Redis - Technological watch

Introduction

Redis, which stands for Remote Dictionary Server, is a source-available, in-memory storage system. It was developed and maintained by Salvatore Sanfilippo, starting in 2009. Redis is used as a distributed, in-memory key-value database, cache, and message broker, with optional durability. Redis holds all data in memory and due to its design, it offers low-latency reads and writes, making it particularly suitable for use cases that require a cache. Redis is the most popular NoSQL database and is used in companies like Twitter, Airbnb, Tinder, Yahoo, Adobe, and Amazon.

Usage

The syntax of Redis is very simple:

# Setting the key mykey to the string value "Hello world"
SET mykey "Hello world"

# Retrieve the value associated with mykey
GET mykey

# Delete the key
DEL mykey

# Check if the key exists
EXISTS mykey

# Increment/decrement value
INCR days
DECR days

# Define temporary variables
SET sidebar "<div>Sidebar</div>" # set a key with TTL=-1 (no TTL)
TTL sidebar
EXPIRE sidebar 120

Data types

Redis supports different kinds of abstract data structures. Here are some of the core data types that Redis Community Edition implements (https://redis.io/docs/latest/develop/data-types/):

String

Redis strings are the most basic Redis data type, representing a sequence of bytes:

SET mykey "Hello World"
GET mykey

Hash

Redis hashes are record types modeled as collections of field-value pairs:

HMSET user:1000 username Alex birthyear 1999 verified 1
HGETALL user:1000

List

Redis lists are lists of strings sorted by insertion order:

RPUSH posts "Redis" # push on the right
LPUSH posts "Vault" # push on the left
LRANGE posts 0 -1 # show the elements of the list from x to y element
LLEN posts
LPOP posts # remove an element in the left
RPOP posts # remove an element in the right

Set

Redis sets are unordered collections of unique strings:

SADD users "Alex"
SADD users "Hugo"
SMEMBERS users

SREM users "Hugo"
SISMEMBER users "Alex" # check if an element exists

SUNION users users2 # merge 2 sets

Sorted Set

Redis sorted sets are collections of unique strings that maintain order by each string’s associated score:

ZADD myzset 1 "one"
ZADD myzset 2 "two"
ZRANGE myzset 0 -1 WITHSCORES

Stream

A Redis stream is a data structure that acts like an append-only log:

XADD mystream * sensor-id 1234 temperature 20.2
XRANGE mystream - +

Bitmap

Redis bitmaps let you perform bitwise operations on strings:

SETBIT mykey 7 1
GETBIT mykey 7

Bitfield

Redis bitfields efficiently encode multiple counters in a string value:

BITFIELD mykey INCRBY i5 100 1 GET u4 0

Geo-spatial

Redis geo-spatial indexes are useful for finding locations within a given geographic radius or bounding box:

GEOADD France 2.349014 48.864716 "Paris" 6.184417 48.692054 "Nancy"
GEODIST France Paris Nancy

Ecosystem

Redis has a rich ecosystem of modules that extend its capabilities beyond the core data structure server. Here are some of the key modules (https://redis.io/docs/latest/integrate/):

1. RedisSearch: RedisSearch is a full-text search engine that provides querying, secondary indexing, and full-text search for Redis. It allows you to index your data in a variety of ways, and then search and aggregate it very quickly.
2. RedisGraph: RedisGraph is a graph database module for Redis. It implements the Cypher query language, and uses a fast, memory-efficient graph algorithm library called GraphBLAS. RedisGraph represents connected data in a compact format that allows for efficient processing of complex graph queries.
3. RedisBloom: RedisBloom is a module that provides probabilistic data structures to Redis. It includes structures like Bloom filters and Count-Min sketches, which allow you to handle tasks like membership queries and frequency counting in a memory-efficient way.
4. RedisJSON: RedisJSON is a module that provides native JSON capabilities to Redis. It allows you to store, update, and fetch JSON values from Redis keys.
5. RedisAI: RedisAI is a module that turns Redis into an AI server. It provides a set of commands for running popular deep learning models, and it allows you to execute AI operations in real-time.
6. RedisTimeSeries: RedisTimeSeries is a module that provides time series data structures to Redis. It allows you to store, retrieve, and analyze time series data at high speeds.
7. RedisGears: RedisGears is a serverless engine for transaction, batch, and event-driven operations. It allows you to execute scripts that can process data across all of Redis’ data structures.

When NOT to Use Redis

• Big Data Storage: Redis stores data in RAM, making it less suitable for handling large datasets. For extensive data storage, it’s better to use Redis for caching purposes rather than as a primary database.
• ACID Transactions: Redis does not fully support ACID (Atomicity, Consistency, Isolation, Durability) transactions. For more details, you can read my blog post on the CAP theorem.

When to Use Redis

• Caching: Redis is excellent for caching, which can significantly speed up data access and improve application performance.
• Session Management: Use Redis to handle sessions efficiently, providing fast and reliable session storage.
• Queues: Redis is excellent for transferring data between servers using queues, facilitating smooth and reliable data handling in real-time applications.

Pricing

For additional details on pricing and licenses, please follow the provided links:

• https://redis.io/legal/licenses/
• https://redis.io/pricing/

Try with Docker

You can easily try Redis with docker:

docker run --name my-redis -d redis
docker exec -it my-redis redis-cli

SET hello "Hello, Redis!"
GET hello

docker stop my-redis
docker rm my-redis