Key-value Key-Value storage principle first knowledge (NOSQL)

No-sql database: not just SQL

Definition: Non-relational database; NoSQL is used for storage of hyper-scale data. (for example, Google or Facebook collects trillions of bits of data for their users every day). These types of data stores do not require a fixed pattern and can be scaled horizontally without extra action. Further data mining and analysis is required.

RDBMS VS NOSQL

Rdbms	Nosql
Highly organized structured data	Represents more than just a SQL
Structured Query Language (SQL) (SQL)	No declarative query Language
Data and relationships are stored in separate tables	No pre-defined pattern
Data manipulation language, data definition language	Key-value pairs storage, column storage, document storage, graphics database
Strict consistency	Final consistency, not ACID properties
Basic transaction	Unstructured and unpredictable data
	Cap theorem
	High performance, highly available and scalable

The principle of weak requirements for usability and consistency: BASE

• Basically availble--Basic available
• Soft-state-Soft state/flexible transaction. "Soft state" can be understood as "no connection", while "hard state" is "connection oriented"
• Eventual consistency-final consistency is ultimately the ultimate goal of ACID.

NoSQL Database Classification

Type	Section represents	Characteristics
Column Storage	Hbase Cassandra Hypertable	As the name implies, data is stored in columns. The biggest feature is the convenient storage of structured and semi-structured data, easy to do data compression, for a column or a few columns of the query has a very large IO advantage.
Document storage	Mongodb Couchdb	Document storage is typically stored in a JSON-like format, and the stored content is document-based. This also gives you the opportunity to index certain fields and implement certain functions of the relational database.
Key-value Storage	Tokyo cabinet/tyrant Berkeley DB Memcachedb Redis	You can quickly query to its value with key. In general, the format of the store regardless of the value of the full receipt. (Redis includes other features)
Diagram Storage	Neo4j Flockdb	The best storage for graphical relationships. The use of traditional relational databases to address the performance of poor, and design use is not convenient.
Object storage	Db4o Versant	The database is manipulated by object-oriented syntax, and data is accessed through objects.
XML database	Berkeley DB XML BaseX	Efficiently stores XML data and supports internal query syntax for XML, such as Xquery,xpath.

Key-value Storage: (Redis-based)

The traditional relational database, dealing with a one-to-many problem, requires the foreign key to be placed on a multi-side, because there is no concept of aggregation in the RDBMS theory. With Redis, we can manage a one-to-many relationship at one end, using set.

If you use MySQL, when the data size is very large, the above two query operations need to rely on the table Association technology, and large table joins in large systems is a need to avoid the operation. Instead, each operation of Redis is confined to a smaller dataset, and the Key-value storage form, locating key is just a complex O (1) operation. With the very huge data volume, Redis performance is excellent, which is the advantage of NoSQL!

Key-value Key-Value storage principle first knowledge (NOSQL)