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Redis

Redis (Remote Dictionary Service)​

Redis is an open source (BSD licensed), extremely fast, in-memory data structure store, used as a database, cache and message broker. It can optionally persist to a disk also. It supports different data structures like simple key-value pairs, sets, queues, strings, hashes, lists, sorted sets with range queries, bitmaps, hyprloglogs and geospatial indexes with radis queries. Redis has built-in replication, Lua scripting, LRU eviction, transactions and different levels of on-disk persistence, and provides high availability via Redis Sentinel and automatic partitioning with Redis Cluster

You can run atomic operations on these types, like appending to a string;incrementing the value in a hash;pushing an element to a list;computing set intersection, union and difference; or getting the member with highest ranking in a sorted set.

In order to achieve its outstanding performance, Redis works with anin-memory dataset. Depending on your use case, you can persist it either by dumping the dataset to disk every once in a while, or by appending each command to a log. Persistence can be optionally disabled, if you just need a feature-rich, networked, in-memory cache.

Redis also supports trivial-to-setup master-slave asynchronous replication, with very fast non-blocking first synchronization, auto-reconnection with partial resynchronization on net split.

Features​

  • Distributed Cache
  • Holds all data in-memory
  • Can also flush data into hard-drive
  • Master-slave, slaves can hold same data as master
  • Redis can also do key-value storage

Other features include​

Redis is written in ANSI C and works in most POSIX systems like Linux, *BSD, OS X without external dependencies.

Advantages​

  • Exceptionally fast− Redis is very fast and can perform about 110000 SETs per second, about 81000 GETs per second.
  • Supports rich data types− Redis natively supports most of the datatypes that developers already know such as list, set, sorted set, and hashes. This makes it easy to solve a variety of problems as we know which problem can be handled better by which data type.
  • Operations are atomic− All Redis operations are atomic, which ensures that if two clients concurrently access, Redis server will receive the updated value.
  • Multi-utility tool− Redis is a multi-utility tool and can be used in a number of use cases such as caching, messaging-queues (Redis natively supports Publish/Subscribe), any short-lived data in your application, such as web application sessions, web page hit counts, etc.

Optional Durability​

  • Journaling (append only log AOL)
  • Snapshotting
  • Both happens asynchronously in the background

Transport Protocol​

  • TCP
  • Request / response just like HTTP
  • Message format is RESP (REdis Serialization Protocol)

Redis 6​

Redis 6.0 open source

  • Access control lists (ACLs)
  • Improved evictions
  • Threaded I/O
  • RESP3 protocol

Redis Enterprise 6.0

  • Role-based access control (RBAC)
  • Extending active-active
  • HyperLogLog
  • Streams

Memory Footprint​

  • An empty instance uses ~ 3MB of memory
  • 1 Million small Keys -> String Value pairs use ~ 85MB of memory
  • 1 Million Keys -> Hash value, representing an object with 5 fields, use ~ 160 MB of memory

https://redis.io/topics/faq

Use Cases​

  • String
    • Session
    • Cache
    • Distributed Lock
  • Int
    • Counter
    • Rate Limiter
    • Global ID
  • Hash - Shopping Cart
  • Bitmap - User Retention
  • List - Message Queue
  • ZSet - Rank / Leaderboard

References​