Redis1: Introduction to Redis, basic features of Redis, relational database, non-relational database, database development stage

Introduction to Redis

Remote Dictionary Service: The translation is the Remote Dictionary Service, or redis for short.

Why use redis, you need to first understand the difference between relational databases and non-relational databases, that is, the difference and usage scenarios between SQL and NoSQL.

Acid (ACID) Base (BASE) Principles for Database Design

Relational Database

Commonly known as SQL database, mainstream MySQL, Oracle.

Characteristics of relational databases

1. Store data based on rows, two-dimensional mode (stored in a table, with rows and columns)
2. Storing structured data, the data is stored with a fixed schema
3. Relationship exists between tables
4. Most support SQL (Structured Query Language) operations and complex associated queries
5. Provide strict or real-time data consistency by supporting transactional ACID (acid)

Weaknesses of relational databases

1. It is difficult to achieve expansion, only upward (vertical) expansion is possible, dynamic expansion and contraction are not supported. If you want to achieve horizontal expansion, you need to introduce some complex technologies, such as sub-database and sub-table
2. The table structure is difficult to modify, so the format of the stored data is also limited
3. In the case of high concurrency, the disk-based read and write pressure is relatively large

Non-relational database

non relational, or NoSQL, mainstream Redis, MongoDB.
At the beginning, it was called NoSQL, because it did not support the operation of Structured Query Language (SQL), and later evolved into not only SQL, not just SQL.

Non-relational database features

1. Store unstructured data such as text, images, audio, video
2. There is no association between tables, and the scalability is strong
3. Ensure the eventual consistency of data and follow the BASE (base) theory
4. Support massive data storage and high concurrent efficient read and write
5. Support distributed, can store data in shards, easy to expand and shrink

Types of NoSQL

1. KV Storage: Redis and Memcached
2. Document Storage: MongoDB
3. Column Store: HBase
4. Graph storage: Neo4j
5. Object Storage
6. XML Storage
7. ······

Database development stage

Features	SQL	NoSQL	NewSQL (such as TiDB)
Relational Model	√	×	√
SQL syntax	√	×	√
ACID	√	×	√
Horizontal expansion	×	√	√
Mass data	×	√	√
Unstructured	×	√	√

Redis basic features

1. Fast speed, placed in memory
2. Supports multiple data types (Memcached only supports KV)
3. Multiple programming languages ​​supported
4. Persistence, memory elimination (Memcached has no persistence mechanism)
5. Function-rich: transaction, publish-subscribe, pipeline, lua
6. Cluster, distributed (Memcached does not support the master-slave setting of the cluster, Memcached is designed to be multi-threaded)