In-Memory Database - Redis, Memcached

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Keeps data in the memory!

Basic Features

• implementing a high performance in-memory cache to decrease data access latency, increase throughput, and ease the load off your back-end systems.
• to store and manage session data for internet-scale applications in cases where persistence is not critical.

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Redis - Remote Dictionary Server

An in-memory key-value data store for use as a database, cache, message broker, and queue.

All Redis data resides in-memory, in contrast to databases that store data on disk or SSDs. By eliminating the need to access disks, in-memory data stores such as Redis avoid seek time delays and can access data in microseconds. Redis features versatile data structures, high availability, geospatial, Lua scripting, transactions, on-disk persistence, and cluster support making it simpler to build real-time internet scale apps. It works with relational or key-value databases to improve performance, such as MySQL, Postgres, Aurora, Oracle, SQL Server, DynamoDB, and more.

Unlike simplistic key-value data stores that offer limited data structures, Redis has a vast variety of data structures:

• Strings – text or binary data up to 512MB in size
• Lists – a collection of Strings in the order they were added
• Sets – an unordered collection of strings with the ability to intersect, union, and diff other Set types
• Sorted Sets – Sets ordered by a value
• Hashes – a data structure for storing a list of fields and values
• Bitmaps – a data type that offers bit level operations
• HyperLogLogs – a probabilistic data structure to estimate the unique items in a data set

Use Cases: Caching, Chat, messaging, and queues, Gaming leaderboards, Session store, Rich media streaming, Geospatial, Machine Learning, Real-time analytics

Language: Python, Java, PHP, C/C#/C++, Perl, Go, Ruby, JavaScript, Node.js

Comparison to other databases

Name	Type	Data storage options	Query types	Additional features
Redis	In-memory non-relational database	Strings, lists, sets, hashes, sorted sets	Commands for each data type for common access patterns, with bulk operations, and partial transaction support	Publish/Subscribe, master/slave replication, disk persistence, scripting (stored procedures)
memcached	In-memory key-value cache	Mapping of keys to values	Commands for create, read, update, delete, and a few others	Multithreaded server for additional performance
MySQL	Relational database	Databases of tables of rows, views over tables, spatial and third-party extensions	SELECT, INSERT, UPDATE, DELETE, functions, stored procedures	ACID compliant (with InnoDB), master/slave and master/master replication
PostgreSQL	Relational database	Databases of tables of rows, views over tables, spatial and third-party extensions, customizable types	SELECT, INSERT, UPDATE, DELETE, built-in functions, custom stored procedures	ACID compliant, master/slave replication, multi-master replication (third party)
MongoDB	On-disk non-relational document store	Databases of tables of schema-less BSON documents	Commands for create, read, update, delete, conditional queries, and more	Supports map-reduce operations, master/slave replication, sharding, spatial indexes

Resource

• https://redis.io
• https://en.wikipedia.org/wiki/Redis
• https://aws.amazon.com/redis
• https://github.com/Redsmin/redis-cheat-sheet
• Management tool https://github.com/joeferner/redis-commander
• https://redislabs.com/ebook/part-1-getting-started/chapter-1-getting-to-know-redis/1-1-what-is-redis/1-1-1-redis-compared-to-other-databases-and-software

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Memcached

Memcached has simpler use cases as it has fewer features. Primarily used for cache and session storage.

Language/Protocol Support: Python, Java, PHP, C/C#/C++, Perl, Go, Ruby, JavaScript, Node.js, ASCII protocol, Binary protocol, TCP & UDP protocols

Resource

• https://www.memcached.org
• https://github.com/memcached/memcached
• https://en.wikipedia.org/wiki/Memcached

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Difference

Feature	Memcached	Redis
Sub-millisecond latency	Yes	Yes
Developer ease of use	Yes	Yes
Data partitioning	Yes	Yes
Support for a broad set of programming languages	Yes	Yes
Advanced data structures	-	Yes
Multithreaded architecture	Yes	-
Snapshots	-	Yes
Replication	-	Yes
Transactions	-	Yes
Pub/Sub	-	Yes
Lua scripting	-	Yes
Geospatial support	-	Yes

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• Sub-millisecond latency Both Redis and Memcached support sub-millisecond response times. By storing data in-memory they can read data more quickly than disk based databases.

• Developer ease of use Both Redis and Memcached are syntactically easy to use and require a minimal amount of code to integrate into your application.

• Data partitioning Both Redis and Memcached allow you to distribute your data among multiple nodes. This allows you to scale out to better handle more data when demand grows.

• Support for a broad set of programming languages Both Redis and Memcached have many open-source clients available for developers. Supported languages include Java, Python, PHP, C, C++, C#, JavaScript, Node.js, Ruby, Go and many others.

• Advanced data structures In addition to strings, Redis supports lists, sets, sorted sets, hashes, bit arrays, and hyperloglogs. Applications can use these more advanced data structures to support a variety of use cases. For example, you can use Redis Sorted Sets to easily implement a game leaderboard that keeps a list of players sorted by their rank.

• Multithreaded architecture Since Memcached is multithreaded, it can make use of multiple processing cores. This means that you can handle more operations by scaling up compute capacity.

• Snapshots With Redis you can keep your data on disk with a point in time snapshot which can be used for archiving or recovery.

• Replication Redis lets you create multiple replicas of a Redis primary. This allows you to scale database reads and to have highly available clusters.

• Transactions Redis supports transactions which let you execute a group of commands as an isolated and atomic operation.

• Pub/Sub Redis supports Pub/Sub messaging with pattern matching which you can use for high performance chat rooms, real-time comment streams, social media feeds, and server intercommunication.

• Lua scripting Redis allows you to execute transactional Lua scripts. Scripts can help you boost performance and simplify your application.

• Geospatial support Redis has purpose-built commands for working with real-time geospatial data at scale. You can perform operations like finding the distance between two elements (for example people or places) and finding all elements within a given distance of a point.