perform a bitwise operation between multiple keys and store the result in the destination key O(N)

# Hash Map

Hashes, which are maps composed of fields associated with values. Both the field and the value are strings.

# Basic Commands

Full List of Commands (opens new window)

Command Args Purpose Time Complexity
HSET (opens new window) key field value [field value ...] Set the string value of a hash field O(1) / O(N)
HGET (opens new window) key field Get the value of a hash field O(1)
HGETALL (opens new window) key field Get all the fields and values in a hash O(N)
HMGET (opens new window) key field [field ...] Get the values of all the given hash fields O(1) / O(N)

# Sandbox Commands

Commands to keep your sandbox environment clean.

WARNING

Don't run these commands on any development or production server without proper understanding

$ redis-cli
> keys *
1) "entity:id"
> flushdb
OK
> keys *
(empty array)
>
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# References

Last Updated: 5/11/2021, 11:05:19 PM