An overview of Redis
Redis is said to be an open-source, in-memory data structure storage system, that is used as a database, a cache, and a message broker. Redis supports a variety of data structures like hashes, strings, lists, sets, bitmaps, hyperloglogs, sorted sets with range queries, geo-spatial indexes with radius queries as well as streams. It has LRU eviction, Lua scripting, built-in replication, transactions as well as different stages of on-disk persistence. This offers high availability through the Redis Sentinel and the automatic partitioning with the help of the Redis Cluster.
An individual who knows how to use Redis can run a number of operations, such as incrementing the value in a hash; appending to a string; computing set intersection; union and difference; pushing an element to a list, or collecting the member with the greatest ranking in a sorted set.
To achieve the outstanding performance, Redis operates with a built in-memory dataset.
Based on the use case, one can persist the same either by dumping a dataset to the disk once in a while or by attaching each of the commands to a log. Persistence can be easily disabled if one needs a networked, feature-rich, in-memory cache.
Redis even supports the trivial-to-setup master-slave asynchronous replication, alongside a very fast non-blocking synchronization, auto-reconnection with a partial resynchronization on the netsplit.
Features of Redis
Redis has been written in the ANSI C language and it works in most of the POSIX systems such as BSD, Linux, OS X without having any external dependencies. OS X and Linux are considered being the two operating systems where Redis has been developed and tested the most whereas Linux has been used for deploying the same. Redis might operate in the Solaris-derived systems such as SmartOS, but the support is the best effort. Unfortunately, there is no official support that is provided for the Windows builds, but Microsoft has developed and maintained a Win-64 port for Redis. In 2019, Redis celebrated its 10th anniversary. The other significant features of Redis are as follows:
1. High-Level of Data Structures – Redis offers five possible data options for the values. These are hashes, lists, sets, strings, and sorted sets. The operations which are unique to these data types are given and come along with the well-documented time-complexity (The Big O notation).
2. Efficient Performance – Because of its in-memory nature, a project manager’s commitment to ensuring that complexity stays at the bare minimum, as well as an event-based programming model, the application boasts of having an exceptional performance for the read and write operations.
3. Extremely Lightweight and No Dependencies –Redis is written in the ANSI C language, and it has limited to no external dependencies. The program works perfectly well in all the POSIX environments. The Windows platform is not officially supported for Redis, but an experimental build has been provided by Microsoft for the same.
4. High Availability – Redis has Built-in support for non-blocking, asynchronous, master/slave replication, in order to ensure high-level data availability. Presently there is a high-availability solution named as the Redis Sentinel which is currently usable, but it is still considered to be a work in progress project.
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Why use Redis?
So now coming to the usage of Redis, one might ask why to use Redis or what does one get by using Redis as compared to its other counterparts? Well, there is no doubt that Redis is a class apart from its other competitors. But what makes it unique is its creation and working efficiency. Below mentioned are some of the most important reasons why one should try Redis at least once.
1. Super-fast speed – Redis is blazingly fast! This is due to the fact that it has been written in the C language.
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2. NoSQL Database – Redis is a NoSQL Database.
3. Popular usage – Presently Redis is being used by a number of tech giants such as Pinterest, Snapchat, GitHub, Weibo, Digg, StackOverflow, Craigslist and Flickr to name a few.
4. Useful for Caching – In order to protect the cloud database calls and thus save some dollars out there, one can opt for caching through the Redis.
The popular usage of Redis
Redis’s simplicity, exceptionally speedy performance, as well as atomic manipulation of the data structures, offers itself for solving problems that are difficult or perform weakly when implemented along with the traditional relational databases. Some popular applications of Redis due to its versatile nature are as follows:
1. Queues – The projects such as Rescue makes use of Redis for the backend for queueing background jobs.
2. Publish and Subscribe – From the time of launch of version 2.0, Redis offers the capability to distribute the data by utilizing the Publish/Subscribe paradigm. Some of the organizations have shifted to Redis and gone away from the other message queuing systems (such as RabbitMQ, zerm, etc.) only because of Redis’s reliable performance and its simplicity.
3. Caching – Because of its high performance, a number of developers have turned to Redis at the time when the read and write operations volume exceeds the capabilities of the traditional databases. With its ability to persist the data to disk, Redis is considered to be a superior alternative as compared to the traditional solution for caching.
4. Counters – The atomic commands such as HINCRBY, gives access for simple and thread-safe implementation of the various counters. Forming a counter is as easy as determining the name for a key and then issuing a HINCRBY command. It is of no use to even read the data before incrementing it, and there are even no database schemes to be updated. As these are atomic operations that take place, the counters will assist in maintaining consistency when they are accessed from multiple application servers.
Famous organizations using REDIS
Redis has garnered and catered to the needs of its multiple users. Some important qualities that set apart Redis from the other key-value databases are that Redis has the ability to store as well as manipulate the high-level data types. Such data types are the fundamental data structures such as maps, sets, lists, as well as assorted sets. These are some of the data types which most of the developers are familiar with. Due to such ease of usage, Redis has found its place in the operating systems of popular organizations. Below mentioned are the details of how Redis is used in a particular organization.
1. GitHub –GitHub is said to be a web-based hosting service for the purpose of software development projects which use the Git revision control system. It offers paid plans for private repositories, as well as free accounts for the open-source projects. GitHub is presently considered to be the most famous code repository site for open source projects. GitHub was an early adopter of the Redis project. It has developed and open-sourced a library called Rescue, in order to facilitate the execution of the background jobs which have been placed in a queue. The GitHub developers took advantage of the fact that Redis was able to solve many of their difficult queueing issues. Thus the developers could remain focused on the difficult worker scheduling tasks.
2. Pinterest – Pinterest is a popular image website that has images based on different themes. Users are allowed to view, share as well as download high-quality images. Pinterest stores the user follower graphs within a Redis cluster where the data is shared with hundreds of different instances. Pinterest had started to use Redis after it found that their earlier solution of MySQL and Memcached had been reaching its limits.
3. Twitter – Twitter is a popular social networking site that allows users to share their views and opinions. Twitter has deployed a huge Redis cluster in order to store the timelines of all the users of the website. By utilizing the list of the data structure, Twitter is able to store the 800 most recent incoming tweets of a given user.
Limitations of Redis
Apart from the great list of advantages and benefits which Redis has to offer, like every resource, Redis too has a few drawbacks. Let’s have a look at some of the major challenges that one might face while using Redis.
1. Basic level of security: Redis only provides basic security (such as access rights) at the instance level. The RDBMS provides detailed, per-object access control lists (also known as role management).
2. Redis, a data structure server: In Redis, there is no query language, there are only commands. Nor is there any support for the relational algebra. One cannot submit any ad-hoc queries. All of the data accesses must be anticipated by a developer, and the proper data access paths should be designed. Due to this a lot of flexibility is believed to be lost.
3. Redis, an in-memory store: All of the data must fit into the memory. The RDBMS generally stores the information on disks and the cache part of the data in the memory. By using an RDBMS, one can manage more data than the memory which one has. This is not possible with Redis.
4. Redis has only 2 options for persistence: The regular snapshotting and the append-only files. None of these are as secure as the real transactional server offering redo/undo logging, point-in-time recovery, block checksumming, flashback capabilities, etc.
5. Needs Client Support – The clients are required to make the changes in order to support the Redis Clusters. The Redis Clusters have been around for a long time now, but there are still certain clients which do not support it.
6. Supports Only a single Database – Unlike the standalone databases, the Redis Clusters support only a single database (database 0). The SELECT command is not allowed in Redis.
7. The instance is not scalable – A unique Redis instance is not said to be scalable. It only operates on one CPU core in the single-threaded mode. In order to get scalability, a number of Redis instances need to be deployed and started. The distribution and sharing are done on the client-side (a developer needs to take care of these aspects). If one compares them to a unique Redis instance, most of the RDBMS offer more scalability. It provides parallelism at the connection level. They are said to be multi-processed (such as Oracle, PostgreSQL.) or even multi-threaded (such as MySQL, Microsoft SQL Server,), deriving benefits of the multi-core machines.
The culmination of high performance, high-level data structures, along with overall intuitiveness allows Redis to fill up the role like the Swiss Army knife of the data stores for any developer. Redis has been well suited for the purpose of solving challenges that are encountered at the time of developing real-time systems, due to the predictability of the operations that are applied to the data stored in the database of the system.
Redis attributes most of its performance to the fact that most of the data is always residing in the memory. The data can be persisted to a disk, but the incorrect configuration may lead to data loss when the system is shut down improperly. Thus with a few precautions, Redis is definitely a thumbs-up for developers.