Learning-relational database, non-relational database, distributed computing System __ Database

Acid principles for relational database compliance

(1) A Atomic nature:

All operations in a transaction, either done or done, the success of the transaction is the success of all operations in the transaction, as long as one operation fails, the entire transaction fails and needs to be rolled back.

(2) C Consistency:

The database should always be in a consistent state, and the operation of the transaction will not change the original consistency constraint in the database.

(3) I independence:

Concurrent transactions do not interact with each other, and if the data to be accessed by a transaction is being modified by another transaction, the data he accesses is not affected by the transaction as long as another transaction is not committed.

(4) D Durability:

Once the transaction is committed, his modifications will be permanently saved on the database, and will not be lost even if there is downtime.

Distributed Systems:

The distributed system consists of multiple computers and students ' software components that compute network connections (local or wide area networks) through home computing.

A distributed system is a software system that builds words and networks. Because of the nature of the software, distributed systems are highly cohesive and transparent.

Therefore, the difference between a network and a distributed system lies more in high-level software (especially the operating system) than in hardware.

Distributed systems can be applied to different platforms: PCs, workstations, LANs and WANs.

Advantages of distributed computing:

Reliability (Fault tolerance): one of the important advantages of distributed computing systems is reliability. The system crash of a single server does not affect the rest of the servers.

Scalability: More machines can be added to a distributed computing system as needed.

Resource sharing: Sharing resources is an essential application.

Flexibility: Easy to install

Faster speed: The ability to compute more than one computer allows him to process faster than other systems.

Open Systems: This service can be accessed either locally or remotely.

Higher performance: higher performance (ie, better price/performance) compared to a centralized cluster of computer networks.

Disadvantages of distributed computing

Trouble shooting

Software: The main drawbacks of less software support distributed computing systems

Network: Problems with network infrastructure

Security: The development of system features allows distributed computing systems to have the security of this data and the risk of sharing

What is NoSQL. (Not only SQL)

Non-relational database is a general designation of database management system which is different from traditional relational database.

NoSQL is used for large scale data storage, these types of data storage do not require a fixed pattern, without unnecessary operations can be extended horizontally.

Why to use NoSQL.

Data can be accessed and crawled easily through a third-party platform. User's personal information, social network, geographic location, user-generated data user action log has multiplied.

If the data is to be mined, the SQL database is no longer suitable for these applications, and the development of the NoSQL database can handle these large data well.

Cap theorem;

In computer science, the cap theorem, also known as the brewer theorem, points out that for a distributed computing system it is not possible to meet the following three points simultaneously:

• Consistency (all node words have the same data at the same time)

• Availability (ensure that every request word has a response regardless of success or failure)

• Segregation tolerance (loss or failure of any information in the system does not affect the continued operation of the system)

The core of CAP theory is that a distributed system can not meet the same consistency, availability and partition fault-tolerant three requirements, up to two.

Therefore, according to the CAP principle, the NoSQL database is divided into three categories: satisfying the CA principle, satisfying the CP principle and satisfying the AP principle.

· ca-a single point cluster, a system that satisfies consistency, usability, and is often less powerful in scalability.

· cp-satisfies consistency, partition tolerant systems, usually not particularly high performance.

· ap-systems that meet usability, partitioning tolerance, may often be less consistent.

What is MongoDB?

MongoDB is written by C + + language and is an open source database system based on distributed file storage.

In the case of high load, add more nodes, open source to ensure service-oriented performance.

MongoDB is designed to provide scalable, high-performance storage solutions for Web applications.

MongoDB stores data as a document with key-value pairs. The MongoDB document is similar to a JSON object.

Field values Open source contains other documents, an array-level document array.